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[
"Economic themes"
]
| Robert Phiddian's article "Have you eaten yet? The Reader in A Modest Proposal" focuses on two aspects of ''A Modest Proposal'': the voice of Swift and the voice of the Proposer. Phiddian stresses that a reader of the pamphlet must learn to distinguish between the satirical voice of Jonathan Swift and the apparent economic projections of the Proposer. He reminds readers that "there is a gap between the narrator's meaning and the text's, and that a moral-political argument is being carried out by means of parody". While Swift's proposal is obviously not a serious economic proposal, George Wittkowsky, author of "Swift's Modest Proposal: The Biography of an Early Georgian Pamphlet", argues that to understand the piece fully it is important to understand the economics of Swift's time. Wittowsky argues that not enough critics have taken the time to focus directly on the mercantilism and theories of labour in 18th century England. "If one regards the ''Modest Proposal'' simply as a criticism of condition, about all one can say is that conditions were bad and that Swift's irony brilliantly underscored this fact". | 665 | A Modest Proposal | [
"Essays by Jonathan Swift",
"Satirical essays",
"Pamphlets",
"18th-century essays",
"Works published anonymously",
"British satire",
"1729 in Great Britain",
"Cannibalism in fiction",
"1729 books"
]
| []
|
[
"Economic themes",
"\"People are the riches of a nation\""
]
| At the start of a new industrial age in the 18th century, it was believed that "people are the riches of the nation", and there was a general faith in an economy that paid its workers low wages because high wages meant workers would work less. Furthermore, "in the mercantilist view no child was too young to go into industry". In those times, the "somewhat more humane attitudes of an earlier day had all but disappeared and the laborer had come to be regarded as a commodity". Louis A. Landa composed a conducive analysis when he noted that it would have been healthier for the Irish economy to more appropriately utilize their human assets by giving the people an opportunity to "become a source of wealth to the nation" or else they "must turn to begging and thievery". This opportunity may have included giving the farmers more coin to work for, diversifying their professions, or even consider enslaving their people to lower coin usage and build up financial stock in Ireland. Landa wrote that, "Swift is maintaining that the maxim—people are the riches of a nation—applies to Ireland only if Ireland is permitted slavery or cannibalism" Landa presents Swift's ''A Modest Proposal'' as a critique of the popular and unjustified maxim of mercantilism in the 18th century that "people are the riches of a nation". Swift presents the dire state of Ireland and shows that mere population itself, in Ireland's case, did not always mean greater wealth and economy. The uncontrolled maxim fails to take into account that a person who does not produce in an economic or political way makes a country poorer, not richer. Swift also recognises the implications of this fact in making mercantilist philosophy a paradox: the wealth of a country is based on the poverty of the majority of its citizens. Swift however, Landa argues, is not merely criticising economic maxims but also addressing the fact that England was denying Irish citizens their natural rights and dehumanising them by viewing them as a mere commodity. | 665 | A Modest Proposal | [
"Essays by Jonathan Swift",
"Satirical essays",
"Pamphlets",
"18th-century essays",
"Works published anonymously",
"British satire",
"1729 in Great Britain",
"Cannibalism in fiction",
"1729 books"
]
| []
|
[
"The public's reaction"
]
| Swift's essay created a backlash within the community after its publication. The work was aimed at the aristocracy, and they responded in turn. Several members of society wrote to Swift regarding the work. [[Allen Bathurst, 1st Earl Bathurst|Lord Bathurst]]'s letter intimated that he certainly understood the message, and interpreted it as a work of comedy: 12 February 1729–30:"I did immediately propose it to Lady Bathurst, as your advice, particularly for her last boy, which was born the plumpest, finest thing, that could be seen; but she fell in a passion, and bid me send you word, that she would not follow your direction, but that she would breed him up to be a parson, and he should live upon the fat of the land; or a lawyer, and then, instead of being eat himself, he should devour others. You know women in passion never mind what they say; but, as she is a very reasonable woman, I have almost brought her over now to your opinion; and having convinced her, that as matters stood, we could not possibly maintain all the nine, she does begin to think it reasonable the youngest should raise fortunes for the eldest: and upon that foot a man may perform family duty with more courage and zeal; for, if he should happen to get twins, the selling of one might provide for the other. Or if, by any accident, while his wife lies in with one child, he should get a second upon the body of another woman, he might dispose of the fattest of the two, and that would help to breed up the other.The more I think upon this scheme, the more reasonable it appears to me; and it ought by no means to be confined to Ireland; for, in all probability, we shall, in a very little time, be altogether as poor here as you are there. I believe, indeed, we shall carry it farther, and not confine our luxury only to the eating of children; for I happened to peep the other day into a large assembly [Parliament] not far from Westminster-hall, and I found them roasting a great fat fellow, [Walpole again] For my own part, I had not the least inclination to a slice of him; but, if I guessed right, four or five of the company had a devilish mind to be at him. Well, adieu, you begin now to wish I had ended, when I might have done it so conveniently". | 665 | A Modest Proposal | [
"Essays by Jonathan Swift",
"Satirical essays",
"Pamphlets",
"18th-century essays",
"Works published anonymously",
"British satire",
"1729 in Great Britain",
"Cannibalism in fiction",
"1729 books"
]
| []
|
[
"Modern usage"
]
| ''A Modest Proposal'' is included in many literature courses as an example of [[Satire#Early modern western satire|early modern western satire]]. It also serves as an introduction to the concept and use of argumentative language, lending itself to secondary and post-secondary essay courses. Outside of the realm of English studies, ''A Modest Proposal'' is included in many comparative and global literature and history courses, as well as those of numerous other disciplines in the arts, humanities, and even the social sciences. The essay's approach has been copied many times. In his book ''A Modest Proposal'' (1984), the evangelical author [[Francis Schaeffer]] emulated Swift's work in a social conservative polemic against abortion and [[euthanasia]], imagining a future [[dystopia]] that advocates [[recycling]] of aborted [[embryos]], [[fetuses]], and some disabled infants with compound intellectual, physical and physiological difficulties. (Such [[Baby Doe Rules]] cases were then a major concern of the US [[anti-abortion]] movement of the early 1980s, which viewed selective treatment of those infants as [[disability discrimination]].) In his book ''A Modest Proposal for America'' (2013), statistician [[Howard Friedman]] opens with a satirical reflection of the extreme drive to fiscal stability by ultra-conservatives. In the 1998 edition of ''[[The Handmaid's Tale]]'' by [[Margaret Atwood]] there is a quote from ''A Modest Proposal'' before the introduction. ''[[A Modest Video Game Proposal]]'' is the title of an open letter sent by activist/former attorney [[Jack Thompson (activist)|Jack Thompson]] on 10 October 2005. He proposed that someone should "create, manufacture, distribute, and sell a video game" that would allow players to act out a scenario in which the game character kills video game developers. [[Hunter S. Thompson]]'s ''[[Fear and Loathing in America|Fear and Loathing in America: The Brutal Odyssey of an Outlaw Journalist]]'' includes a letter in which he uses Swift's approach in connection with the [[Vietnam War]]. Thompson writes a letter to a local [[Aspen, Colorado|Aspen]] newspaper informing them that, on Christmas Eve, he is going to use [[napalm]] to burn a number of dogs and hopefully any humans they find. The letter protests against the burning of Vietnamese people occurring overseas. The 2013 horror film ''Butcher Boys,'' written by the original [[The Texas Chain Saw Massacre]] scribe [[Kim Henkel]], is said to be an updating of Jonathan Swift's ''A Modest Proposal.'' Henkel imagined the descendants of folks who actually took Swift up on his proposal. The film opens with a quote from J. Swift. On 30 November 2017, Jonathan Swift's 350th birthday, ''[[The Washington Post]]'' published a column entitled "Why Alabamians should consider eating Democrats' babies", by [[Alexandra Petri]]. In July 2019, [[E. Jean Carroll]] published a book titled ''[[What Do We Need Men For?: A Modest Proposal]]'', discussing problematic behaviour of male humans. On 3 October 2019, a satirist spoke up at an event for [[Alexandria Ocasio-Cortez]], claiming that a solution to the [[climate crisis]] was "we need to eat the babies". The individual also wore a T-shirt saying "Save The Planet, Eat The Children". This stunt was understood by many as a modern application of ''A Modest Proposal''. | 665 | A Modest Proposal | [
"Essays by Jonathan Swift",
"Satirical essays",
"Pamphlets",
"18th-century essays",
"Works published anonymously",
"British satire",
"1729 in Great Britain",
"Cannibalism in fiction",
"1729 books"
]
| []
|
[]
| The '''alkali metals''' consist of the [[chemical element]] [[lithium]] (Li), [[sodium]] (Na), [[potassium]] (K), [[rubidium]] (Rb), [[caesium]] (Cs), and [[francium]] (Fr). Together with [[hydrogen]] they constitute [[Group (periodic table)#Group names|group 1]], which lies in the [[s-block]] of the [[periodic table]]. All alkali metals have their outermost electron in an [[atomic orbital|s-orbital]]: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of [[periodic trends|group trends]] in properties in the periodic table, with elements exhibiting well-characterised [[homology (chemistry)|homologous]] behaviour. This family of elements is also known as the '''lithium family''' after its leading element. The alkali metals are all shiny, [[hardness|soft]], highly [[reactivity (chemistry)|reactive]] metals at [[standard temperature and pressure]] and readily lose their [[valence electron|outermost electron]] to form [[cations]] with [[electric charge|charge]] +1. They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to [[redox|oxidation]] by atmospheric moisture and [[oxygen]] (and in the case of lithium, [[nitrogen]]). Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in [[salt (chemistry)|salts]] and never as the free elements. Caesium, the fifth alkali metal, is the most reactive of all the metals. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones. All of the discovered alkali metals occur in nature as their compounds: in order of [[abundance of the chemical elements|abundance]], sodium is the most abundant, followed by potassium, lithium, rubidium, caesium, and finally francium, which is very rare due to its extremely high [[radioactivity]]; francium occurs only in minute [[trace radioisotope|traces]] in nature as an intermediate step in some obscure side branches of the natural [[decay chain]]. Experiments have been conducted to attempt the synthesis of [[ununennium]] (Uue), which is likely to be the next member of the group; none was successful. However, ununennium may not be an alkali metal due to [[relativistic quantum chemistry|relativistic effects]], which are predicted to have a large influence on the chemical properties of [[superheavy element]]; even if it does turn out to be an alkali metal, it is predicted to have some differences in physical and chemical properties from its lighter homologues. Most alkali metals have many different applications. One of the best-known applications of the pure elements is the use of rubidium and caesium in [[atomic clock]], of which caesium atomic clocks form the basis of the [[second]]. A common application of the compounds of sodium is the [[sodium-vapour lamp]], which emits light very efficiently. [[Salt|Table salt]], or sodium chloride, has been used since antiquity. [[Lithium (medication)|Lithium]] finds use as a psychiatric medication and as an [[anode]] in [[lithium batteries]]. Sodium and potassium are also [[essential element]], having major biological roles as [[electrolytes]], and although the other alkali metals are not essential, they also have various effects on the body, both beneficial and harmful. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"History"
]
| Sodium compounds have been known since ancient times; salt ([[sodium chloride]]) has been an important commodity in human activities, as testified by the English word ''salary'', referring to ''salarium'', money paid to Roman soldiers for the purchase of salt. While [[potash]] has been used since ancient times, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts. [[Georg Ernst Stahl]] obtained experimental evidence which led him to suggest the fundamental difference of sodium and potassium salts in 1702, and [[Henri-Louis Duhamel du Monceau]] was able to prove this difference in 1736. The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thus [[Antoine Lavoisier]] did not include either alkali in his list of chemical elements in 1789. Pure potassium was first isolated in 1807 in England by [[Humphry Davy]], who derived it from [[Potassium hydroxide|caustic potash]] (KOH, potassium hydroxide) by the use of electrolysis of the molten salt with the newly invented [[voltaic pile]]. Previous attempts at electrolysis of the aqueous salt were unsuccessful due to potassium's extreme reactivity. Potassium was the first metal that was isolated by electrolysis. Later that same year, Davy reported extraction of sodium from the similar substance [[caustic soda]] (NaOH, lye) by a similar technique, demonstrating the elements, and thus the salts, to be different. [[Petalite]] ([[Lithium|Li]] [[Aluminium|Al]] [[Silicon|Si]][[Oxygen|O]]) was discovered in 1800 by the [[Brazil]] chemist [[José Bonifácio de Andrada]] in a mine on the island of [[Utö, Sweden]]. However, it was not until 1817 that [[Johan August Arfwedson]], then working in the laboratory of the chemist [[Jöns Jacob Berzelius]], [[discovery of the chemical elements|detected]] the presence of a new element while analysing petalite [[ore]]. This new element was noted by him to form compounds similar to those of sodium and potassium, though its [[lithium carbonate|carbonate]] and [[lithium hydroxide|hydroxide]] were less [[solubility|soluble in water]] and more [[Base (chemistry)|alkaline]] than the other alkali metals. Berzelius gave the unknown material the name "''lithion''/''lithina''", from the [[Ancient Greek|Greek]] word ''λιθoς'' (transliterated as ''lithos'', meaning "stone"), to reflect its discovery in a solid mineral, as opposed to potassium, which had been discovered in plant ashes, and sodium, which was known partly for its high abundance in animal blood. He named the metal inside the material "''lithium''". Lithium, sodium, and potassium were part of the discovery of [[periodic table|periodicity]], as they are among a series of triads of elements in the same [[group (periodic table)|group]] that were noted by [[Johann Wolfgang Döbereiner]] in 1850 as having similar properties. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"History"
]
| Rubidium and caesium were the first elements to be discovered using the [[spectroscope]], invented in 1859 by [[Robert Bunsen]] and [[Gustav Kirchhoff]]. The next year, they discovered caesium in the [[mineral water]] from [[Bad Dürkheim]], Germany. Their discovery of rubidium came the following year in [[Heidelberg]], Germany, finding it in the mineral [[lepidolite]]. The names of rubidium and caesium come from the most prominent lines in their [[emission spectrum|emission spectra]]: a bright red line for rubidium (from the [[Latin]] word ''rubidus'', meaning dark red or bright red), and a sky-blue line for caesium (derived from the Latin word ''caesius'', meaning sky-blue). Around 1865 [[John Alexander Reina Newlands|John Newlands]] produced a series of papers where he listed the elements in order of increasing atomic weight and similar physical and chemical properties that recurred at intervals of eight; he likened such periodicity to the [[octave]] of music, where notes an octave apart have similar musical functions. His version put all the alkali metals then known (lithium to caesium), as well as [[copper]], [[silver]], and [[thallium]] (which show the +1 oxidation state characteristic of the alkali metals), together into a group. His table placed hydrogen with the [[halogen]]. After 1869, [[Dmitri Mendeleev]] proposed his periodic table placing lithium at the top of a group with sodium, potassium, rubidium, caesium, and thallium. Two years later, Mendeleev revised his table, placing hydrogen in group 1 above lithium, and also moving thallium to the [[boron group]]. In this 1871 version, copper, silver, and [[gold]] were placed twice, once as part of [[group 11 element|group IB]], and once as part of a "group VIII" encompassing today's groups [[group 8 element|8]] to 11. After the introduction of the 18-column table, the group IB elements were moved to their current position in the [[d-block]], while alkali metals were left in ''group IA''. Later the group's name was changed to ''group 1'' in 1988. The [[trivial name]] "alkali metals" comes from the fact that the hydroxides of the group 1 elements are all strong [[alkali]] when dissolved in water. There were at least four erroneous and incomplete discoveries before [[Marguerite Perey]] of the [[Curie Institute (Paris)|Curie Institute]] in Paris, France discovered francium in 1939 by purifying a sample of [[actinium-227]], which had been reported to have a decay energy of 220 [[electronvolt|keV]]. However, Perey noticed decay particles with an energy level below 80 keV. Perey thought this decay activity might have been caused by a previously unidentified decay product, one that was separated during purification, but emerged again out of the pure [[actinium]]-227. Various tests eliminated the possibility of the unknown element being [[thorium]], [[radium]], [[lead]], [[bismuth]], or [[thallium]]. The new product exhibited chemical properties of an alkali metal (such as coprecipitating with caesium salts), which led Perey to believe that it was element 87, caused by the [[alpha decay]] of actinium-227. Perey then attempted to determine the proportion of [[beta decay]] to alpha decay in actinium-227. Her first test put the alpha branching at 0.6%, a figure that she later revised to 1%. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"History"
]
| The next element below francium ([[Mendeleev's predicted elements|eka]]-francium) in the periodic table would be [[ununennium]] (Uue), element 119. The synthesis of ununennium was first attempted in 1985 by bombarding a target of [[einsteinium]]-254 with [[calcium]]-48 ions at the superHILAC accelerator at Berkeley, California. No atoms were identified, leading to a limiting yield of 300 [[barn (unit)|nb]]. + → * → ''no atoms'' It is highly unlikely that this reaction will be able to create any atoms of ununennium in the near future, given the extremely difficult task of making sufficient amounts of einsteinium-254, which is favoured for production of [[superheavy element|ultraheavy elements]] because of its large mass, relatively long half-life of 270 days, and availability in significant amounts of several micrograms, to make a large enough target to increase the sensitivity of the experiment to the required level; einsteinium has not been found in nature and has only been produced in laboratories, and in quantities smaller than those needed for effective synthesis of superheavy elements. However, given that ununennium is only the first [[period 8 element]] on the [[extended periodic table]], it may well be discovered in the near future through other reactions, and indeed an attempt to synthesise it is currently ongoing in Japan. Currently, none of the period 8 elements has been discovered yet, and it is also possible, due to [[nucleon drip line|drip instabilities]], that only the lower period 8 elements, up to around element 128, are physically possible. No attempts at synthesis have been made for any heavier alkali metals: due to their extremely high atomic number, they would require new, more powerful methods and technology to make. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Occurrence",
"In the Solar System"
]
| The [[Oddo–Harkins rule]] holds that elements with even atomic numbers are more common that those with odd atomic numbers, with the exception of hydrogen. This rule argues that elements with odd atomic numbers have one unpaired proton and are more likely to capture another, thus increasing their atomic number. In elements with even atomic numbers, protons are paired, with each member of the pair offsetting the spin of the other, enhancing stability. All the alkali metals have odd atomic numbers and they are not as common as the elements with even atomic numbers adjacent to them (the [[noble gas]] and the [[alkaline earth metal]]) in the Solar System. The heavier alkali metals are also less abundant than the lighter ones as the alkali metals from rubidium onward can only be synthesised in [[supernova]] and not in [[stellar nucleosynthesis]]. Lithium is also much less abundant than sodium and potassium as it is poorly synthesised in both [[Big Bang nucleosynthesis]] and in stars: the Big Bang could only produce trace quantities of lithium, [[beryllium]] and [[boron]] due to the absence of a stable nucleus with 5 or 8 [[nucleon]], and stellar nucleosynthesis could only pass this bottleneck by the [[triple-alpha process]], fusing three helium nuclei to form [[carbon]], and skipping over those three elements. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Occurrence",
"On Earth"
]
| The [[Earth]] formed from the same cloud of matter that formed the Sun, but the planets acquired different compositions during the [[formation and evolution of the solar system]]. In turn, the [[history of Earth|natural history of the Earth]] caused parts of this planet to have differing concentrations of the elements. The mass of the Earth is approximately 5.98 kg. It is composed mostly of [[iron]] (32.1%), [[oxygen]] (30.1%), [[silicon]] (15.1%), [[magnesium]] (13.9%), [[sulfur]] (2.9%), [[nickel]] (1.8%), [[calcium]] (1.5%), and [[aluminium]] (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to [[planetary differentiation]], the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements. The alkali metals, due to their high reactivity, do not occur naturally in pure form in nature. They are [[Goldschmidt classification|lithophiles]] and therefore remain close to the Earth's surface because they combine readily with [[oxygen]] and so associate strongly with [[silica]], forming relatively low-density minerals that do not sink down into the Earth's core. Potassium, rubidium and caesium are also [[incompatible element]] due to their large [[ionic radius|ionic radii]]. Sodium and potassium are very abundant in earth, both being among the ten [[abundance of elements in Earth's crust|most common elements in Earth's crust]]; sodium makes up approximately 2.6% of the [[Earth]]'s crust measured by weight, making it the [[Abundance of the chemical elements|sixth most abundant element]] overall and the most abundant alkali metal. Potassium makes up approximately 1.5% of the Earth's crust and is the seventh most abundant element. Sodium is found in many different minerals, of which the most common is ordinary salt (sodium chloride), which occurs in vast quantities dissolved in seawater. Other solid deposits include [[Halite (mineral)|halite]], [[amphibole]], [[cryolite]], [[nitratine]], and [[zeolite]]. Many of these solid deposits occur as a result of ancient seas evaporating, which still occurs now in places such as [[Utah]]'s [[Great Salt Lake]] and the [[Dead Sea]]. Despite their near-equal abundance in Earth's crust, sodium is far more common than potassium in the ocean, both because potassium's larger size makes its salts less soluble, and because potassium is bound by silicates in soil and what potassium leaches is absorbed far more readily by plant life than sodium. Despite its chemical similarity, lithium typically does not occur together with sodium or potassium due to its smaller size. Due to its relatively low reactivity, it can be found in seawater in large amounts; it is estimated that seawater is approximately 0.14 to 0.25 parts per million (ppm) or 25 [[micromolar]]. Its diagonal relationship with magnesium often allows it to replace magnesium in [[ferromagnesium]] minerals, where its crustal concentration is about 18 [[parts per million|ppm]], comparable to that of [[gallium]] and [[niobium]]. Commercially, the most important lithium mineral is [[spodumene]], which occurs in large deposits worldwide. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Occurrence",
"On Earth"
]
| Rubidium is approximately as abundant as [[zinc]] and more abundant than copper. It occurs naturally in the minerals [[leucite]], [[pollucite]], [[carnallite]], [[zinnwaldite]], and [[lepidolite]], although none of these contain only rubidium and no other alkali metals. Caesium is more abundant than some commonly known elements, such as [[antimony]], [[cadmium]], [[tin]], and [[tungsten]], but is much less abundant than rubidium. [[Francium-223]], the only naturally occurring isotope of francium, is the [[decay product|product]] of the [[alpha decay]] of actinium-227 and can be found in trace amounts in [[uranium]] minerals. In a given sample of uranium, there is estimated to be only one francium atom for every 10 uranium atoms. It has been calculated that there are at most 30 grams of francium in the [[crust (geology)|earth's crust]] at any time, due to its extremely short [[half-life]] of 22 minutes. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Properties",
"Physical and chemical"
]
| The physical and chemical properties of the alkali metals can be readily explained by their having an ns valence [[electron configuration]], which results in weak [[metallic bonding]]. Hence, all the alkali metals are soft and have low [[density|densities]], [[melting point|melting]] and [[boiling point]], as well as [[heat of sublimation|heats of sublimation]], [[heat of vaporization|vaporisation]], and [[dissociation (chemistry)|dissociation]]. They all crystallise in the [[body-centered cubic]] crystal structure, and have distinctive [[flame test|flame colours]] because their outer s electron is very easily excited. The ns configuration also results in the alkali metals having very large [[atomic radius|atomic]] and [[ionic radius|ionic radii]], as well as very high [[thermal conductivity|thermal]] and [[electrical conductivity]]. Their chemistry is dominated by the loss of their lone valence electron in the outermost s-orbital to form the +1 oxidation state, due to the ease of ionising this electron and the very high second ionisation energy. Most of the chemistry has been observed only for the first five members of the group. The chemistry of francium is not well established due to its extreme [[radioactive decay|radioactivity]]; thus, the presentation of its properties here is limited. What little is known about francium shows that it is very close in behaviour to caesium, as expected. The physical properties of francium are even sketchier because the bulk element has never been observed; hence any data that may be found in the literature are certainly speculative extrapolations. The alkali metals are more similar to each other than the elements in any other [[group (periodic table)|group]] are to each other. Indeed, the similarity is so great that it is quite difficult to separate potassium, rubidium, and caesium, due to their similar [[ionic radius|ionic radii]]; lithium and sodium are more distinct. For instance, when moving down the table, all known alkali metals show increasing [[atomic radius]], decreasing [[electronegativity]], increasing [[Reactivity (chemistry)|reactivity]], and decreasing melting and boiling points as well as heats of fusion and vaporisation. In general, their [[density|densities]] increase when moving down the table, with the exception that potassium is less dense than sodium. One of the very few properties of the alkali metals that does not display a very smooth trend is their [[reduction potential]]: lithium's value is anomalous, being more negative than the others. This is because the Li ion has a very high [[hydration energy]] in the gas phase: though the lithium ion disrupts the structure of water significantly, causing a higher change in entropy, this high hydration energy is enough to make the reduction potentials indicate it as being the most electropositive alkali metal, despite the difficulty of ionising it in the gas phase. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Properties",
"Physical and chemical"
]
| The stable alkali metals are all silver-coloured metals except for caesium, which has a pale golden tint: it is one of only three metals that are clearly coloured (the other two being copper and gold). Additionally, the heavy [[alkaline earth metal]] [[calcium]], [[strontium]], and [[barium]], as well as the divalent [[lanthanide]] [[europium]] and [[ytterbium]], are pale yellow, though the colour is much less prominent than it is for caesium. Their lustre tarnishes rapidly in air due to oxidation. They all crystallise in the [[body-centered cubic]] crystal structure, and have distinctive [[flame test|flame colours]] because their outer s electron is very easily excited. Indeed, these flame test colours are the most common way of identifying them since all their salts with common ions are soluble. All the alkali metals are highly reactive and are never found in elemental forms in nature. Because of this, they are usually stored in [[mineral oil]] or [[kerosene]] (paraffin oil). They react aggressively with the [[halogen]] to form the [[alkali metal halide]], which are white [[ionic crystal]] compounds that are all [[solubility|soluble]] in water except [[lithium fluoride]] ([[lithium|Li]] [[fluorine|F]]). The alkali metals also react with water to form strongly [[alkali]] [[hydroxide]] and thus should be handled with great care. The heavier alkali metals react more vigorously than the lighter ones; for example, when dropped into water, caesium produces a larger explosion than potassium if the same number of moles of each metal is used. The alkali metals have the lowest first [[ionization energy|ionisation energies]] in their respective periods of the [[periodic table]] because of their low [[effective nuclear charge]] and the ability to attain a [[noble gas]] configuration by losing just one [[electron]]. Not only do the alkali metals react with water, but also with proton donors like [[alcohol]] and [[phenols]], gaseous [[ammonia]], and [[alkyne]], the last demonstrating the phenomenal degree of their reactivity. Their great power as reducing agents makes them very useful in liberating other metals from their oxides or halides. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Properties",
"Physical and chemical"
]
| The second ionisation energy of all of the alkali metals is very high as it is in a full shell that is also closer to the nucleus; thus, they almost always lose a single electron, forming cations. The [[alkalide]] are an exception: they are unstable compounds which contain alkali metals in a −1 oxidation state, which is very unusual as before the discovery of the alkalides, the alkali metals were not expected to be able to form [[anion]] and were thought to be able to appear in [[salt (chemistry)|salts]] only as cations. The alkalide anions have filled [[s-orbital|s-subshells]], which gives them enough stability to exist. All the stable alkali metals except lithium are known to be able to form alkalides, and the alkalides have much theoretical interest due to their unusual [[stoichiometry]] and low [[ionization potential|ionisation potentials]]. Alkalides are chemically similar to the [[electride]], which are salts with trapped [[electron]] acting as anions. A particularly striking example of an alkalide is "inverse [[sodium hydride]]", HNa (both ions being [[coordination complex|complexed]]), as opposed to the usual sodium hydride, NaH: it is unstable in isolation, due to its high energy resulting from the displacement of two electrons from hydrogen to sodium, although several derivatives are predicted to be [[metastability|metastable]] or stable. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Properties",
"Physical and chemical"
]
| In aqueous solution, the alkali metal ions form [[metal ions in aqueous solution|aqua ions]] of the formula [M(HO)], where ''n'' is the solvation number. Their [[coordination number]] and shapes agree well with those expected from their ionic radii. In aqueous solution the water molecules directly attached to the metal ion are said to belong to the [[first coordination sphere]], also known as the first, or primary, solvation shell. The bond between a water molecule and the metal ion is a [[dative covalent bond]], with the oxygen atom donating both electrons to the bond. Each coordinated water molecule may be attached by [[hydrogen bond]] to other water molecules. The latter are said to reside in the second coordination sphere. However, for the alkali metal cations, the second coordination sphere is not well-defined as the +1 charge on the cation is not high enough to [[Polarizability|polarise]] the water molecules in the primary solvation shell enough for them to form strong hydrogen bonds with those in the second coordination sphere, producing a more stable entity. The solvation number for Li has been experimentally determined to be 4, forming the [[tetrahedron|tetrahedral]] [Li(HO)]: while solvation numbers of 3 to 6 have been found for lithium aqua ions, solvation numbers less than 4 may be the result of the formation of contact [[ion pair]], and the higher solvation numbers may be interpreted in terms of water molecules that approach [Li(HO)] through a face of the tetrahedron, though molecular dynamic simulations may indicate the existence of an [[octahedron|octahedral]] hexaaqua ion. There are also probably six water molecules in the primary solvation sphere of the sodium ion, forming the octahedral [Na(HO)] ion. While it was previously thought that the heavier alkali metals also formed octahedral hexaaqua ions, it has since been found that potassium and rubidium probably form the [K(HO)] and [Rb(HO)] ions, which have the [[square antiprism]] structure, and that caesium forms the 12-coordinate [Cs(HO)] ion. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Properties",
"Physical and chemical",
"Lithium"
]
| The chemistry of lithium shows several differences from that of the rest of the group as the small Li cation [[chemical polarity|polarises]] [[anion]] and gives its compounds a more [[covalent bond|covalent]] character. Lithium and [[magnesium]] have a [[diagonal relationship]] due to their similar atomic radii, so that they show some similarities. For example, lithium forms a stable [[nitride]], a property common among all the [[alkaline earth metal]] (magnesium's group) but unique among the alkali metals. In addition, among their respective groups, only lithium and magnesium form [[organometallic compound]] with significant covalent character (e.g. Li[[methyl group|Me]] and MgMe). Lithium fluoride is the only alkali metal halide that is poorly soluble in water, and [[lithium hydroxide]] is the only alkali metal hydroxide that is not [[deliquescent]]. Conversely, [[lithium perchlorate]] and other lithium salts with large anions that cannot be polarised are much more stable than the analogous compounds of the other alkali metals, probably because Li has a high [[solvation energy]]. This effect also means that most simple lithium salts are commonly encountered in hydrated form, because the anhydrous forms are extremely [[hygroscopic]]: this allows salts like [[lithium chloride]] and [[lithium bromide]] to be used in [[dehumidifier]] and [[air-conditioner]]. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Properties",
"Physical and chemical",
"Francium"
]
| Francium is also predicted to show some differences due to its high [[atomic weight]], causing its electrons to travel at considerable fractions of the speed of light and thus making [[relativistic quantum chemistry|relativistic effects]] more prominent. In contrast to the trend of decreasing [[electronegativity|electronegativities]] and [[ionisation energy|ionisation energies]] of the alkali metals, francium's electronegativity and ionisation energy are predicted to be higher than caesium's due to the relativistic stabilisation of the 7s electrons; also, its [[atomic radius]] is expected to be abnormally low. Thus, contrary to expectation, caesium is the most reactive of the alkali metals, not francium. All known physical properties of francium also deviate from the clear trends going from lithium to caesium, such as the first ionisation energy, electron affinity, and anion polarisability, though due to the paucity of known data about francium many sources give extrapolated values, ignoring that relativistic effects make the trend from lithium to caesium become inapplicable at francium. Some of the few properties of francium that have been predicted taking relativity into account are the electron affinity (47.2 kJ/mol) and the enthalpy of dissociation of the Fr molecule (42.1 kJ/mol). The CsFr molecule is polarised as CsFr, showing that the 7s subshell of francium is much more strongly affected by relativistic effects than the 6s subshell of caesium. Additionally, francium superoxide (FrO) is expected to have significant covalent character, unlike the other alkali metal superoxides, because of bonding contributions from the 6p electrons of francium. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Properties",
"Nuclear"
]
| All the alkali metals have odd atomic numbers; hence, their isotopes must be either [[odd–odd nuclei|odd–odd]] (both proton and [[neutron number]] are odd) or [[odd–even nuclei|odd–even]] ([[proton number]] is odd, but neutron number is even). Odd–odd nuclei have even [[mass number]], whereas odd–even nuclei have odd mass numbers. Odd–odd [[primordial nuclide]] are rare because most odd–odd nuclei are highly unstable with respect to [[beta decay]], because the decay products are even–even, and are therefore more strongly bound, due to [[Semi-empirical mass formula#Pairing term|nuclear pairing effects]]. Due to the great rarity of odd–odd nuclei, almost all the primordial isotopes of the alkali metals are odd–even (the exceptions being the light stable isotope lithium-6 and the long-lived [[radioisotope]] potassium-40). For a given odd mass number, there can be only a single [[beta-decay stable isobars|beta-stable nuclide]], since there is not a difference in binding energy between even–odd and odd–even comparable to that between even–even and odd–odd, leaving other nuclides of the same mass number ([[isobar (nuclide)|isobars]]) free to [[beta decay]] toward the lowest-mass nuclide. An effect of the instability of an odd number of either type of nucleons is that odd-numbered elements, such as the alkali metals, tend to have fewer stable isotopes than even-numbered elements. Of the 26 [[monoisotopic element]] that have only a single stable isotope, all but one have an odd atomic number and all but one also have an even number of neutrons. [[Beryllium]] is the single exception to both rules, due to its low atomic number. All of the alkali metals except lithium and caesium have at least one naturally occurring [[radioisotope]]: [[sodium-22]] and [[sodium-24]] are [[trace radioisotope]] produced [[cosmogenic]], potassium-40 and [[rubidium-87]] have very long [[half-life|half-lives]] and thus occur naturally, and all [[isotopes of francium]] are [[radioactive decay|radioactive]]. Caesium was also thought to be radioactive in the early 20th century, although it has no naturally occurring radioisotopes. (Francium had not been discovered yet at that time.) The natural long-lived radioisotope of potassium, potassium-40, makes up about 0.012% of natural potassium, and thus natural potassium is weakly radioactive. This natural radioactivity became a basis for a mistaken claim of the discovery for element 87 (the next alkali metal after caesium) in 1925. Natural rubidium is similarly slightly radioactive, with 27.83% being the long-lived radioisotope rubidium-87. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Properties",
"Nuclear"
]
| [[Caesium-137]], with a half-life of 30.17 years, is one of the two principal [[medium-lived fission product]], along with [[strontium-90]], which are responsible for most of the [[radioactivity]] of [[spent nuclear fuel]] after several years of cooling, up to several hundred years after use. It constitutes most of the radioactivity still left from the [[Chernobyl accident]]. Caesium-137 undergoes high-energy beta decay and eventually becomes stable [[barium-137]]. It is a strong emitter of gamma radiation. Caesium-137 has a very low rate of neutron capture and cannot be feasibly disposed of in this way, but must be allowed to decay. Caesium-137 has been used as a [[Flow tracer|tracer]] in hydrologic studies, analogous to the use of [[tritium]]. Small amounts of [[caesium-134]] and caesium-137 were released into the environment during nearly all [[nuclear weapon test]] and some [[nuclear accident]], most notably the [[Goiânia accident]] and the [[Chernobyl disaster]]. As of 2005, caesium-137 is the principal source of radiation in the [[zone of alienation]] around the [[Chernobyl nuclear power plant]]. Its chemical properties as one of the alkali metals make it one of most problematic of the short-to-medium-lifetime fission products because it easily moves and spreads in nature due to the high water solubility of its salts, and is taken up by the body, which mistakes it for its essential congeners sodium and potassium. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Periodic trends"
]
| The alkali metals are more similar to each other than the elements in any other [[group (periodic table)|group]] are to each other. For instance, when moving down the table, all known alkali metals show increasing [[atomic radius]], decreasing [[electronegativity]], increasing [[reactivity (chemistry)|reactivity]], and decreasing melting and boiling points as well as heats of fusion and vaporisation. In general, their [[density|densities]] increase when moving down the table, with the exception that potassium is less dense than sodium. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Periodic trends",
"Atomic and ionic radii"
]
| The atomic radii of the alkali metals increase going down the group. Because of the [[shielding effect]], when an atom has more than one [[electron shell]], each electron feels electric repulsion from the other electrons as well as electric attraction from the nucleus. In the alkali metals, the [[valence electron|outermost electron]] only feels a net charge of +1, as some of the [[nuclear charge]] (which is equal to the [[atomic number]]) is cancelled by the inner electrons; the number of inner electrons of an alkali metal is always one less than the nuclear charge. Therefore, the only factor which affects the atomic radius of the alkali metals is the number of electron shells. Since this number increases down the group, the atomic radius must also increase down the group. The [[ionic radius|ionic radii]] of the alkali metals are much smaller than their atomic radii. This is because the outermost electron of the alkali metals is in a different [[electron shell]] than the inner electrons, and thus when it is removed the resulting atom has one fewer electron shell and is smaller. Additionally, the [[effective nuclear charge]] has increased, and thus the electrons are attracted more strongly towards the nucleus and the ionic radius decreases. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Periodic trends",
"First ionisation energy"
]
| The first ionisation energy of an [[chemical element|element]] or [[molecule]] is the energy required to move the most loosely held electron from one [[mole (unit)|mole]] of gaseous atoms of the element or molecules to form one mole of gaseous ions with [[electric charge]] +1. The factors affecting the first ionisation energy are the [[nuclear charge]], the amount of [[shielding effect|shielding]] by the inner electrons and the distance from the most loosely held electron from the nucleus, which is always an outer electron in [[main group element]]. The first two factors change the effective nuclear charge the most loosely held electron feels. Since the outermost electron of alkali metals always feels the same effective nuclear charge (+1), the only factor which affects the first ionisation energy is the distance from the outermost electron to the nucleus. Since this distance increases down the group, the outermost electron feels less attraction from the nucleus and thus the first ionisation energy decreases. (This trend is broken in francium due to the [[relativistic quantum chemistry|relativistic]] stabilisation and contraction of the 7s orbital, bringing francium's valence electron closer to the nucleus than would be expected from non-relativistic calculations. This makes francium's outermost electron feel more attraction from the nucleus, increasing its first ionisation energy slightly beyond that of caesium.) The second ionisation energy of the alkali metals is much higher than the first as the second-most loosely held electron is part of a fully filled [[electron shell]] and is thus difficult to remove. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Periodic trends",
"Reactivity"
]
| The reactivities of the alkali metals increase going down the group. This is the result of a combination of two factors: the first ionisation energies and [[atomisation energy|atomisation energies]] of the alkali metals. Because the first ionisation energy of the alkali metals decreases down the group, it is easier for the outermost electron to be removed from the atom and participate in [[chemical reaction]], thus increasing reactivity down the group. The atomisation energy measures the strength of the [[metallic bond]] of an element, which falls down the group as the atoms increase in [[atomic radius|radius]] and thus the metallic bond must increase in length, making the [[delocalized electron|delocalised electrons]] further away from the attraction of the nuclei of the heavier alkali metals. Adding the atomisation and first ionisation energies gives a quantity closely related to (but not equal to) the [[activation energy]] of the reaction of an alkali metal with another substance. This quantity decreases going down the group, and so does the activation energy; thus, chemical reactions can occur faster and the reactivity increases down the group. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Periodic trends",
"Electronegativity"
]
| Electronegativity is a [[chemical property]] that describes the tendency of an [[atom]] or a [[functional group]] to attract [[electron]] (or [[electron density]]) towards itself. If the bond between [[sodium]] and [[chlorine]] in [[sodium chloride]] were [[covalent bond|covalent]], the pair of shared electrons would be attracted to the chlorine because the effective nuclear charge on the outer electrons is +7 in chlorine but is only +1 in sodium. The electron pair is attracted so close to the chlorine atom that they are practically transferred to the chlorine atom (an [[ionic bond]]). However, if the sodium atom was replaced by a lithium atom, the electrons will not be attracted as close to the chlorine atom as before because the lithium atom is smaller, making the electron pair more strongly attracted to the closer effective nuclear charge from lithium. Hence, the larger alkali metal atoms (further down the group) will be less electronegative as the bonding pair is less strongly attracted towards them. As mentioned previously, francium is expected to be an exception. Because of the higher electronegativity of lithium, some of its compounds have a more covalent character. For example, [[lithium iodide]] ([[lithium|Li]] [[iodine|I]]) will dissolve in [[organic solvent]], a property of most covalent compounds. [[Lithium fluoride]] (Li[[fluorine|F]]) is the only [[alkali halide]] that is not soluble in water, and [[lithium hydroxide]] (Li[[hydroxide|OH]]) is the only [[alkali hydroxide|alkali metal hydroxide]] that is not [[deliquescent]]. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Periodic trends",
"Melting and boiling points"
]
| The melting point of a substance is the point where it changes [[state of matter|state]] from [[solid]] to [[liquid]] while the boiling point of a substance (in liquid state) is the point where the [[vapor pressure|vapour pressure]] of the liquid equals the environmental pressure surrounding the liquid and all the liquid changes state to [[gas]]. As a metal is heated to its melting point, the [[metallic bond]] keeping the atoms in place weaken so that the atoms can move around, and the metallic bonds eventually break completely at the metal's boiling point. Therefore, the falling melting and boiling points of the alkali metals indicate that the strength of the metallic bonds of the alkali metals decreases down the group. This is because metal atoms are held together by the electromagnetic attraction from the positive ions to the delocalised electrons. As the atoms increase in size going down the group (because their atomic radius increases), the nuclei of the ions move further away from the delocalised electrons and hence the metallic bond becomes weaker so that the metal can more easily melt and boil, thus lowering the melting and boiling points. (The increased nuclear charge is not a relevant factor due to the shielding effect.) | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Periodic trends",
"Density"
]
| The alkali metals all have the same [[crystal structure]] ([[body-centered cubic|body-centred cubic]]) and thus the only relevant factors are the number of atoms that can fit into a certain volume and the mass of one of the atoms, since density is defined as mass per unit volume. The first factor depends on the volume of the atom and thus the atomic radius, which increases going down the group; thus, the volume of an alkali metal atom increases going down the group. The mass of an alkali metal atom also increases going down the group. Thus, the trend for the densities of the alkali metals depends on their atomic weights and atomic radii; if figures for these two factors are known, the ratios between the densities of the alkali metals can then be calculated. The resultant trend is that the densities of the alkali metals increase down the table, with an exception at potassium. Due to having the lowest atomic weight and the largest atomic radius of all the elements in their periods, the alkali metals are the least dense metals in the periodic table. Lithium, sodium, and potassium are the only three metals in the periodic table that are less dense than water: in fact, lithium is the least dense known solid at [[room temperature]]. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Compounds"
]
| The alkali metals form complete series of compounds with all usually encountered anions, which well illustrate group trends. These compounds can be described as involving the alkali metals losing electrons to acceptor species and forming monopositive ions. This description is most accurate for alkali halides and becomes less and less accurate as cationic and anionic charge increase, and as the anion becomes larger and more polarisable. For instance, [[ionic bond]] gives way to [[metallic bond]] along the series NaCl, NaO, NaS, NaP, NaAs, NaSb, NaBi, Na. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Compounds",
"Hydroxides"
]
| All the alkali metals react vigorously or explosively with cold water, producing an [[aqueous solution]] of a strongly [[base (chemistry)|basic]] alkali metal [[hydroxide]] and releasing hydrogen gas. This reaction becomes more vigorous going down the group: lithium reacts steadily with [[effervescence]], but sodium and potassium can ignite and rubidium and caesium sink in water and generate hydrogen gas so rapidly that shock waves form in the water that may shatter glass containers. When an alkali metal is dropped into water, it produces an explosion, of which there are two separate stages. The metal reacts with the water first, breaking the hydrogen bonds in the water and producing [[hydrogen]] gas; this takes place faster for the more reactive heavier alkali metals. Second, the heat generated by the first part of the reaction often ignites the hydrogen gas, causing it to burn explosively into the surrounding air. This secondary hydrogen gas explosion produces the visible flame above the bowl of water, lake or other body of water, not the initial reaction of the metal with water (which tends to happen mostly under water). The alkali metal hydroxides are the most basic known hydroxides. Recent research has suggested that the explosive behavior of alkali metals in water is driven by a [[Coulomb explosion]] rather than solely by rapid generation of hydrogen itself. All alkali metals melt as a part of the reaction with water. Water molecules ionise the bare metallic surface of the liquid metal, leaving a positively charged metal surface and negatively charged water ions. The attraction between the charged metal and water ions will rapidly increase the surface area, causing an exponential increase of ionisation. When the repulsive forces within the liquid metal surface exceeds the forces of the surface tension, it vigorously explodes. The hydroxides themselves are the most basic hydroxides known, reacting with acids to give salts and with alcohols to give [[oligomer]] [[alkoxide]]. They easily react with [[carbon dioxide]] to form [[carbonate]] or [[bicarbonate]], or with [[hydrogen sulfide]] to form [[sulfide]] or [[bisulfide]], and may be used to separate [[thiol]] from petroleum. They react with amphoteric oxides: for example, the oxides of [[aluminium oxide|aluminium]], [[zinc oxide|zinc]], [[tin(IV) oxide| tin]], and [[lead dioxide|lead]] react with the alkali metal hydroxides to give aluminates, zincates, stannates, and plumbates. [[Silicon dioxide]] is acidic, and thus the alkali metal hydroxides can also attack [[silicate glass]]. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Compounds",
"Intermetallic compounds"
]
| The alkali metals form many [[intermetallic compound]] with each other and the elements from groups [[alkaline earth metal|2]] to [[boron group|13]] in the periodic table of varying stoichiometries, such as the [[sodium amalgam]] with [[mercury (element)|mercury]], including NaHg and NaHg. Some of these have ionic characteristics: taking the alloys with [[gold]], the most electronegative of metals, as an example, NaAu and KAu are metallic, but RbAu and [[caesium auride|CsAu]] are semiconductors. [[NaK]] is an alloy of sodium and potassium that is very useful because it is liquid at room temperature, although precautions must be taken due to its extreme reactivity towards water and air. The [[eutectic mixture]] melts at −12.6 °C. An alloy of 41% caesium, 47% sodium, and 12% potassium has the lowest known melting point of any metal or alloy, −78 °C. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Compounds",
"Compounds with the group 13 elements"
]
| The intermetallic compounds of the alkali metals with the heavier group 13 elements ([[aluminium]], [[gallium]], [[indium]], and [[thallium]]), such as NaTl, are poor [[Electrical conductor|conductors]] or [[semiconductor]], unlike the normal alloys with the preceding elements, implying that the alkali metal involved has lost an electron to the [[Zintl phase|Zintl anions]] involved. Nevertheless, while the elements in group 14 and beyond tend to form discrete anionic clusters, group 13 elements tend to form polymeric ions with the alkali metal cations located between the giant ionic lattice. For example, NaTl consists of a polymeric anion (—Tl—) with a covalent [[diamond cubic]] structure with Na ions located between the anionic lattice. The larger alkali metals cannot fit similarly into an anionic lattice and tend to force the heavier group 13 elements to form anionic clusters. [[Boron]] is a special case, being the only nonmetal in group 13. The alkali metal [[boride]] tend to be boron-rich, involving appreciable boron–boron bonding involving [[deltahedron|deltahedral]] structures, and are thermally unstable due to the alkali metals having a very high [[vapour pressure]] at elevated temperatures. This makes direct synthesis problematic because the alkali metals do not react with boron below 700 °C, and thus this must be accomplished in sealed containers with the alkali metal in excess. Furthermore, exceptionally in this group, reactivity with boron decreases down the group: lithium reacts completely at 700 °C, but sodium at 900 °C and potassium not until 1200 °C, and the reaction is instantaneous for lithium but takes hours for potassium. Rubidium and caesium borides have not even been characterised. Various phases are known, such as LiB, NaB, NaB, and KB. Under high pressure the boron–boron bonding in the lithium borides changes from following [[polyhedral skeletal electron pair theory|Wade's rules]] to forming Zintl anions like the rest of group 13. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Compounds",
"Compounds with the group 14 elements"
]
| Lithium and sodium react with [[carbon]] to form [[acetylide]], LiC and NaC, which can also be obtained by reaction of the metal with [[acetylene]]. Potassium, rubidium, and caesium react with [[graphite]]; their atoms are [[intercalation (chemistry)|intercalated]] between the hexagonal graphite layers, forming [[graphite intercalation compound]] of formulae MC (dark grey, almost black), MC (dark grey, almost black), MC (blue), MC (steel blue), and MC (bronze) (M = K, Rb, or Cs). These compounds are over 200 times more electrically conductive than pure graphite, suggesting that the valence electron of the alkali metal is transferred to the graphite layers (e.g. ). Upon heating of KC, the elimination of potassium atoms results in the conversion in sequence to KC, KC, KC and finally KC. KC is a very strong [[reducing agent]] and is pyrophoric and explodes on contact with water. While the larger alkali metals (K, Rb, and Cs) initially form MC, the smaller ones initially form MC, and indeed they require reaction of the metals with graphite at high temperatures around 500 °C to form. Apart from this, the alkali metals are such strong reducing agents that they can even reduce [[buckminsterfullerene]] to produce solid [[fullerides]] MC; sodium, potassium, rubidium, and caesium can form fullerides where ''n'' = 2, 3, 4, or 6, and rubidium and caesium additionally can achieve ''n'' = 1. When the alkali metals react with the heavier elements in the [[carbon group]] ([[silicon]], [[germanium]], [[tin]], and [[lead]]), ionic substances with cage-like structures are formed, such as the [[silicide]] M[[silicon|Si]] (M = K, Rb, or Cs), which contains M and tetrahedral ions. The chemistry of alkali metal [[germanide]], involving the germanide ion [[germanium|Ge]] and other cluster ([[Zintl ion|Zintl]]) ions such as , , , and [(Ge)], is largely analogous to that of the corresponding silicides. Alkali metal [[stannide]] are mostly ionic, sometimes with the stannide ion ([[tin|Sn]]), and sometimes with more complex Zintl ions such as , which appears in tetrapotassium nonastannide (KSn). The monatomic [[plumbide]] ion ([[lead|Pb]]) is unknown, and indeed its formation is predicted to be energetically unfavourable; alkali metal plumbides have complex Zintl ions, such as . These alkali metal germanides, stannides, and plumbides may be produced by reducing germanium, tin, and lead with sodium metal in liquid ammonia. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Compounds",
"Nitrides and pnictides"
]
| Lithium, the lightest of the alkali metals, is the only alkali metal which reacts with [[nitrogen]] at [[standard conditions]], and its [[nitride]] is the only stable alkali metal nitride. Nitrogen is an [[reactivity (chemistry)|unreactive]] gas because breaking the strong [[triple bond]] in the [[dinitrogen]] molecule (N) requires a lot of energy. The formation of an alkali metal nitride would consume the ionisation energy of the alkali metal (forming M ions), the energy required to break the triple bond in N and the formation of N ions, and all the energy released from the formation of an alkali metal nitride is from the [[lattice energy]] of the alkali metal nitride. The lattice energy is maximised with small, highly charged ions; the alkali metals do not form highly charged ions, only forming ions with a charge of +1, so only lithium, the smallest alkali metal, can release enough lattice energy to make the reaction with nitrogen [[exothermic]], forming [[lithium nitride]]. The reactions of the other alkali metals with nitrogen would not release enough lattice energy and would thus be [[endothermic]], so they do not form nitrides at standard conditions. [[Sodium nitride]] (NaN) and [[potassium nitride]] (KN), while existing, are extremely unstable, being prone to decomposing back into their constituent elements, and cannot be produced by reacting the elements with each other at standard conditions. Steric hindrance forbids the existence of rubidium or caesium nitride. However, sodium and potassium form colourless [[azide]] salts involving the linear anion; due to the large size of the alkali metal cations, they are thermally stable enough to be able to melt before decomposing. All the alkali metals react readily with [[phosphorus]] and [[arsenic]] to form phosphides and arsenides with the formula MPn (where M represents an alkali metal and Pn represents a [[pnictogen]] – phosphorus, arsenic, [[antimony]], or [[bismuth]]). This is due to the greater size of the P and As ions, so that less lattice energy needs to be released for the salts to form. These are not the only phosphides and arsenides of the alkali metals: for example, potassium has nine different known phosphides, with formulae KP, KP, KP, KP, KP, KP, KP, KP, and KP. While most metals form arsenides, only the alkali and alkaline earth metals form mostly ionic arsenides. The structure of NaAs is complex with unusually short Na–Na distances of 328–330 pm which are shorter than in sodium metal, and this indicates that even with these electropositive metals the bonding cannot be straightforwardly ionic. Other alkali metal arsenides not conforming to the formula MAs are known, such as LiAs, which has a metallic lustre and electrical conductivity indicating the presence of some [[metallic bond]]. The [[antimonide]] are unstable and reactive as the [[antimony|Sb]] ion is a strong reducing agent; reaction of them with acids form the toxic and unstable gas [[stibine]] (SbH). Indeed, they have some metallic properties, and the alkali metal antimonides of stoichiometry MSb involve antimony atoms bonded in a spiral Zintl structure. [[Bismuth]] are not even wholly ionic; they are [[intermetallic compound]] containing partially metallic and partially ionic bonds. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
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[
"Compounds",
"Oxides and chalcogenides"
]
| All the alkali metals react vigorously with [[oxygen]] at standard conditions. They form various types of oxides, such as simple [[oxide]] (containing the O ion), [[peroxide]] (containing the ion, where there is a [[single bond]] between the two oxygen atoms), [[superoxide]] (containing the ion), and many others. Lithium burns in air to form [[lithium oxide]], but sodium reacts with oxygen to form a mixture of [[sodium oxide]] and [[sodium peroxide]]. Potassium forms a mixture of [[potassium peroxide]] and [[potassium superoxide]], while rubidium and caesium form the superoxide exclusively. Their reactivity increases going down the group: while lithium, sodium and potassium merely burn in air, rubidium and caesium are [[pyrophoric]] (spontaneously catch fire in air). The smaller alkali metals tend to polarise the larger anions (the peroxide and superoxide) due to their small size. This attracts the electrons in the more complex anions towards one of its constituent oxygen atoms, forming an oxide ion and an oxygen atom. This causes lithium to form the oxide exclusively on reaction with oxygen at room temperature. This effect becomes drastically weaker for the larger sodium and potassium, allowing them to form the less stable peroxides. Rubidium and caesium, at the bottom of the group, are so large that even the least stable superoxides can form. Because the superoxide releases the most energy when formed, the superoxide is preferentially formed for the larger alkali metals where the more complex anions are not polarised. (The oxides and peroxides for these alkali metals do exist, but do not form upon direct reaction of the metal with oxygen at standard conditions.) In addition, the small size of the Li and O ions contributes to their forming a stable ionic lattice structure. Under controlled conditions, however, all the alkali metals, with the exception of francium, are known to form their oxides, peroxides, and superoxides. The alkali metal peroxides and superoxides are powerful [[oxidising agent]]. [[Sodium peroxide]] and [[potassium superoxide]] react with [[carbon dioxide]] to form the alkali metal carbonate and oxygen gas, which allows them to be used in [[submarine]] air purifiers; the presence of [[water vapour]], naturally present in breath, makes the removal of carbon dioxide by potassium superoxide even more efficient. All the stable alkali metals except lithium can form red [[ozonide]] (MO) through low-temperature reaction of the powdered anhydrous hydroxide with [[ozone]]: the ozonides may be then extracted using liquid [[ammonia]]. They slowly decompose at standard conditions to the superoxides and oxygen, and hydrolyse immediately to the hydroxides when in contact with water. Potassium, rubidium, and caesium also form sesquioxides MO, which may be better considered peroxide disuperoxides, . Rubidium and caesium can form a great variety of suboxides with the metals in formal oxidation states below +1. Rubidium can form RbO and RbO (copper-coloured) upon oxidation in air, while caesium forms an immense variety of oxides, such as the ozonide CsO and several brightly coloured [[suboxide]], such as CsO (bronze), CsO (red-violet), CsO (violet), CsO (dark green), CsO, CsO, as well as CsO. The last of these may be heated under vacuum to generate CsO. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
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[
"Compounds",
"Oxides and chalcogenides"
]
| The alkali metals can also react analogously with the heavier chalcogens ([[sulfur]], [[selenium]], [[tellurium]], and [[polonium]]), and all the alkali metal chalcogenides are known (with the exception of francium's). Reaction with an excess of the chalcogen can similarly result in lower chalcogenides, with chalcogen ions containing chains of the chalcogen atoms in question. For example, sodium can react with sulfur to form the [[sulfide]] ([[sodium sulfide|NaS]]) and various [[polysulfide]] with the formula NaS (''x'' from 2 to 6), containing the ions. Due to the basicity of the Se and Te ions, the alkali metal [[selenide]] and [[telluride (chemistry)|tellurides]] are alkaline in solution; when reacted directly with selenium and tellurium, alkali metal polyselenides and polytellurides are formed along with the selenides and tellurides with the and ions. They may be obtained directly from the elements in liquid ammonia or when air is not present, and are colourless, water-soluble compounds that air oxidises quickly back to selenium or tellurium. The alkali metal [[polonide]] are all ionic compounds containing the Po ion; they are very chemically stable and can be produced by direct reaction of the elements at around 300–400 °C. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
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[
"Compounds",
"Halides, hydrides, and pseudohalides"
]
| The alkali metals are among the most [[electropositive]] elements on the periodic table and thus tend to [[ionic bond|bond ionically]] to the most [[electronegative]] elements on the periodic table, the [[halogen]] ([[fluorine]], [[chlorine]], [[bromine]], [[iodine]], and [[astatine]]), forming [[salt (chemistry)|salts]] known as the alkali metal halides. The reaction is very vigorous and can sometimes result in explosions. All twenty stable alkali metal halides are known; the unstable ones are not known, with the exception of sodium astatide, because of the great instability and rarity of astatine and francium. The most well-known of the twenty is certainly [[sodium chloride]], otherwise known as common salt. All of the stable alkali metal halides have the formula MX where M is an alkali metal and X is a halogen. They are all white ionic crystalline solids that have high melting points. All the alkali metal halides are [[solubility|soluble]] in water except for [[lithium fluoride]] (LiF), which is insoluble in water due to its very high [[lattice enthalpy]]. The high lattice enthalpy of lithium fluoride is due to the small sizes of the Li and F ions, causing the [[electrostatic interaction]] between them to be strong: a similar effect occurs for [[magnesium fluoride]], consistent with the diagonal relationship between lithium and magnesium. The alkali metals also react similarly with hydrogen to form ionic alkali metal hydrides, where the [[hydride]] anion acts as a [[pseudohalogen|pseudohalide]]: these are often used as reducing agents, producing hydrides, complex metal hydrides, or hydrogen gas. Other pseudohalides are also known, notably the [[cyanide]]. These are isostructural to the respective halides except for [[lithium cyanide]], indicating that the cyanide ions may rotate freely. Ternary alkali metal halide oxides, such as NaClO, KBrO (yellow), NaBrO, NaIO, and KBrO, are also known. The polyhalides are rather unstable, although those of rubidium and caesium are greatly stabilised by the feeble polarising power of these extremely large cations. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
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[
"Compounds",
"Coordination complexes"
]
| Alkali metal cations do not usually form [[coordination complex]] with simple [[Lewis base]] due to their low charge of just +1 and their relatively large size; thus the Li ion forms most complexes and the heavier alkali metal ions form less and less (though exceptions occur for weak complexes). Lithium in particular has a very rich coordination chemistry in which it exhibits [[coordination number]] from 1 to 12, although octahedral hexacoordination is its preferred mode. In [[aqueous solution]], the alkali metal ions exist as octahedral hexahydrate complexes ([M(HO))]), with the exception of the lithium ion, which due to its small size forms tetrahedral tetrahydrate complexes ([Li(HO))]); the alkali metals form these complexes because their ions are attracted by electrostatic forces of attraction to the polar water molecules. Because of this, [[anhydrous]] salts containing alkali metal cations are often used as [[desiccant]]. Alkali metals also readily form complexes with [[crown ether]] (e.g. [[12-crown-4]] for Li, [[15-crown-5]] for Na, [[18-crown-6]] for K, and [[21-crown-7]] for Rb) and [[cryptand]] due to electrostatic attraction. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
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[
"Compounds",
"Ammonia solutions"
]
| The alkali metals dissolve slowly in liquid [[ammonia]], forming ammoniacal solutions of solvated metal cation M and [[solvated electron]] e, which react to form hydrogen gas and the [[metal amide#Alkali metal amides|alkali metal amide]] (MNH, where M represents an alkali metal): this was first noted by [[Humphry Davy]] in 1809 and rediscovered by W. Weyl in 1864. The process may be speeded up by a [[catalyst]]. Similar solutions are formed by the heavy divalent [[alkaline earth metal]] [[calcium]], [[strontium]], [[barium]], as well as the divalent [[lanthanide]], [[europium]] and [[ytterbium]]. The amide salt is quite insoluble and readily precipitates out of solution, leaving intensely coloured ammonia solutions of the alkali metals. In 1907, Charles Krause identified the colour as being due to the presence of [[solvated electron]], which contribute to the high electrical conductivity of these solutions. At low concentrations (below 3 M), the solution is dark blue and has ten times the conductivity of aqueous [[sodium chloride]]; at higher concentrations (above 3 M), the solution is copper-coloured and has approximately the conductivity of liquid metals like [[mercury (element)|mercury]]. In addition to the alkali metal amide salt and solvated electrons, such ammonia solutions also contain the alkali metal cation (M), the neutral alkali metal atom (M), [[diatomic molecule|diatomic]] alkali metal molecules (M) and alkali metal anions (M). These are unstable and eventually become the more thermodynamically stable alkali metal amide and hydrogen gas. Solvated electrons are powerful [[reducing agent]] and are often used in chemical synthesis. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
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[
"Compounds",
"Organometallic",
"Organolithium"
]
| Being the smallest alkali metal, lithium forms the widest variety of and most stable [[organometallic compound]], which are bonded covalently. [[Organolithium reagent|Organolithium]] compounds are electrically non-conducting volatile solids or liquids that melt at low temperatures, and tend to form [[oligomer]] with the structure (RLi) where R is the organic group. As the electropositive nature of lithium puts most of the [[charge density]] of the bond on the carbon atom, effectively creating a [[carbanion]], organolithium compounds are extremely powerful [[base (chemistry)|bases]] and [[carbon nucleophile|nucleophiles]]. For use as bases, [[butyllithium]] are often used and are commercially available. An example of an organolithium compound is [[methyllithium]] ((CHLi)), which exists in tetrameric (''x'' = 4, tetrahedral) and hexameric (''x'' = 6, octahedral) forms. Organolithium compounds, especially ''n''-butyllithium, are useful reagents in organic synthesis, as might be expected given lithium's diagonal relationship with magnesium, which plays an important role in the [[Grignard reaction]]. For example, alkyllithiums and aryllithiums may be used to synthesise [[aldehyde]] and [[ketone]] by reaction with metal [[carbonyl]]. The reaction with [[nickel tetracarbonyl]], for example, proceeds through an unstable acyl nickel carbonyl complex which then undergoes [[electrophilic substitution]] to give the desired aldehyde (using H as the electrophile) or ketone (using an alkyl halide) product. LiR + [Ni(CO)] Li[RCONi(CO)] Li[RCONi(CO)] Li + RCHO + [(solvent)Ni(CO)] Li[RCONi(CO)] Li + R'COR + [(solvent)Ni(CO)] Alkyllithiums and aryllithiums may also react with ''N'',''N''-disubstituted [[amide]] to give aldehydes and ketones, and symmetrical ketones by reacting with [[carbon monoxide]]. They thermally decompose to eliminate a β-hydrogen, producing [[alkene]] and [[lithium hydride]]: another route is the reaction of [[ether]] with alkyl- and aryllithiums that act as strong bases. In non-polar solvents, aryllithiums react as the carbanions they effectively are, turning carbon dioxide to aromatic [[carboxylic acid]] (ArCOH) and aryl ketones to tertiary carbinols (Ar'C(Ar)OH). Finally, they may be used to synthesise other organometallic compounds through metal-halogen exchange. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
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[
"Compounds",
"Organometallic",
"Heavier alkali metals"
]
| Unlike the organolithium compounds, the organometallic compounds of the heavier alkali metals are predominantly ionic. The application of [[organosodium chemistry|organosodium]] compounds in chemistry is limited in part due to competition from [[organolithium compound]], which are commercially available and exhibit more convenient reactivity. The principal organosodium compound of commercial importance is [[sodium cyclopentadienide]]. [[Sodium tetraphenylborate]] can also be classified as an organosodium compound since in the solid state sodium is bound to the aryl groups. Organometallic compounds of the higher alkali metals are even more reactive than organosodium compounds and of limited utility. A notable reagent is [[Schlosser's base]], a mixture of [[n-Butyllithium|''n''-butyllithium]] and [[potassium tert-butoxide|potassium ''tert''-butoxide]]. This reagent reacts with [[propene]] to form the compound [[allylpotassium]] (KCHCHCH). [[cis-2-butene|''cis''-2-Butene]] and [[trans-2-butene|''trans''-2-butene]] equilibrate when in contact with alkali metals. Whereas [[isomerisation]] is fast with lithium and sodium, it is slow with the heavier alkali metals. The heavier alkali metals also favour the [[steric hindrance|sterically]] congested conformation. Several crystal structures of organopotassium compounds have been reported, establishing that they, like the sodium compounds, are polymeric. Organosodium, organopotassium, organorubidium and organocaesium compounds are all mostly ionic and are insoluble (or nearly so) in nonpolar solvents. Alkyl and aryl derivatives of sodium and potassium tend to react with air. They cause the cleavage of [[ether]], generating alkoxides. Unlike alkyllithium compounds, alkylsodiums and alkylpotassiums cannot be made by reacting the metals with alkyl halides because [[Wurtz coupling]] occurs: RM + R'X → R–R' + MX As such, they have to be made by reacting [[organomercury compound|alkylmercury]] compounds with sodium or potassium metal in inert hydrocarbon solvents. While methylsodium forms tetramers like methyllithium, methylpotassium is more ionic and has the [[nickel arsenide]] structure with discrete methyl anions and potassium cations. The alkali metals and their hydrides react with acidic hydrocarbons, for example [[cyclopentadiene]] and terminal alkynes, to give salts. Liquid ammonia, ether, or hydrocarbon solvents are used, the most common of which being [[tetrahydrofuran]]. The most important of these compounds is [[sodium cyclopentadienide]], NaCH, an important precursor to many transition metal cyclopentadienyl derivatives. Similarly, the alkali metals react with [[cyclooctatetraene]] in tetrahydrofuran to give alkali metal [[cyclooctatetraenide]]; for example, [[dipotassium cyclooctatetraenide]] (KCH) is an important precursor to many metal cyclooctatetraenyl derivatives, such as [[uranocene]]. The large and very weakly polarising alkali metal cations can stabilise large, aromatic, polarisable radical anions, such as the dark-green [[sodium naphthalenide]], Na[CH•], a strong reducing agent. | 666 | Alkali metal | [
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"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
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[
"Representative reactions of alkali metals"
]
| '''''Reaction with oxygen''''' Upon reacting with oxygen, alkali metals form [[oxides]], [[peroxides]], [[superoxides]] and [[suboxides]]. However, the first three are more common. The table below shows the types of compounds formed in reaction with oxygen. The compound in brackets represents the minor product of combustion. The alkali metal peroxides are ionic compounds that are unstable in water. The peroxide anion is weakly bound to the cation, and it is hydrolysed, forming stronger covalent bonds. NaO + 2HO → 2NaOH + HO The other oxygen compounds are also unstable in water. 2KO + 2HO → 2KOH + HO + O LiO + HO → 2LiOH '''''Reaction with sulphur''''' With sulphur, they form sulphides and polysulphides. 2Na + 1/8S → NaS + 1/8S → NaS...NaS Because alkali metal sulphides are essentially salts of a weak acid and a strong base, they form basic solutions. S + HO → HS + HO HS + HO → HS + HO '''''Reaction with nitrogen''''' Lithium is the only metal that combines directly with nitrogen at room temperature. 3Li + 1/3N → LiN LiN can react with water to liberate ammonia. LiN + 3HO → 3LiOH + NH '''''Reaction with hydrogen''''' With hydrogen, alkali metals form saline hydrides that hydrolyse in water. Na + H → NaH (at high temperatures) NaH + HO → NaOH + H '''''Reaction with carbon''''' Lithium is the only metal that reacts directly with carbon to give dilithium acetylide. Na and K can react with [[acetylene]] to give acetylides. 2Li + 2C → LiC Na + CH → NaCH + 1/2H (at 150C) Na + NaCH → NaC (at 220C) '''''Reaction with water''''' On reaction with water, they generate hydroxide ions and [[hydrogen]] gas. This reaction is vigorous and highly exothermic and the hydrogen resulted may ignite in air or even explode in the case of Rb and Cs. Na + HO → NaOH + 1/2H '''''Reaction with other salts''''' The alkali metals are very good reducing agents. They can reduce metal cations that are less electropositive. [[Titanium]] is produced industrially by the reduction of titanium tetrachloride with Na at 400C ([[van Arkel process]]). TiCl + 4Na → 4NaCl + Ti '''''Reaction with organohalide compounds''''' Alkali metals react with halogen derivatives to generate hydrocarbon via the [[Wurtz reaction]]. 2CH-Cl + 2Na → HC-CH + 2NaCl '''''Alkali metals in liquid ammonia''''' Alkali metals dissolve in liquid ammonia or other donor solvents like aliphatic amines or hexamethylphosphoramide to give blue solutions. These solutions are believed to contain free electrons. Na + xNH → Na + e(NH) Due to the presence of [[solvated electrons]], these solutions are very powerful reducing agents used in organic synthesis. Reaction 1) is known as [[Birch reduction]]. Other reductions that can be carried by these solutions are: S + 2e → S Fe(CO) + 2e → Fe(CO) + CO | 666 | Alkali metal | [
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"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
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[
"Extensions"
]
| Although francium is the heaviest alkali metal that has been discovered, there has been some theoretical work predicting the physical and chemical characteristics of hypothetical heavier alkali metals. Being the first [[period 8 element]], the undiscovered element [[ununennium]] (element 119) is predicted to be the next alkali metal after francium and behave much like their lighter [[Congener (chemistry)|congeners]]; however, it is also predicted to differ from the lighter alkali metals in some properties. Its chemistry is predicted to be closer to that of potassium or rubidium instead of caesium or francium. This is unusual as [[periodic trends]], ignoring relativistic effects would predict ununennium to be even more reactive than caesium and francium. This lowered [[reactivity (chemistry)|reactivity]] is due to the relativistic stabilisation of ununennium's valence electron, increasing ununennium's first ionisation energy and decreasing the [[metallic radius|metallic]] and [[ionic radius|ionic radii]]; this effect is already seen for francium. This assumes that ununennium will behave chemically as an alkali metal, which, although likely, may not be true due to relativistic effects. The relativistic stabilisation of the 8s orbital also increases ununennium's [[electron affinity]] far beyond that of caesium and francium; indeed, ununennium is expected to have an electron affinity higher than all the alkali metals lighter than it. Relativistic effects also cause a very large drop in the [[polarisability]] of ununennium. On the other hand, ununennium is predicted to continue the trend of melting points decreasing going down the group, being expected to have a melting point between 0 °C and 30 °C. The stabilisation of ununennium's valence electron and thus the contraction of the 8s orbital cause its atomic radius to be lowered to 240 [[picometer|pm]], very close to that of rubidium (247 pm), so that the chemistry of ununennium in the +1 oxidation state should be more similar to the chemistry of rubidium than to that of francium. On the other hand, the ionic radius of the Uue ion is predicted to be larger than that of Rb, because the 7p orbitals are destabilised and are thus larger than the p-orbitals of the lower shells. Ununennium may also show the +3 [[oxidation state]], which is not seen in any other alkali metal, in addition to the +1 oxidation state that is characteristic of the other alkali metals and is also the main oxidation state of all the known alkali metals: this is because of the destabilisation and expansion of the 7p spinor, causing its outermost electrons to have a lower ionisation energy than what would otherwise be expected. Indeed, many ununennium compounds are expected to have a large [[covalent]] character, due to the involvement of the 7p electrons in the bonding. | 666 | Alkali metal | [
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"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
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[
"Extensions"
]
| Not as much work has been done predicting the properties of the alkali metals beyond ununennium. Although a simple extrapolation of the periodic table (by the [[aufbau principle]]) would put element 169, unhexennium, under ununennium, Dirac-Fock calculations predict that the next element after ununennium with alkali-metal-like properties may be element 165, unhexpentium, which is predicted to have the electron configuration [Og] 5g 6f 7d 8s 8p 9s. This element would be intermediate in properties between an alkali metal and a [[group 11 element]], and while its physical and atomic properties would be closer to the former, its chemistry may be closer to that of the latter. Further calculations show that unhexpentium would follow the trend of increasing ionisation energy beyond caesium, having an ionisation energy comparable to that of sodium, and that it should also continue the trend of decreasing atomic radii beyond caesium, having an atomic radius comparable to that of potassium. However, the 7d electrons of unhexpentium may also be able to participate in chemical reactions along with the 9s electron, possibly allowing oxidation states beyond +1, whence the likely transition metal behaviour of unhexpentium. Due to the alkali and [[alkaline earth metal]] both being [[s-block]] elements, these predictions for the trends and properties of ununennium and unhexpentium also mostly hold quite similarly for the corresponding alkaline earth metals [[unbinilium]] (Ubn) and unhexhexium (Uhh). Unsepttrium, element 173, may be an even better heavier homologue of ununennium; with a predicted electron configuration of [Usb] 6g, it returns to the alkali-metal-like situation of having one easily removed electron far above a closed p-shell in energy, and is expected to be even more reactive than caesium. The probable properties of further alkali metals beyond unsepttrium have not been explored yet as of 2019, and they may or may not be able to exist. In periods 8 and above of the periodic table, relativistic and shell-structure effects become so strong that extrapolations from lighter congeners become completely inaccurate. In addition, the relativistic and shell-structure effects (which stabilise the s-orbitals and destabilise and expand the d-, f-, and g-orbitals of higher shells) have opposite effects, causing even larger difference between relativistic and non-relativistic calculations of the properties of elements with such high atomic numbers. Interest in the chemical properties of ununennium, unhexpentium, and unsepttrium stems from the fact that they are located close to the expected locations of [[island of stability|islands of stability]], centered at elements 122 (Ubb) and 164 (Uhq). | 666 | Alkali metal | [
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"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
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[
"Pseudo-alkali metals"
]
| Many other substances are similar to the alkali metals in their tendency to form monopositive cations. Analogously to the [[pseudohalogen]], they have sometimes been called "pseudo-alkali metals". These substances include some elements and many more [[polyatomic ion]]; the polyatomic ions are especially similar to the alkali metals in their large size and weak polarising power. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Pseudo-alkali metals",
"Hydrogen"
]
| The element [[hydrogen]], with one electron per neutral atom, is usually placed at the top of Group 1 of the periodic table for convenience, but hydrogen is not normally considered to be an alkali metal; when it is considered to be an alkali metal, it is because of its atomic properties and not its chemical properties. Under typical conditions, pure hydrogen exists as a [[diatomic]] gas consisting of two atoms per [[molecule]] (H); however, the alkali metals only form diatomic molecules (such as [[dilithium]], Li) at high temperatures, when they are in the [[gas]] state. Hydrogen, like the alkali metals, has one [[valence electron]] and reacts easily with the [[halogen]], but the similarities mostly end there because of the small size of a bare proton H compared to the alkali metal cations. Its placement above lithium is primarily due to its [[electron configuration]]. It is sometimes placed above [[fluorine]] due to their similar chemical properties, though the resemblance is likewise not absolute. The first ionisation energy of hydrogen (1312.0 [[kilojoule per mole|kJ/mol]]) is much higher than that of the alkali metals. As only one additional electron is required to fill in the outermost shell of the hydrogen atom, hydrogen often behaves like a halogen, forming the negative [[hydride]] ion, and is very occasionally considered to be a halogen on that basis. (The alkali metals can also form negative ions, known as [[alkalide]], but these are little more than laboratory curiosities, being unstable.) An argument against this placement is that formation of hydride from hydrogen is endothermic, unlike the exothermic formation of halides from halogens. The radius of the H anion also does not fit the trend of increasing size going down the halogens: indeed, H is very diffuse because its single proton cannot easily control both electrons. It was expected for some time that liquid hydrogen would show metallic properties; while this has been shown to not be the case, under extremely high [[pressure]], such as those found at the cores of [[Jupiter]] and [[Saturn]], hydrogen does become metallic and behaves like an alkali metal; in this phase, it is known as [[metallic hydrogen]]. The [[resistivity|electrical resistivity]] of liquid [[metallic hydrogen]] at 3000 K is approximately equal to that of liquid [[rubidium]] and [[caesium]] at 2000 K at the respective pressures when they undergo a nonmetal-to-metal transition. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Pseudo-alkali metals",
"Hydrogen"
]
| The 1s electron configuration of hydrogen, while analogous to that of the alkali metals (ns), is unique because there is no 1p subshell. Hence it can lose an electron to form the [[hydron (chemistry)|hydron]] H, or gain one to form the [[hydride]] ion H. In the former case it resembles superficially the alkali metals; in the latter case, the halogens, but the differences due to the lack of a 1p subshell are important enough that neither group fits the properties of hydrogen well. Group 14 is also a good fit in terms of thermodynamic properties such as [[ionisation energy]] and [[electron affinity]], but hydrogen cannot be tetravalent. Thus none of the three placements are entirely satisfactory, although group 1 is the most common placement (if one is chosen) because the hydron is by far the most important of all monatomic hydrogen species, being the foundation of acid-base chemistry. As an example of hydrogen's unorthodox properties stemming from its unusual electron configuration and small size, the hydrogen ion is very small (radius around 150 [[femtometre|fm]] compared to the 50–220 pm size of most other atoms and ions) and so is nonexistent in condensed systems other than in association with other atoms or molecules. Indeed, transferring of protons between chemicals is the basis of [[acid-base chemistry]]. Also unique is hydrogen's ability to form [[hydrogen bond]], which are an effect of charge-transfer, [[electrostatic]], and electron correlative contributing phenomena. While analogous lithium bonds are also known, they are mostly electrostatic. Nevertheless, hydrogen can take on the same structural role as the alkali metals in some molecular crystals, and has a close relationship with the lightest alkali metals (especially lithium). | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Pseudo-alkali metals",
"Ammonium and derivatives"
]
| The [[ammonium]] ion () has very similar properties to the heavier alkali metals, acting as an alkali metal intermediate between potassium and rubidium, and is often considered a close relative. For example, most alkali metal [[salt (chemistry)|salts]] are [[solubility|soluble]] in water, a property which ammonium salts share. Ammonium is expected to behave stably as a metal ( ions in a sea of delocalised electrons) at very high pressures (though less than the typical pressure where transitions from insulating to metallic behaviour occur around, 100 [[pascal (unit)|GPa]]), and could possibly occur inside the [[Gas giant#Uranus and Neptune|ice giants]] [[Uranus]] and [[Neptune]], which may have significant impacts on their interior magnetic fields. It has been estimated that the transition from a mixture of [[ammonia]] and dihydrogen molecules to metallic ammonium may occur at pressures just below 25 GPa. Under standard conditions, ammonium can form a metallic amalgam with mercury. Other "pseudo-alkali metals" include the [[alkylammonium]] cations, in which some of the hydrogen atoms in the ammonium cation are replaced by alkyl or aryl groups. In particular, the [[quaternary ammonium cation]] () are very useful since they are permanently charged, and they are often used as an alternative to the expensive Cs to stabilise very large and very easily polarisable anions such as . Tetraalkylammonium hydroxides, like alkali metal hydroxides, are very strong bases that react with atmospheric carbon dioxide to form carbonates. Furthermore, the nitrogen atom may be replaced by a phosphorus, arsenic, or antimony atom (the heavier nonmetallic [[pnictogen]]), creating a [[phosphonium]] () or [[arsonium]] () cation that can itself be substituted similarly; while [[stibonium]] () itself is not known, some of its organic derivatives are characterised. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Pseudo-alkali metals",
"Cobaltocene and derivatives"
]
| [[Cobaltocene]], Co(CH), is a [[metallocene]], the [[cobalt]] analogue of [[ferrocene]]. It is a dark purple solid. Cobaltocene has 19 valence electrons, one more than usually found in organotransition metal complexes, such as its very stable relative, ferrocene, in accordance with the [[18-electron rule]]. This additional electron occupies an orbital that is antibonding with respect to the Co–C bonds. Consequently, many chemical reactions of Co(CH) are characterized by its tendency to lose this "extra" electron, yielding a very stable 18-electron cation known as cobaltocenium. Many cobaltocenium salts coprecipitate with caesium salts, and cobaltocenium hydroxide is a strong base that absorbs atmospheric carbon dioxide to form cobaltocenium carbonate. Like the alkali metals, cobaltocene is a strong reducing agent, and [[decamethylcobaltocene]] is stronger still due to the combined [[inductive effect]] of the ten methyl groups. Cobalt may be substituted by its heavier congener [[rhodium]] to give [[rhodocene]], an even stronger reducing agent. [[Iridocene]] (involving [[iridium]]) would presumably be still more potent, but is not very well-studied due to its instability. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Pseudo-alkali metals",
"Thallium"
]
| [[Thallium]] is the heaviest stable element in group 13 of the periodic table. At the bottom of the periodic table, the [[inert pair effect]] is quite strong, because of the [[relativistic effects|relativistic]] stabilisation of the 6s orbital and the decreasing bond energy as the atoms increase in size so that the amount of energy released in forming two more bonds is not worth the high ionisation energies of the 6s electrons. It displays the +1 [[oxidation state]] that all the known alkali metals display, and thallium compounds with thallium in its +1 [[oxidation state]] closely resemble the corresponding potassium or [[silver]] compounds stoichiometrically due to the similar ionic radii of the Tl (164 [[picometer|pm]]), K (152 pm) and Ag (129 pm) ions. It was sometimes considered an alkali metal in [[continental Europe]] (but not in England) in the years immediately following its discovery, and was placed just after caesium as the sixth alkali metal in [[Dmitri Mendeleev]]'s 1869 [[periodic table]] and [[Julius Lothar Meyer]]'s 1868 periodic table. (Mendeleev's 1871 periodic table and Meyer's 1870 periodic table put thallium in its current position in the [[boron group]] and left the space below caesium blank.) However, thallium also displays the oxidation state +3, which no known alkali metal displays (although ununennium, the undiscovered seventh alkali metal, is predicted to possibly display the +3 oxidation state). The sixth alkali metal is now considered to be francium. While Tl is stabilised by the inert pair effect, this inert pair of 6s electrons is still able to participate chemically, so that these electrons are [[stereochemistry|stereochemically]] active in aqueous solution. Additionally, the thallium halides (except [[thallium(I) fluoride|TlF]]) are quite insoluble in water, and [[thallium(I) iodide|TlI]] has an unusual structure because of the presence of the stereochemically active inert pair in thallium. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Pseudo-alkali metals",
"Copper, silver, and gold"
]
| The [[group 11 element|group 11 metals]] (or coinage metals), [[copper]], [[silver]], and [[gold]], are typically categorised as transition metals given they can form ions with incomplete d-shells. Physically, they have the relatively low melting points and high electronegativity values associated with [[post-transition metal]]. "The filled ''d'' subshell and free ''s'' electron of Cu, Ag, and Au contribute to their high electrical and thermal conductivity. Transition metals to the left of group 11 experience interactions between ''s'' electrons and the partially filled ''d'' subshell that lower electron mobility." Chemically, the group 11 metals behave like main-group metals in their +1 valence states, and are hence somewhat related to the alkali metals: this is one reason for their previously being labelled as "group IB", paralleling the alkali metals' "group IA". They are occasionally classified as post-transition metals. Their spectra are analogous to those of the alkali metals. Their monopositive ions are [[paramagnetic]] and contribute no colour to their salts, like those of the alkali metals. In Mendeleev's 1871 periodic table, copper, silver, and gold are listed twice, once under group VIII (with the [[iron triad]] and [[platinum group metal]]), and once under group IB. Group IB was nonetheless parenthesised to note that it was tentative. Mendeleev's main criterion for group assignment was the maximum oxidation state of an element: on that basis, the group 11 elements could not be classified in group IB, due to the existence of copper(II) and gold(III) compounds being known at that time. However, eliminating group IB would make group I the only main group (group VIII was labelled a transition group) to lack an A–B bifurcation. Soon afterward, a majority of chemists chose to classify these elements in group IB and remove them from group VIII for the resulting symmetry: this was the predominant classification until the rise of the modern medium-long 18-column periodic table, which separated the alkali metals and group 11 metals. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Pseudo-alkali metals",
"Copper, silver, and gold"
]
| The coinage metals were traditionally regarded as a subdivision of the alkali metal group, due to them sharing the characteristic s electron configuration of the alkali metals (group 1: ps; group 11: ds). However, the similarities are largely confined to the [[stochiometry|stoichiometries]] of the +1 compounds of both groups, and not their chemical properties. This stems from the filled d subshell providing a much weaker shielding effect on the outermost s electron than the filled p subshell, so that the coinage metals have much higher first ionisation energies and smaller ionic radii than do the corresponding alkali metals. Furthermore, they have higher melting points, hardnesses, and densities, and lower reactivities and solubilities in liquid [[ammonia]], as well as having more covalent character in their compounds. Finally, the alkali metals are at the top of the [[electrochemical series]], whereas the coinage metals are almost at the very bottom. The coinage metals' filled d shell is much more easily disrupted than the alkali metals' filled p shell, so that the second and third ionisation energies are lower, enabling higher oxidation states than +1 and a richer coordination chemistry, thus giving the group 11 metals clear [[transition metal]] character. Particularly noteworthy is gold forming ionic compounds with rubidium and caesium, in which it forms the auride ion (Au) which also occurs in solvated form in liquid ammonia solution: here gold behaves as a [[pseudohalogen]] because its 5d6s configuration has one electron less than the quasi-closed shell 5d6s configuration of [[mercury (element)|mercury]]. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Production and isolation"
]
| The production of pure alkali metals is somewhat complicated due to their extreme reactivity with commonly used substances, such as water. From their [[silicate]] ores, all the stable alkali metals may be obtained the same way: [[sulfuric acid]] is first used to dissolve the desired alkali metal ion and [[aluminium]](III) ions from the ore (leaching), whereupon basic precipitation removes aluminium ions from the mixture by precipitating it as the [[aluminium hydroxide|hydroxide]]. The remaining insoluble alkali metal [[carbonate]] is then precipitated selectively; the salt is then dissolved in [[hydrochloric acid]] to produce the chloride. The result is then left to evaporate and the alkali metal can then be isolated. Lithium and sodium are typically isolated through electrolysis from their liquid chlorides, with [[calcium chloride]] typically added to lower the melting point of the mixture. The heavier alkali metals, however, is more typically isolated in a different way, where a reducing agent (typically sodium for potassium and [[magnesium]] or [[calcium]] for the heaviest alkali metals) is used to reduce the alkali metal chloride. The liquid or gaseous product (the alkali metal) then undergoes [[fractional distillation]] for purification. Most routes to the pure alkali metals require the use of electrolysis due to their high reactivity; one of the few which does not is the [[pyrolysis]] of the corresponding alkali metal [[azide]], which yields the metal for sodium, potassium, rubidium, and caesium and the nitride for lithium. Lithium salts have to be extracted from the water of [[mineral spring]], [[brine]] pools, and brine deposits. The metal is produced electrolytically from a mixture of fused [[lithium chloride]] and [[potassium chloride]]. Sodium occurs mostly in seawater and dried [[seabed]], but is now produced through [[electrolysis]] of [[sodium chloride]] by lowering the melting point of the substance to below 700 °C through the use of a [[Downs cell]]. Extremely pure sodium can be produced through the thermal decomposition of [[sodium azide]]. Potassium occurs in many minerals, such as [[sylvite]] ([[potassium chloride]]). Previously, potassium was generally made from the electrolysis of [[potassium chloride]] or [[potassium hydroxide]], found extensively in places such as Canada, Russia, Belarus, Germany, Israel, United States, and Jordan, in a method similar to how sodium was produced in the late 1800s and early 1900s. It can also be produced from [[seawater]]. However, these methods are problematic because the potassium metal tends to dissolve in its molten chloride and vaporises significantly at the operating temperatures, potentially forming the explosive superoxide. As a result, pure potassium metal is now produced by reducing molten potassium chloride with sodium metal at 850 °C. Na (g) + KCl (l) NaCl (l) + K (g) Although sodium is less reactive than potassium, this process works because at such high temperatures potassium is more volatile than sodium and can easily be distilled off, so that the equilibrium shifts towards the right to produce more potassium gas and proceeds almost to completion. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Production and isolation"
]
| For several years in the 1950s and 1960s, a by-product of the potassium production called Alkarb was a main source for rubidium. Alkarb contained 21% rubidium while the rest was potassium and a small fraction of caesium. Today the largest producers of caesium, for example the [[Tanco Mine]] in Manitoba, Canada, produce rubidium as by-product from [[pollucite]]. Today, a common method for separating rubidium from potassium and caesium is the [[fractional crystallization (chemistry)|fractional crystallisation]] of a rubidium and caesium [[alum]] ([[Caesium|Cs]], [[Rubidium|Rb]])[[Aluminium|Al]]([[Sulfate|SO]])·12[[Water|HO]], which yields pure rubidium alum after approximately 30 recrystallisations. The limited applications and the lack of a mineral rich in rubidium limit the production of rubidium compounds to 2 to 4 [[tonne]] per year. Caesium, however, is not produced from the above reaction. Instead, the mining of [[pollucite]] ore is the main method of obtaining pure caesium, extracted from the ore mainly by three methods: acid digestion, alkaline decomposition, and direct reduction. Both metals are produced as by-products of lithium production: after 1958, when interest in lithium's thermonuclear properties increased sharply, the production of rubidium and caesium also increased correspondingly. Pure rubidium and caesium metals are produced by reducing their chlorides with [[calcium]] metal at 750 °C and low pressure. As a result of its extreme rarity in nature, most francium is synthesised in the nuclear reaction [[Gold|Au]] + [[Oxygen|O]] → [[Francium|Fr]] + 5 [[neutron|n]], yielding [[francium-209]], [[francium-210]], and [[francium-211]]. The greatest quantity of francium ever assembled to date is about 300,000 neutral atoms, which were synthesised using the nuclear reaction given above. When the only natural isotope francium-223 is specifically required, it is produced as the alpha daughter of actinium-227, itself produced synthetically from the neutron irradiation of natural radium-226, one of the daughters of natural uranium-238. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Applications"
]
| Lithium, sodium, and potassium have many applications, while rubidium and caesium are very useful in academic contexts but do not have many applications yet. Lithium is often used in [[lithium-ion battery|lithium-ion batteries]], and [[lithium oxide]] can help process silica. [[Lithium stearate]] is a thickener and can be used to make lubricating greases; it is produced from lithium hydroxide, which is also used to absorb [[carbon dioxide]] in space capsules and submarines. [[Lithium chloride]] is used as a brazing alloy for aluminium parts. Metallic lithium is used in alloys with magnesium and aluminium to give very tough and light alloys. Sodium compounds have many applications, the most well-known being sodium chloride as [[table salt]]. Sodium salts of [[fatty acid]] are used as soap. Pure sodium metal also has many applications, including use in [[sodium-vapor lamp|sodium-vapour lamps]], which produce very efficient light compared to other types of lighting, and can help smooth the surface of other metals. Being a strong reducing agent, it is often used to reduce many other metals, such as [[titanium]] and [[zirconium]], from their chlorides. Furthermore, it is very useful as a heat-exchange liquid in [[fast breeder nuclear reactor]] due to its low melting point, viscosity, and [[cross-section (physics)|cross-section]] towards neutron absorption. Potassium compounds are often used as [[fertiliser]] as potassium is an important element for plant nutrition. [[Potassium hydroxide]] is a very strong base, and is used to control the [[pH]] of various substances. [[Potassium nitrate]] and [[potassium permanganate]] are often used as powerful oxidising agents. [[Potassium superoxide]] is used in breathing masks, as it reacts with carbon dioxide to give potassium carbonate and oxygen gas. Pure potassium metal is not often used, but its alloys with sodium may substitute for pure sodium in fast breeder nuclear reactors. Rubidium and caesium are often used in [[atomic clock]]. Caesium atomic clocks are extraordinarily accurate; if a clock had been made at the time of the dinosaurs, it would be off by less than four seconds (after 80 million years). For that reason, caesium atoms are used as the definition of the second. Rubidium ions are often used in purple [[firework]], and caesium is often used in drilling fluids in the petroleum industry. Francium has no commercial applications, but because of francium's relatively simple [[atomic structure]], among other things, it has been used in [[spectroscopy]] experiments, leading to more information regarding [[energy level]] and the [[coupling constant]] between [[subatomic particle]]. Studies on the light emitted by laser-trapped francium-210 ions have provided accurate data on transitions between atomic energy levels, similar to those predicted by [[quantum mechanics|quantum theory]]. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Biological role and precautions",
"Metals"
]
| Pure alkali metals are dangerously reactive with air and water and must be kept away from heat, fire, oxidising agents, acids, most organic compounds, [[halocarbon]], [[plastic]], and moisture. They also react with carbon dioxide and carbon tetrachloride, so that normal fire extinguishers are counterproductive when used on alkali metal fires. Some Class D dry powder [[fire extinguisher|extinguishers]] designed for metal fires are effective, depriving the fire of oxygen and cooling the alkali metal. Experiments are usually conducted using only small quantities of a few grams in a [[fume hood]]. Small quantities of lithium may be disposed of by reaction with cool water, but the heavier alkali metals should be dissolved in the less reactive [[isopropanol]]. The alkali metals must be stored under [[mineral oil]] or an inert atmosphere. The inert atmosphere used may be [[argon]] or nitrogen gas, except for lithium, which reacts with nitrogen. Rubidium and caesium must be kept away from air, even under oil, because even a small amount of air diffused into the oil may trigger formation of the dangerously explosive peroxide; for the same reason, potassium should not be stored under oil in an oxygen-containing atmosphere for longer than 6 months. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Biological role and precautions",
"Ions"
]
| The bioinorganic chemistry of the alkali metal ions has been extensively reviewed. Solid state crystal structures have been determined for many complexes of alkali metal ions in small peptides, nucleic acid constituents, carbohydrates and ionophore complexes. Lithium naturally only occurs in traces in biological systems and has no known biological role, but does have effects on the body when ingested. [[Lithium carbonate]] is used as a [[mood stabiliser]] in [[psychiatry]] to treat [[bipolar disorder]] ([[manic-depression]]) in daily doses of about 0.5 to 2 grams, although there are side-effects. Excessive ingestion of lithium causes drowsiness, slurred speech and vomiting, among other symptoms, and [[poison]] the [[central nervous system]], which is dangerous as the required dosage of lithium to treat bipolar disorder is only slightly lower than the toxic dosage. Its biochemistry, the way it is handled by the human body and studies using rats and goats suggest that it is an [[essential element|essential]] [[trace element]], although the natural biological function of lithium in humans has yet to be identified. Sodium and potassium occur in all known biological systems, generally functioning as [[electrolytes]] inside and outside [[cell (biology)|cells]]. Sodium is an essential nutrient that regulates blood volume, blood pressure, osmotic equilibrium and [[pH]]; the minimum physiological requirement for sodium is 500 milligrams per day. [[Sodium chloride]] (also known as common salt) is the principal source of sodium in the diet, and is used as seasoning and preservative, such as for [[pickling]] and [[jerky (food)|jerky]]; most of it comes from processed foods. The [[Dietary Reference Intake]] for sodium is 1.5 grams per day, but most people in the United States consume more than 2.3 grams per day, the minimum amount that promotes hypertension; this in turn causes 7.6 million premature deaths worldwide. Potassium is the major [[cation]] (positive ion) inside [[cell (biology)|animal cells]], while sodium is the major cation outside animal cells. The [[concentration]] differences of these charged particles causes a difference in [[electric potential]] between the inside and outside of cells, known as the [[membrane potential]]. The balance between potassium and sodium is maintained by [[ion transporter]] proteins in the [[cell membrane]]. The cell membrane potential created by potassium and sodium ions allows the cell to generate an [[action potential]]—a "spike" of electrical discharge. The ability of cells to produce electrical discharge is critical for body functions such as [[neurotransmission]], muscle contraction, and heart function. Disruption of this balance may thus be fatal: for example, ingestion of large amounts of potassium compounds can lead to [[hyperkalemia]] strongly influencing the cardiovascular system. Potassium chloride is used in the [[United States]] for [[lethal injection]] executions. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[
"Biological role and precautions",
"Ions"
]
| Due to their similar atomic radii, rubidium and caesium in the body mimic potassium and are taken up similarly. Rubidium has no known biological role, but may help stimulate [[metabolism]], and, similarly to caesium, replace potassium in the body causing [[hypokalemia|potassium deficiency]]. Partial substitution is quite possible and rather non-toxic: a 70 kg person contains on average 0.36 g of rubidium, and an increase in this value by 50 to 100 times did not show negative effects in test persons. Rats can survive up to 50% substitution of potassium by rubidium. Rubidium (and to a much lesser extent caesium) can function as temporary cures for hypokalemia; while rubidium can adequately physiologically substitute potassium in some systems, caesium is never able to do so. There is only very limited evidence in the form of deficiency symptoms for rubidium being possibly essential in goats; even if this is true, the trace amounts usually present in food are more than enough. Caesium compounds are rarely encountered by most people, but most caesium compounds are mildly toxic. Like rubidium, caesium tends to substitute potassium in the body, but is significantly larger and is therefore a poorer substitute. Excess caesium can lead to [[hypokalemia]], [[arrythmia]], and acute [[cardiac arrest]], but such amounts would not ordinarily be encountered in natural sources. As such, caesium is not a major chemical environmental pollutant. The [[median lethal dose]] (LD) value for [[caesium chloride]] in mice is 2.3 g per kilogram, which is comparable to the LD values of [[potassium chloride]] and [[sodium chloride]]. Caesium chloride has been promoted as an alternative cancer therapy, but has been linked to the deaths of over 50 patients, on whom it was used as part of a scientifically unvalidated cancer treatment. [[Radioisotope]] of caesium require special precautions: the improper handling of caesium-137 [[gamma ray]] sources can lead to release of this radioisotope and radiation injuries. Perhaps the best-known case is the Goiânia accident of 1987, in which an improperly-disposed-of radiation therapy system from an abandoned clinic in the city of [[Goiânia]], [[Brazil]], was scavenged from a junkyard, and the glowing [[caesium chloride|caesium salt]] sold to curious, uneducated buyers. This led to four deaths and serious injuries from radiation exposure. Together with [[caesium-134]], [[iodine-131]], and [[strontium-90]], caesium-137 was among the isotopes distributed by the [[Chernobyl disaster]] which constitute the greatest risk to health. Radioisotopes of francium would presumably be dangerous as well due to their high decay energy and short half-life, but none have been produced in large enough amounts to pose any serious risk. | 666 | Alkali metal | [
"Chemical compounds by element",
"Alkali metals",
"Groups (periodic table)",
"Periodic table",
"Articles containing video clips"
]
| []
|
[]
| An '''alphabet''' is a standardized set of basic written [[symbols]] or [[graphemes]] (called [[letter (alphabet)|letters]]) that represent the [[phoneme]] of certain [[spoken language]]. Not all [[writing system]] represent language in this way; in a [[syllabary]], each character represents a [[syllable]], for instance, and [[Logogram|logographic systems]] use characters to represent words, [[morphemes]], or other semantic units. The first fully phonemic script, the [[Proto-Sinaitic script|Proto-Canaanite script]], later known as the [[Phoenician alphabet]], is considered to be the first alphabet, and is the ancestor of most modern alphabets, including [[Arabic alphabet|Arabic]], [[Cyrillic alphabet|Cyrillic]], [[Greek alphabet|Greek]], [[Hebrew alphabet|Hebrew]], [[Latin alphabet|Latin]], and possibly [[Brahmic scripts|Brahmic]]. It was created by Semitic-speaking workers and slaves in the [[Sinai Peninsula]] (as the [[Proto-Sinaitic script]]), by selecting a small number of [[Egyptian hieroglyphs|hieroglyphs]] commonly seen in their [[Ancient Egypt|Egyptian surroundings]] to [[Acrophony|describe the sounds]], as opposed to the semantic values, of their own [[Canaanite languages|Canaanite language]]. [[Peter T. Daniels]], however, distinguishes an [[abugida]] or alphasyllabary, a set of graphemes that represent consonantal base letters which [[diacritic]] modify to represent vowels (as in [[Devanagari]] and other South Asian scripts), an [[abjad]], in which letters predominantly or exclusively represent consonants (as in the original Phoenician, [[Hebrew alphabet|Hebrew]] or [[Arabic script|Arabic]]), and an "alphabet", a set of graphemes that represent both [[vowel]] and [[consonant]]. In this narrow sense of the word the first true alphabet was the [[Greek alphabet]], which was developed on the basis of the earlier [[Phoenician alphabet]]. Of the dozens of alphabets in use today, the most popular is the [[Latin alphabet]], which was derived from the [[Greek alphabet|Greek]], and which many [[language]] modify by adding letters formed using diacritical marks. While most alphabets have letters composed of lines ([[linear writing]]), there are also [[non-linear writing|exceptions]] such as the alphabets used in [[Braille]]. The [[Khmer alphabet]] (for [[Cambodian language|Cambodian]]) is the longest, with 74 letters. Alphabets are usually associated with a standard ordering of letters. This makes them useful for purposes of [[collation]], specifically by allowing words to be sorted in [[alphabetical order]]. It also means that their letters can be used as an alternative method of "numbering" ordered items, in such contexts as [[numbered list]] and number placements. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
"Alphabet effect",
"Constructed script",
"List of alphabets",
"Unicode",
"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[
"Etymology"
]
| The English word ''alphabet'' came into [[Middle English]] from the [[Late Latin]] word ''alphabetum'', which in turn originated in the [[Greek language|Greek]] ἀλφάβητος (''alphabētos''). The Greek word was made from the first two letters, ''[[alpha (letter)|alpha]]''(α) and ''[[beta (letter)|beta]]''(β). The names for the Greek letters came from the first two letters of the [[Phoenician alphabet]]; ''[[aleph]]'', which also meant ''ox'', and ''[[bet (letter)|bet]]'', which also meant ''house''. Sometimes, like in the [[alphabet song]] in English, the term "ABCs" is used instead of the word "alphabet" (''Now I know my ABCs''...). "Knowing one's ABCs", in general, can be used as a [[metaphor]] for knowing the basics about anything. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
"Alphabet effect",
"Constructed script",
"List of alphabets",
"Unicode",
"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[
"History",
"Ancient Northeast African and Middle Eastern scripts"
]
| The history of the alphabet started in [[ancient Egypt]]. Egyptian writing had a set of some [[Egyptian uniliteral signs|24 hieroglyphs]] that are called uniliterals, to represent syllables that begin with a single [[consonant]] of their language, plus a vowel (or no vowel) to be supplied by the native speaker. These glyphs were used as pronunciation guides for [[logogram]], to write grammatical inflections, and, later, to transcribe loan words and foreign names. In the [[Middle Bronze Age]], an apparently "alphabetic" system known as the [[Proto-Sinaitic script]] appears in Egyptian turquoise mines in the [[Sinai peninsula]] dated to circa the 15th century BC, apparently left by Canaanite workers. In 1999, John and Deborah Darnell discovered an even earlier version of this first alphabet at Wadi el-Hol dated to circa 1800 BC and showing evidence of having been adapted from specific forms of Egyptian hieroglyphs that could be dated to circa 2000 BC, strongly suggesting that the first alphabet had been developed about that time. Based on letter appearances and names, it is believed to be based on Egyptian hieroglyphs. This script had no characters representing vowels, although originally it probably was a syllabary, but unneeded symbols were discarded. An alphabetic [[cuneiform]] script with 30 signs including three that indicate the following vowel was invented in [[Ugarit]] before the 15th century BC. This script was not used after the destruction of Ugarit. The Proto-Sinaitic script eventually developed into the [[Phoenician alphabet]], which is conventionally called "Proto-Canaanite" before c. 1050 BC. The oldest text in Phoenician script is an inscription on the sarcophagus of King [[Ahiram]]. This script is the parent script of all western alphabets. By the tenth century, two other forms can be distinguished, namely [[Canaanite language|Canaanite]] and [[Aramaic alphabet|Aramaic]]. The Aramaic gave rise to the [[Hebrew alphabet|Hebrew]] script. The [[South Arabian alphabet]], a sister script to the Phoenician alphabet, is the script from which the [[Ge'ez alphabet]] (an [[abugida]]) is descended. Vowelless alphabets are called [[abjad]], currently exemplified in scripts including [[Arabic alphabet|Arabic]], [[Hebrew alphabet|Hebrew]], and [[Syriac alphabet|Syriac]]. The omission of vowels was not always a satisfactory solution and some "weak" consonants are sometimes used to indicate the vowel quality of a syllable ([[Mater lectionis|matres lectionis]]). These letters have a dual function since they are also used as pure consonants. The Proto-Sinaitic or Proto-Canaanite script and the [[Ugaritic script]] were the first scripts with a limited number of signs, in contrast to the other widely used writing systems at the time, [[Cuneiform]], [[Egyptian hieroglyphs]], and [[Linear B]]. The Phoenician script was probably the first phonemic script and it contained only about two dozen distinct letters, making it a script simple enough for common traders to learn. Another advantage of Phoenician was that it could be used to write down many different languages, since it recorded words phonemically. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
"Alphabet effect",
"Constructed script",
"List of alphabets",
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"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
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|
[
"History",
"Ancient Northeast African and Middle Eastern scripts"
]
| The script was spread by the Phoenicians across the Mediterranean. In Greece, the script was modified to add vowels, giving rise to the ancestor of all alphabets in the West. It was the first alphabet in which vowels have independent letter forms separate from those of consonants. The Greeks chose letters representing sounds that did not exist in Greek to represent vowels. Vowels are significant in the Greek language, and the syllabical [[Linear B]] script that was used by the [[Mycenaean Greece|Mycenaean]] Greeks from the 16th century BC had 87 symbols, including 5 vowels. In its early years, there were many variants of the Greek alphabet, a situation that caused many different alphabets to evolve from it. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
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"Constructed script",
"List of alphabets",
"Unicode",
"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[
"History",
"European alphabets"
]
| The [[Greek alphabet]], in its [[Euboean alphabet|Euboean form]], was carried over by Greek colonists to the Italian peninsula, where it gave rise to a variety of alphabets used to write the [[Italic languages]]. One of these became the [[Latin alphabet]], which was spread across Europe as the Romans expanded their empire. Even after the fall of the Roman state, the alphabet survived in intellectual and religious works. It eventually became used for the descendant languages of Latin (the [[Romance languages]]) and then for most of the other languages of Europe. Some adaptations of the Latin alphabet are augmented with [[ligature (typography)|ligatures]], such as [[æ]] in [[Danish language|Danish]] and [[Icelandic language|Icelandic]] and [[Ou (letter)|Ȣ]] in [[Algonquian languages|Algonquian]]; by borrowings from other alphabets, such as the [[thorn (letter)|thorn]] þ in [[Old English language|Old English]] and [[Icelandic language|Icelandic]], which came from the [[Runic alphabet|Futhark]] runes; and by modifying existing letters, such as the [[Eth (letter)|eth]] ð of Old English and Icelandic, which is a modified ''d''. Other alphabets only use a subset of the Latin alphabet, such as Hawaiian, and [[Italian language|Italian]], which uses the letters ''j, k, x, y'' and ''w'' only in foreign words. Another notable script is [[Elder Futhark]], which is believed to have evolved out of one of the [[Old Italic alphabet]]. Elder Futhark gave rise to a variety of alphabets known collectively as the [[Runic alphabet]]. The Runic alphabets were used for Germanic languages from AD 100 to the late Middle Ages. Its usage is mostly restricted to engravings on stone and jewelry, although inscriptions have also been found on bone and wood. These alphabets have since been replaced with the Latin alphabet, except for decorative usage for which the runes remained in use until the 20th century. The [[Old Hungarian script]] is a contemporary writing system of the Hungarians. It was in use during the entire history of Hungary, albeit not as an official writing system. From the 19th century it once again became more and more popular. The [[Glagolitic alphabet]] was the initial script of the liturgical language [[Old Church Slavonic]] and became, together with the Greek uncial script, the basis of the [[Cyrillic script]]. Cyrillic is one of the most widely used modern alphabetic scripts, and is notable for its use in Slavic languages and also for other languages within the former [[Soviet Union]]. [[Cyrillic alphabets]] include the [[Serbian Cyrillic alphabet|Serbian]], [[Macedonian alphabet|Macedonian]], [[Bulgarian alphabet|Bulgarian]], [[Russian alphabet|Russian]], [[Belarusian alphabet|Belarusian]] and [[Ukrainian alphabet|Ukrainian]]. The Glagolitic alphabet is believed to have been created by [[Saints Cyril and Methodius]], while the Cyrillic alphabet was invented by [[Clement of Ohrid]], who was their disciple. They feature many letters that appear to have been borrowed from or influenced by the [[Greek alphabet]] and the [[Hebrew alphabet]]. The longest European alphabet is the Latin-derived [[Slovak alphabet]] which has 46 letters. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
"Alphabet effect",
"Constructed script",
"List of alphabets",
"Unicode",
"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[
"History",
"Asian alphabets"
]
| Beyond the logographic [[Written Chinese|Chinese writing]], many phonetic scripts are in existence in Asia. The [[Arabic alphabet]], [[Hebrew alphabet]], [[Syriac alphabet]], and other [[abjad]] of the Middle East are developments of the [[Aramaic alphabet]]. Most alphabetic scripts of India and Eastern Asia are descended from the [[Brahmi script]], which is often believed to be a descendant of Aramaic. In [[Korea]], the [[Hangul]] alphabet was created by [[Sejong the Great]]. Hangul is a unique alphabet: it is a [[featural alphabet]], where many of the letters are designed from a sound's place of articulation (P to look like the widened mouth, L to look like the tongue pulled in, etc.); its design was planned by the government of the day; and it places individual letters in syllable clusters with equal dimensions, in the same way as [[Chinese characters]], to allow for mixed-script writing (one syllable always takes up one type-space no matter how many letters get stacked into building that one sound-block). [[Zhuyin]] (sometimes called ''Bopomofo'') is a [[semi-syllabary]] used to phonetically transcribe [[Standard Chinese|Mandarin Chinese]] in the [[Taiwan|Republic of China]]. After the later establishment of the [[China|People's Republic of China]] and its adoption of [[Pinyin|Hanyu Pinyin]], the use of Zhuyin today is limited, but it is still widely used in [[Taiwan]] where the Republic of China still governs. Zhuyin developed out of a form of Chinese shorthand based on Chinese characters in the early 1900s and has elements of both an alphabet and a syllabary. Like an alphabet the phonemes of [[syllable onset|syllable initials]] are represented by individual symbols, but like a syllabary the phonemes of the [[syllable rime|syllable finals]] are not; rather, each possible final (excluding the [[Syllable medial|medial glide]]) is represented by its own symbol. For example, ''luan'' is represented as ㄌㄨㄢ (''l-u-an''), where the last symbol ㄢ represents the entire final ''-an''. While Zhuyin is not used as a mainstream writing system, it is still often used in ways similar to a [[romanization]] system—that is, for aiding in pronunciation and as an input method for Chinese characters on computers and cellphones. European alphabets, especially Latin and Cyrillic, have been adapted for many languages of Asia. Arabic is also widely used, sometimes as an abjad (as with [[Urdu alphabet|Urdu]] and [[Persian alphabet|Persian]]) and sometimes as a complete alphabet (as with [[Kurdish alphabet|Kurdish]] and [[Uyghur alphabet|Uyghur]]). | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
"Alphabet effect",
"Constructed script",
"List of alphabets",
"Unicode",
"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[
"Types"
]
| The term "alphabet" is used by [[Linguistics|linguists]] and [[paleographer]] in both a wide and a narrow sense. In the wider sense, an alphabet is a script that is ''segmental'' at the [[phoneme]] level—that is, it has separate glyphs for individual sounds and not for larger units such as syllables or words. In the narrower sense, some scholars distinguish "true" alphabets from two other types of segmental script, [[abjad]] and [[abugida]]. These three differ from each other in the way they treat vowels: abjads have letters for consonants and leave most vowels unexpressed; abugidas are also consonant-based, but indicate vowels with [[diacritic]] to or a systematic graphic modification of the consonants. In alphabets in the narrow sense, on the other hand, consonants and vowels are written as independent letters. The earliest known alphabet in the wider sense is the [[Middle Bronze Age alphabets|Wadi el-Hol script]], believed to be an abjad, which through its successor [[Phoenician alphabet|Phoenician]] is the ancestor of modern alphabets, including [[Arabic alphabet|Arabic]], [[Greek alphabet|Greek]], [[Latin alphabet|Latin]] (via the [[Old Italic alphabet]]), [[Cyrillic]] (via the Greek alphabet) and [[Hebrew alphabet|Hebrew]] (via [[Aramaic alphabet|Aramaic]]). Examples of present-day abjads are the [[Arabic script|Arabic]] and [[Hebrew script]]; true alphabets include [[Latin script|Latin]], Cyrillic, and Korean [[hangul]]; and abugidas are used to write [[tigrinya language|Tigrinya]], [[Amharic language|Amharic]], [[Hindi]], and [[Thai language|Thai]]. The [[Canadian Aboriginal syllabics]] are also an abugida rather than a syllabary as their name would imply, since each glyph stands for a consonant that is modified by rotation to represent the following vowel. (In a true syllabary, each consonant-vowel combination would be represented by a separate glyph.) All three types may be augmented with syllabic glyphs. [[Ugaritic script|Ugaritic]], for example, is basically an abjad, but has syllabic letters for . (These are the only time vowels are indicated.) Cyrillic is basically a true alphabet, but has syllabic letters for (я, е, ю); [[Coptic alphabet|Coptic]] has a letter for . [[Devanagari]] is typically an abugida augmented with dedicated letters for initial vowels, though some traditions use अ as a [[zero consonant]] as the graphic base for such vowels. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
"Alphabet effect",
"Constructed script",
"List of alphabets",
"Unicode",
"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[
"Types"
]
| The boundaries between the three types of segmental scripts are not always clear-cut. For example, [[Sorani]] [[Kurdish language|Kurdish]] is written in the [[Arabic script]], which is normally an abjad. However, in Kurdish, writing the vowels is mandatory, and full letters are used, so the script is a true alphabet. Other languages may use a Semitic abjad with mandatory vowel diacritics, effectively making them abugidas. On the other hand, the [[Phagspa script]] of the [[Mongol Empire]] was based closely on the [[Tibetan script|Tibetan abugida]], but all vowel marks were written after the preceding consonant rather than as diacritic marks. Although short ''a'' was not written, as in the Indic abugidas, one could argue that the linear arrangement made this a true alphabet. Conversely, the vowel marks of the [[Ge'ez alphabet|Tigrinya abugida]] and the [[Ge'ez alphabet|Amharic abugida]] (ironically, the original source of the term "abugida") have been so completely assimilated into their consonants that the modifications are no longer systematic and have to be learned as a syllabary rather than as a segmental script. Even more extreme, the Pahlavi abjad eventually became [[logogram|logographic]]. (See below.) Thus the primary [[Categorisation|classification]] of alphabets reflects how they treat vowels. For [[Tone (linguistics)|tonal languages]], further classification can be based on their treatment of tone, though names do not yet exist to distinguish the various types. Some alphabets disregard tone entirely, especially when it does not carry a heavy functional load, as in [[Somali language|Somali]] and many other languages of Africa and the Americas. Such scripts are to tone what abjads are to vowels. Most commonly, tones are indicated with diacritics, the way vowels are treated in abugidas. This is the case for [[Vietnamese alphabet|Vietnamese]] (a true alphabet) and [[Thai alphabet|Thai]] (an abugida). In Thai, tone is determined primarily by the choice of consonant, with diacritics for disambiguation. In the [[Pollard script]], an abugida, vowels are indicated by diacritics, but the placement of the diacritic relative to the consonant is modified to indicate the tone. More rarely, a script may have separate letters for tones, as is the case for [[Hmong alphabet|Hmong]] and [[Zhuang alphabet|Zhuang]]. For most of these scripts, regardless of whether letters or diacritics are used, the most common tone is not marked, just as the most common vowel is not marked in Indic abugidas; in [[Zhuyin]] not only is one of the tones unmarked, but there is a diacritic to indicate lack of tone, like the [[virama]] of Indic. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
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"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[
"Types"
]
| The number of letters in an alphabet can be quite small. The Book [[Pahlavi scripts|Pahlavi]] script, an abjad, had only twelve letters at one point, and may have had even fewer later on. Today the [[Rotokas alphabet]] has only twelve letters. (The [[Hawaiian alphabet]] is sometimes claimed to be as small, but it actually consists of 18 letters, including the [[ʻOkina|ʻokina]] and five long vowels. However, [[Hawaiian Braille]] has only 13 letters.) While Rotokas has a small alphabet because it has few phonemes to represent (just eleven), Book Pahlavi was small because many letters had been ''conflated''—that is, the graphic distinctions had been lost over time, and diacritics were not developed to compensate for this as they were in [[Arabic alphabet|Arabic]], another script that lost many of its distinct letter shapes. For example, a comma-shaped letter represented ''g'', ''d'', ''y'', ''k'', or ''j''. However, such apparent simplifications can perversely make a script more complicated. In later Pahlavi [[papyrus|papyri]], up to half of the remaining graphic distinctions of these twelve letters were lost, and the script could no longer be read as a sequence of letters at all, but instead each word had to be learned as a whole—that is, they had become [[logogram]] as in Egyptian [[Demotic Egyptian|Demotic]]. The largest segmental script is probably an abugida, [[Devanagari]]. When written in Devanagari, Vedic [[Sanskrit]] has an alphabet of 53 letters, including the ''visarga'' mark for final aspiration and special letters for ''kš'' and ''jñ,'' though one of the letters is theoretical and not actually used. The Hindi alphabet must represent both Sanskrit and modern vocabulary, and so has been expanded to 58 with the ''khutma'' letters (letters with a dot added) to represent sounds from Persian and English. Thai has a total of 59 symbols, consisting of 44 consonants, 13 vowels and 2 syllabics, not including 4 diacritics for tone marks and one for vowel length. The largest known abjad is [[Sindhi language|Sindhi]], with 51 letters. The largest alphabets in the narrow sense include [[Kabardian language|Kabardian]] and [[Abkhaz language|Abkhaz]] (for [[Cyrillic]]), with 58 and 56 letters, respectively, and [[Slovak language|Slovak]] (for the [[Latin script]]), with 46. However, these scripts either count [[digraph (orthography)|di- and tri-graphs]] as separate letters, as Spanish did with ''ch'' and ''ll'' until recently, or uses [[diacritic]] like Slovak ''č''. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
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"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
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]
|
[
"Types"
]
| The [[Georgian alphabet]] ( '''') is an alphabetic writing system. With 33 letters, it is the largest true alphabet where each letter is graphically independent. The original Georgian alphabet had 38 letters but 5 letters were removed in the 19th century by [[Ilia Chavchavadze]]. The Georgian alphabet is much closer to Greek than the other Caucasian alphabets. The letter order parallels the Greek, with the consonants without a Greek equivalent organized at the end of the alphabet. The origins of the alphabet are still unknown. Some Armenian and Western scholars believe it was created by Mesrop Mashtots (Armenian: Մեսրոպ Մաշտոց Mesrop Maštoc') also known as Mesrob the Vartabed, who was an early medieval Armenian linguist, theologian, statesman and hymnologist, best known for inventing the Armenian alphabet c. 405 AD; other Georgian and Western scholars are against this theory. Most scholars link the creation of the Georgian script to the process of [[Christianization of Iberia]], a core Georgian kingdom of [[Kartli]]. The alphabet was therefore most probably created between the conversion of Iberia under King [[Mirian III of Iberia|Mirian III]] (326 or 337) and the [[Bir el Qutt inscriptions]] of 430, contemporaneously with the Armenian alphabet. Syllabaries typically contain 50 to 400 glyphs, and the glyphs of logographic systems typically number from the many hundreds into the thousands. Thus a simple count of the number of distinct symbols is an important clue to the nature of an unknown script. The [[Armenian alphabet]] ( '''' or '''') is a graphically unique alphabetical writing system that has been used to write the Armenian language. It was created in year 405 A.D. originally contained 36 letters. Two more letters, օ (o) and ֆ (f), were added in the Middle Ages. During the 1920s orthography reform, a new letter և (capital ԵՎ) was added, which was a ligature before ե+ւ, while the letter Ւ ւ was discarded and reintroduced as part of a new letter ՈՒ ու (which was a digraph before). The Armenian script's directionality is horizontal left-to-right, like the Latin and Greek alphabets. It also uses [[bicameral script]] like those. The Armenian word for "alphabet" is '''' (), named after the first two letters of the Armenian alphabet Ա այբ ayb and Բ բեն ben. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
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"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
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"Alphabetical order",
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"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
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|
[
"Alphabetical order"
]
| Alphabets often come to be associated with a standard ordering of their letters, which can then be used for purposes of [[collation]]—namely for the listing of words and other items in what is called ''[[alphabetical order]]''. The basic ordering of the [[Latin alphabet]] ([[A]] [[B]] [[C]] [[D]] [[E]] [[F]] [[G]] [[H]] [[I]] [[J]] [[K]] [[L]] [[M]] [[N]] [[O]] [[P]] [[Q]] [[R]] [[S]] [[T]] [[U]] [[V]] [[W]] [[X]] [[Y]] [[Z]]), which is derived from the Northwest Semitic "Abgad" order, is well established, although languages using this alphabet have different conventions for their treatment of modified letters (such as the [[French language|French]] ''é'', ''à'', and ''ô'') and of certain combinations of letters ([[Multigraph (orthography)|multigraphs]]). In French, these are not considered to be additional letters for the purposes of collation. However, in [[Icelandic language|Icelandic]], the accented letters such as ''á'', ''í'', and ''ö'' are considered distinct letters representing different vowel sounds from the sounds represented by their unaccented counterparts. In Spanish, ''ñ'' is considered a separate letter, but accented vowels such as ''á'' and ''é'' are not. The ''ll'' and ''ch'' were also considered single letters, but in 1994 the [[Real Academia Española]] changed the collating order so that ''ll'' is between ''lk'' and ''lm'' in the dictionary and ''ch'' is between ''cg'' and ''ci'', and in 2010 the tenth congress of the [[Association of Spanish Language Academies]] changed it so they were no longer letters at all. In German, words starting with ''sch-'' (which spells the German phoneme ) are inserted between words with initial ''sca-'' and ''sci-'' (all incidentally loanwords) instead of appearing after initial ''sz'', as though it were a single letter—in contrast to several languages such as [[Albanian alphabet|Albanian]], in which ''dh-'', ''ë-'', ''gj-'', ''ll-'', ''rr-'', ''th-'', ''xh-'' and ''zh-'' (all representing phonemes and considered separate single letters) would follow the letters ''d'', ''e'', ''g'', ''l'', ''n'', ''r'', ''t'', ''x'' and ''z'' respectively, as well as Hungarian and Welsh. Further, German words with an [[Diaeresis (diacritic)#Umlaut|umlaut]] are collated ignoring the umlaut—contrary to [[Turkish alphabet|Turkish]] that adopted the [[grapheme]] '''ö''' and '''ü''', and where a word like ''tüfek'', would come after ''tuz'', in the dictionary. An exception is the German telephone directory where umlauts are sorted like ''ä'' = ''ae'' since names such as ''Jäger'' also appear with the spelling ''Jaeger'', and are not distinguished in the spoken language. The [[Danish orthography|Danish]] and [[Norwegian orthography|Norwegian]] alphabets end with ''æ''—''ø''—''å'', whereas the Swedish and [[Finnish orthography|Finnish]] ones conventionally put ''å''—''ä''—''ö'' at the end. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
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"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
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"Alphabetical order",
"Acrophony",
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"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
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|
[
"Alphabetical order"
]
| It is unknown whether the earliest alphabets had a defined sequence. Some alphabets today, such as the [[Hanuno'o script]], are learned one letter at a time, in no particular order, and are not used for [[collation]] where a definite order is required. However, a dozen [[Ugaritic alphabet|Ugaritic]] tablets from the fourteenth century BC preserve the alphabet in two sequences. One, the ''ABCDE'' order later used in Phoenician, has continued with minor changes in [[Hebrew alphabet|Hebrew]], [[Greek alphabet|Greek]], [[Armenian alphabet|Armenian]], [[Gothic alphabet|Gothic]], [[Cyrillic]], and [[Latin alphabet|Latin]]; the other, ''HMĦLQ,'' was used in southern Arabia and is preserved today in [[Ge'ez alphabet|Ethiopic]]. Both orders have therefore been stable for at least 3000 years. [[Runic alphabet|Runic]] used an unrelated [[Elder Futhark|Futhark]] sequence, which was later [[Younger Futhark|simplified]]. [[Arabic alphabet|Arabic]] uses its own sequence, although Arabic retains the traditional [[abjadi order]] for numbering. The [[Brahmic family]] of alphabets used in India use a unique order based on [[phonology]]: The letters are arranged according to how and where they are produced in the mouth. This organization is used in Southeast Asia, Tibet, Korean [[hangul]], and even Japanese [[kana]], which is not an alphabet. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
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"Abecedarium",
"Alphabetical order",
"Acrophony",
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"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
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|
[
"Names of letters"
]
| The Phoenician letter names, in which each letter was associated with a word that begins with that sound ([[acrophony]]), continue to be used to varying degrees in [[Samaritan alphabet|Samaritan]], [[Aramaic alphabet|Aramaic]], [[Syriac alphabet|Syriac]], [[Hebrew alphabet|Hebrew]], [[Greek alphabet|Greek]] and [[Arabic alphabet|Arabic]]. The names were abandoned in [[Latin alphabet|Latin]], which instead referred to the letters by adding a vowel (usually e) before or after the consonant; the two exceptions were [[Y]] and [[Z]], which were borrowed from the Greek alphabet rather than Etruscan, and were known as ''Y Graeca'' "Greek Y" (pronounced ''I Graeca'' "Greek I") and ''zeta'' (from Greek)—this discrepancy was inherited by many European languages, as in the term ''zed'' for Z in all forms of English other than American English. Over time names sometimes shifted or were added, as in ''double U'' for [[W]] ("double V" in French), the English name for Y, and American ''zee'' for Z. Comparing names in English and French gives a clear reflection of the [[Great Vowel Shift]]: A, B, C and D are pronounced in today's English, but in contemporary French they are . The French names (from which the English names are derived) preserve the qualities of the English vowels from before the Great Vowel Shift. By contrast, the names of F, L, M, N and S () remain the same in both languages, because "short" vowels were largely unaffected by the Shift. In Cyrillic originally the letters were given names based on Slavic words; this was later abandoned as well in favor of a system similar to that used in Latin. Letters of [[Armenian alphabet]] also have distinct letter names. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
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"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
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"Abecedarium",
"Alphabetical order",
"Acrophony",
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"List of alphabets",
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"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
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|
[
"Orthography and pronunciation"
]
| When an alphabet is adopted or developed to represent a given language, an [[orthography]] generally comes into being, providing rules for the [[spelling]] of words in that language. In accordance with the principle on which alphabets are based, these rules will generally map letters of the alphabet to the [[phoneme]] (significant sounds) of the spoken language. In a perfectly [[phonemic orthography]] there would be a consistent one-to-one correspondence between the letters and the phonemes, so that a writer could predict the spelling of a word given its pronunciation, and a speaker would always know the pronunciation of a word given its spelling, and vice versa. However this ideal is not usually achieved in practice; some languages (such as [[Spanish language|Spanish]] and [[Finnish language|Finnish]]) come close to it, while others (such as English) deviate from it to a much larger degree. The pronunciation of a language often evolves independently of its writing system, and writing systems have been borrowed for languages they were not designed for, so the degree to which letters of an alphabet correspond to phonemes of a language varies greatly from one language to another and even within a single language. Languages may fail to achieve a one-to-one correspondence between letters and sounds in any of several ways: (-) A language may represent a given phoneme by a combination of letters rather than just a single letter. Two-letter combinations are called [[digraph (orthography)|digraphs]] and three-letter groups are called [[trigraph (orthography)|trigraphs]]. [[German language|German]] uses the [[tetragraph]] (four letters) "tsch" for the phoneme and (in a few borrowed words) "dsch" for . [[Kabardian language|Kabardian]] also uses a tetragraph for one of its phonemes, namely "кхъу". Two letters representing one sound occur in several instances in Hungarian as well (where, for instance, ''cs'' stands for [tʃ], ''sz'' for [s], ''zs'' for [ʒ], ''dzs'' for [dʒ]). (-) A language may represent the same phoneme with two or more different letters or combinations of letters. An example is [[modern Greek]] which may write the phoneme in six different ways: , , , , , and (though the last is rare). (-) A language may spell some words with unpronounced letters that exist for historical or other reasons. For example, the spelling of the Thai word for "beer" [เบียร์] retains a letter for the final consonant "r" present in the English word it was borrowed from, but silences it. (-) Pronunciation of individual words may change according to the presence of surrounding words in a sentence ([[sandhi]]). (-) Different dialects of a language may use different phonemes for the same word. (-) A language may use different sets of symbols or different rules for distinct sets of vocabulary items, such as the Japanese [[hiragana]] and [[katakana]] syllabaries, or the various rules in English for spelling words from Latin and Greek, or the original [[Germanic languages|Germanic]] vocabulary. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
"Alphabet effect",
"Constructed script",
"List of alphabets",
"Unicode",
"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[
"Orthography and pronunciation"
]
| National languages sometimes elect to address the problem of dialects by simply associating the alphabet with the national standard. Some national languages like [[Finnish language|Finnish]], [[Armenian language|Armenian]], [[Turkish language|Turkish]], [[Russian language|Russian]], [[Serbo-Croatian language|Serbo-Croatian]] ([[Serbian language|Serbian]], [[Croatian language|Croatian]] and [[Bosnian language|Bosnian]]) and [[Bulgarian language|Bulgarian]] have a very regular spelling system with a nearly one-to-one correspondence between letters and phonemes. Strictly speaking, these national languages lack a word corresponding to the verb "to spell" (meaning to split a word into its letters), the closest match being a verb meaning to split a word into its syllables. Similarly, the [[Italian language|Italian]] verb corresponding to 'spell (out)', ''compitare'', is unknown to many Italians because spelling is usually trivial, as Italian spelling is highly phonemic. In standard [[Spanish language|Spanish]], one can tell the pronunciation of a word from its spelling, but not vice versa, as certain phonemes can be represented in more than one way, but a given letter is consistently pronounced. [[French language|French]], with its [[silent letter]] and its heavy use of [[nasal vowel]] and [[elision]], may seem to lack much correspondence between spelling and pronunciation, but its rules on pronunciation, though complex, are actually consistent and predictable with a fair degree of accuracy. At the other extreme are languages such as English, where the pronunciations of many words simply have to be memorized as they do not correspond to the spelling in a consistent way. For English, this is partly because the [[Great Vowel Shift]] occurred after the orthography was established, and because English has acquired a large number of loanwords at different times, retaining their original spelling at varying levels. Even English has general, albeit complex, rules that predict pronunciation from spelling, and these rules are successful most of the time; rules to predict spelling from the pronunciation have a higher failure rate. Sometimes, countries have the written language undergo a [[spelling reform]] to realign the writing with the contemporary spoken language. These can range from simple spelling changes and word forms to switching the entire writing system itself, as when [[Turkey]] switched from the Arabic alphabet to a Latin-based [[Turkish alphabet]]. The standard system of symbols used by [[linguist]] to represent sounds in any language, independently of orthography, is called the [[International Phonetic Alphabet]]. | 670 | Alphabet | [
"Alphabets",
"Orthography"
]
| [
"Akshara",
"Lipogram",
"ICAO (NATO) spelling alphabet",
"Pangram",
"Alphabet book",
"A Is For Aardvark",
"Hangul",
"Abecedarium",
"Alphabetical order",
"Acrophony",
"Alphabet effect",
"Constructed script",
"List of alphabets",
"Unicode",
"Thai script",
"Butterfly Alphabet",
"English alphabet",
"Transliteration",
"Cyrillic",
"Alphabet song",
"Thoth",
"Character encoding"
]
|
[]
| [[Image:Bohr atom model.svg|thumb|right|300px|The '''Rutherford–Bohr model''' of the [[hydrogen atom]] () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of the electromagnetic radiation emitted (shown) when an electron jumps from one orbital to another be proportional to the mathematical square of atomic charge (). Experimental measurement by [[Henry Moseley]] of this radiation for many elements (from ) showed the results as predicted by Bohr. Both the concept of atomic number and the Bohr model were thereby given scientific credence.]] The '''atomic number''' or '''proton number''' (symbol ''Z'') of a [[chemical element]] is the number of [[proton]] found in the [[atomic nucleus|nucleus]] of every [[atom]] of that element. The atomic number uniquely identifies a [[chemical element]]. It is identical to the [[charge number]] of the nucleus. In an [[electric charge|uncharged]] atom, the atomic number is also equal to the number of [[electron]]. The sum of the atomic number ''Z'' and the [[neutron number|number of neutrons]] ''N'' gives the [[mass number]] ''A'' of an atom. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes) and the [[Binding energy#Mass change|mass defect]] of [[nucleon]] binding is always small compared to the nucleon mass, the [[atomic mass]] of any atom, when expressed in [[Atomic mass unit|unified atomic mass units]] (making a quantity called the "[[atomic mass|relative isotopic mass]]"), is within 1% of the whole number ''A''. Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as [[isotope]]. A little more than three-quarters of naturally occurring elements exist as a mixture of isotopes (see [[monoisotopic element]]), and the average isotopic mass of an isotopic mixture for an element (called the relative atomic mass) in a defined environment on Earth, determines the element's standard [[atomic weight]]. Historically, it was these atomic weights of elements (in comparison to hydrogen) that were the quantities measurable by chemists in the 19th century. The conventional symbol ''Z'' comes from the [[German language|German]] word meaning ''number'', which, before the modern synthesis of ideas from chemistry and physics, merely denoted an element's numerical place in the [[periodic table]], whose order is approximately, but not completely, consistent with the order of the elements by atomic weights. Only after 1915, with the suggestion and evidence that this ''Z'' number was also the nuclear charge and a physical characteristic of atoms, did the word (and its English equivalent ''atomic number'') come into common use in this context. | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"History",
"The periodic table and a natural number for each element"
]
| Loosely speaking, the existence or construction of a [[periodic table]] of elements creates an ordering of the elements, and so they can be numbered in order. [[Dmitri Mendeleev]] claimed that he arranged his first periodic tables (first published on March 6, 1869) in order of [[atomic weight]] ("Atomgewicht"). However, in consideration of the elements' observed chemical properties, he changed the order slightly and placed [[tellurium]] (atomic weight 127.6) ahead of [[iodine]] (atomic weight 126.9). This placement is consistent with the modern practice of ordering the elements by proton number, ''Z'', but that number was not known or suspected at the time. A simple numbering based on periodic table position was never entirely satisfactory, however. Besides the case of iodine and tellurium, later several other pairs of elements (such as [[argon]] and [[potassium]], [[cobalt]] and [[nickel]]) were known to have nearly identical or reversed atomic weights, thus requiring their placement in the periodic table to be determined by their chemical properties. However the gradual identification of more and more chemically similar [[lanthanide]] elements, whose atomic number was not obvious, led to inconsistency and uncertainty in the periodic numbering of elements at least from [[lutetium]] (element 71) onward ([[hafnium]] was not known at this time). | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"History",
"The Rutherford-Bohr model and van den Broek"
]
| In 1911, [[Ernest Rutherford]] gave a [[Rutherford model|model]] of the atom in which a central nucleus held most of the atom's mass and a positive charge which, in units of the electron's charge, was to be approximately equal to half of the atom's atomic weight, expressed in numbers of hydrogen atoms. This central charge would thus be approximately half the atomic weight (though it was almost 25% different from the atomic number of gold , ), the single element from which Rutherford made his guess). Nevertheless, in spite of Rutherford's estimation that gold had a central charge of about 100 (but was element on the periodic table), a month after Rutherford's paper appeared, [[Antonius van den Broek]] first formally suggested that the central charge and number of electrons in an atom was ''exactly'' equal to its place in the periodic table (also known as element number, atomic number, and symbolized ''Z''). This proved eventually to be the case. | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"History",
"Moseley's 1913 experiment"
]
| The experimental position improved dramatically after research by [[Henry Moseley]] in 1913. Moseley, after discussions with Bohr who was at the same lab (and who had used Van den Broek's hypothesis in his [[Bohr model]] of the atom), decided to test Van den Broek's and Bohr's hypothesis directly, by seeing if [[spectral line]] emitted from excited atoms fitted the Bohr theory's postulation that the frequency of the spectral lines be proportional to the square of ''Z''. To do this, Moseley measured the wavelengths of the innermost photon transitions (K and L lines) produced by the elements from aluminum (''Z'' = 13) to gold (''Z'' = 79) used as a series of movable anodic targets inside an [[x-ray tube]]. The square root of the frequency of these photons increased from one target to the next in an arithmetic progression. This led to the conclusion ([[Moseley's law]]) that the atomic number does closely correspond (with an offset of one unit for K-lines, in Moseley's work) to the calculated [[electric charge]] of the nucleus, i.e. the element number ''Z''. Among other things, Moseley demonstrated that the [[lanthanide]] series (from [[lanthanum]] to [[lutetium]] inclusive) must have 15 members—no fewer and no more—which was far from obvious from known chemistry at that time. | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"History",
"Missing elements"
]
| After Moseley's death in 1915, the atomic numbers of all known elements from hydrogen to uranium (''Z'' = 92) were examined by his method. There were seven elements (with ''Z'' < 92) which were not found and therefore identified as still undiscovered, corresponding to atomic numbers 43, 61, 72, 75, 85, 87 and 91. From 1918 to 1947, all seven of these missing elements were discovered. By this time, the first four transuranium elements had also been discovered, so that the periodic table was complete with no gaps as far as curium (''Z'' = 96). | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"History",
"The proton and the idea of nuclear electrons"
]
| In 1915, the reason for nuclear charge being quantized in units of ''Z'', which were now recognized to be the same as the element number, was not understood. An old idea called [[Prout's hypothesis]] had postulated that the elements were all made of residues (or "protyles") of the lightest element hydrogen, which in the Bohr-Rutherford model had a single electron and a nuclear charge of one. However, as early as 1907, Rutherford and [[Thomas Royds]] had shown that alpha particles, which had a charge of +2, were the nuclei of helium atoms, which had a mass four times that of hydrogen, not two times. If Prout's hypothesis were true, something had to be neutralizing some of the charge of the hydrogen nuclei present in the nuclei of heavier atoms. In 1917, Rutherford succeeded in generating hydrogen nuclei from a [[nuclear reaction]] between alpha particles and nitrogen gas, and believed he had proven Prout's law. He called the new heavy nuclear particles protons in 1920 (alternate names being proutons and protyles). It had been immediately apparent from the work of Moseley that the nuclei of heavy atoms have more than twice as much mass as would be expected from their being made of [[hydrogen]] nuclei, and thus there was required a hypothesis for the neutralization of the extra [[protons]] presumed present in all heavy nuclei. A helium nucleus was presumed to be composed of four protons plus two "nuclear electrons" (electrons bound inside the nucleus) to cancel two of the charges. At the other end of the periodic table, a nucleus of gold with a mass 197 times that of hydrogen was thought to contain 118 nuclear electrons in the nucleus to give it a residual charge of +79, consistent with its atomic number. | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"History",
"The discovery of the neutron makes ''Z'' the proton number"
]
| All consideration of nuclear electrons ended with [[James Chadwick]]'s [[discovery of the neutron]] in 1932. An atom of gold now was seen as containing 118 neutrons rather than 118 nuclear electrons, and its positive charge now was realized to come entirely from a content of 79 protons. After 1932, therefore, an element's atomic number ''Z'' was also realized to be identical to the [[proton number]] of its nuclei. | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"The symbol of ''Z''"
]
| The conventional symbol ''Z'' possibly comes from the [[German language|German]] word (atomic number). However, prior to 1915, the word ''Zahl'' (simply ''number'') was used for an element's assigned number in the periodic table. | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"Chemical properties"
]
| Each element has a specific set of chemical properties as a consequence of the number of electrons present in the neutral atom, which is ''Z'' (the atomic number). The [[electron configuration|configuration]] of these electrons follows from the principles of [[quantum mechanics]]. The number of electrons in each element's [[electron shell]], particularly the outermost [[valence shell]], is the primary factor in determining its [[chemical bonding]] behavior. Hence, it is the atomic number alone that determines the chemical properties of an element; and it is for this reason that an element can be defined as consisting of ''any'' mixture of atoms with a given atomic number. | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[
"New elements"
]
| The quest for new elements is usually described using atomic numbers. As of , all elements with atomic numbers 1 to 118 have been observed. Synthesis of new elements is accomplished by bombarding target atoms of heavy elements with ions, such that the sum of the atomic numbers of the target and ion elements equals the atomic number of the element being created. In general, the [[half-life]] of a [[nuclide]] becomes shorter as atomic number increases, though undiscovered nuclides with certain "[[magic number (physics)|magic]]" numbers of protons and neutrons may have relatively longer half-lives and comprise an [[island of stability]]. | 673 | Atomic number | [
"Chemical properties",
"Nuclear physics",
"Atoms",
"Dimensionless numbers of chemistry",
"Numbers"
]
| [
"Mass number",
"Atomic theory",
"List of elements by atomic number",
"Prout's hypothesis",
"Effective atomic number",
"Chemical element",
"History of the periodic table",
"Neutron number"
]
|
[]
| '''Anatomy''' (Greek ''anatomē'', 'dissection') is the branch of [[biology]] concerned with the study of the structure of [[organism]] and their parts. Anatomy is a branch of natural [[science]] which deals with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. Anatomy is inherently tied to [[developmental biology]], [[embryology]], [[comparative anatomy]], [[evolutionary biology]], and [[phylogeny]], as these are the processes by which anatomy is generated, both over immediate and long-term timescales. Anatomy and [[physiology]], which study the structure and [[function (biology)|function]] of organisms and their parts respectively, make a natural pair of [[multidisciplinary approach|related disciplines]], and are often studied together. [[Human body|Human anatomy]] is one of the essential [[basic sciences]] that are [[Applied science|applied]] in [[medicine]]. The discipline of anatomy is divided into [[macroscopic scale|macroscopic]] and [[microscopic scale|microscopic]]. [[Gross anatomy|Macroscopic anatomy]], or [[gross anatomy]], is the examination of an animal's body parts using unaided [[eyesight]]. Gross anatomy also includes the branch of [[superficial anatomy]]. Microscopic anatomy involves the use of optical instruments in the study of the [[tissue (biology)|tissues]] of various structures, known as [[histology]], and also in the study of [[cell biology|cells]]. The [[history of anatomy]] is characterized by a progressive understanding of the functions of the [[organ (anatomy)|organs]] and structures of the human body. Methods have also improved dramatically, advancing from the examination of animals by [[dissection]] of carcasses and [[cadaver]] (corpses) to 20th century [[medical imaging]] techniques including [[Radiography|X-ray]], [[Ultrasound imaging|ultrasound]], and [[magnetic resonance imaging]]. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Definition"
]
| Derived from the [[Ancient Greek|Greek]] ''anatomē'' "dissection" (from ''anatémnō'' "I cut up, cut open" from ἀνά ''aná'' "up", and τέμνω ''témnō'' "I cut"), anatomy is the scientific study of the structure of [[organism]] including their systems, organs and [[tissue (biology)|tissues]]. It includes the appearance and position of the various parts, the materials from which they are composed, their locations and their relationships with other parts. Anatomy is quite distinct from [[physiology]] and [[biochemistry]], which deal respectively with the functions of those parts and the chemical processes involved. For example, an anatomist is concerned with the shape, size, position, structure, blood supply and innervation of an organ such as the liver; while a physiologist is interested in the production of [[bile]], the role of the liver in nutrition and the regulation of bodily functions. The discipline of anatomy can be subdivided into a number of branches including gross or [[Macroscopic scale|macroscopic]] anatomy and [[Microscopic scale|microscopic]] anatomy. [[Gross anatomy]] is the study of structures large enough to be seen with the naked eye, and also includes [[superficial anatomy]] or surface anatomy, the study by sight of the external body features. [[Microscopic anatomy]] is the study of structures on a microscopic scale, along with [[histology]] (the study of tissues), and [[embryology]] (the study of an organism in its immature condition). Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs and systems. Methods used include [[dissection]], in which a body is opened and its organs studied, and [[endoscopy]], in which a [[video camera]]-equipped instrument is inserted through a small incision in the body wall and used to explore the internal organs and other structures. [[Angiography]] using [[X-ray]] or [[magnetic resonance angiography]] are methods to visualize blood vessels. The term "anatomy" is commonly taken to refer to [[human anatomy]]. However, substantially the same structures and tissues are found throughout the rest of the animal kingdom and the term also includes the anatomy of other animals. The term ''zootomy'' is also sometimes used to specifically refer to non-human animals. The structure and tissues of plants are of a dissimilar nature and they are studied in [[plant anatomy]]. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Animal tissues"
]
| The [[Kingdom (biology)|kingdom]] [[Animalia]] contains [[multicellular organism]] that are [[heterotroph]] and [[Motility|motile]] (although some have secondarily adopted a [[Sessility (zoology)|sessile]] lifestyle). Most animals have bodies differentiated into separate [[Tissue (biology)|tissues]] and these animals are also known as [[eumetazoa]]. They have an internal [[digestion|digestive]] chamber, with one or two openings; the [[gamete]] are produced in multicellular sex organs, and the [[zygote]] include a [[blastula]] stage in their [[Embryogenesis|embryonic development]]. Metazoans do not include the [[sponge]], which have undifferentiated cells. Unlike [[plant cell]], [[animal cells]] have neither a cell wall nor [[chloroplast]]. Vacuoles, when present, are more in number and much smaller than those in the plant cell. The body tissues are composed of numerous types of cell, including those found in [[muscle]], [[nerve]] and [[skin]]. Each typically has a cell membrane formed of [[phospholipid]], [[cytoplasm]] and a [[Cell nucleus|nucleus]]. All of the different cells of an animal are derived from the embryonic [[germ layer]]. Those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called [[diploblasty|diploblastic]] and the more developed animals whose structures and organs are formed from three germ layers are called [[triploblasty|triploblastic]]. All of a triploblastic animal's tissues and organs are derived from the three germ layers of the embryo, the [[ectoderm]], [[mesoderm]] and [[endoderm]]. Animal tissues can be grouped into four basic types: [[connective tissue|connective]], [[epithelium|epithelial]], [[muscle tissue|muscle]] and [[nervous tissue]]. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Animal tissues",
"Connective tissue"
]
| [[Connective tissue]] are fibrous and made up of cells scattered among inorganic material called the [[extracellular matrix]]. Connective tissue gives shape to organs and holds them in place. The main types are loose connective tissue, [[adipose tissue]], fibrous connective tissue, [[cartilage]] and [[bone]]. The extracellular matrix contains [[protein]], the chief and most abundant of which is [[collagen]]. Collagen plays a major part in organizing and maintaining tissues. The matrix can be modified to form a [[skeleton]] to support or protect the body. An [[exoskeleton]] is a thickened, rigid [[cuticle]] which is stiffened by [[mineralisation (biology)|mineralization]], as in [[crustacean]] or by the cross-linking of its proteins as in [[insect]]. An [[endoskeleton]] is internal and present in all developed animals, as well as in many of those less developed. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Animal tissues",
"Epithelium"
]
| [[Epithelial tissue]] is composed of closely packed cells, bound to each other by [[cell adhesion molecule]], with little intercellular space. Epithelial cells can be [[Squamous epithelial cell|squamous]] (flat), [[Simple cuboidal epithelium|cuboidal]] or [[Columnar epithelial cell|columnar]] and rest on a [[basal lamina]], the upper layer of the [[basement membrane]], the lower layer is the reticular lamina lying next to the connective tissue in the extracellular matrix secreted by the epithelial cells. There are many different types of epithelium, modified to suit a particular function. In the [[respiratory tract]] there is a type of [[pseudostratified ciliated columnar epithelium|ciliated]] epithelial lining; in the small intestine there are [[Microvillus|microvilli]] on the epithelial lining and in the large intestine there are [[Intestinal villus|intestinal villi]]. [[Skin]] consists of an outer layer of [[keratin]] stratified squamous epithelium that covers the exterior of the vertebrate body. [[Keratinocyte]] make up to 95% of the cells in the [[epidermis (skin)|skin]]. The epithelial cells on the external surface of the body typically secrete an extracellular matrix in the form of a [[cuticle]]. In simple animals this may just be a coat of [[glycoproteins]]. In more advanced animals, many [[gland]] are formed of epithelial cells. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Animal tissues",
"Muscle tissue"
]
| [[Myocyte|Muscle cells]] (myocytes) form the active contractile tissue of the body. [[Muscle tissue]] functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle is formed of contractile [[Myofibril|filaments]] and is separated into three main types; [[Smooth muscle tissue|smooth muscle]], [[Skeletal striated muscle|skeletal muscle]] and [[cardiac muscle]]. Smooth muscle has no [[Striated muscle tissue|striations]] when examined microscopically. It contracts slowly but maintains contractibility over a wide range of stretch lengths. It is found in such organs as [[sea anemone]] tentacles and the body wall of [[sea cucumber]]. Skeletal muscle contracts rapidly but has a limited range of extension. It is found in the movement of appendages and jaws. Obliquely striated muscle is intermediate between the other two. The filaments are staggered and this is the type of muscle found in [[earthworm]] that can extend slowly or make rapid contractions. In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets. Smooth muscle is found in the walls of the [[uterus]], [[bladder]], [[intestines]], [[stomach]], [[oesophagus]], [[respiratory airways]], and [[blood vessel]]. [[Cardiac muscle]] is found only in the [[heart]], allowing it to contract and pump blood round the body. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Animal tissues",
"Nervous tissue"
]
| [[Nervous tissue]] is composed of many nerve cells known as [[neuron]] which transmit information. In some slow-moving [[Radial symmetry|radially symmetrical]] marine animals such as [[ctenophore]] and [[cnidarian]] (including [[sea anemone]] and [[jellyfish]]), the nerves form a [[nerve net]], but in most animals they are organized longitudinally into bundles. In simple animals, receptor neurons in the body wall cause a local reaction to a stimulus. In more complex animals, specialized receptor cells such as [[chemoreceptor]] and [[photoreceptor cell|photoreceptors]] are found in groups and send messages along [[biological neural network|neural networks]] to other parts of the organism. Neurons can be connected together in [[Ganglion|ganglia]]. In higher animals, specialized receptors are the basis of sense organs and there is a [[central nervous system]] (brain and spinal cord) and a [[peripheral nervous system]]. The latter consists of [[Sensory neuron|sensory nerves]] that transmit information from sense organs and [[Motor neuron|motor nerves]] that influence target organs. The peripheral nervous system is divided into the [[somatic nervous system]] which conveys sensation and controls [[voluntary muscle]], and the [[autonomic nervous system]] which involuntarily controls [[smooth muscle]], certain glands and internal organs, including the [[stomach]]. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Vertebrate anatomy"
]
| All [[vertebrate]] have a similar basic [[body plan]] and at some point in their lives, mostly in the [[embryogenesis|embryonic]] stage, share the major [[chordate]] characteristics; a stiffening rod, the [[notochord]]; a dorsal hollow tube of nervous material, the [[neural tube]]; [[pharyngeal arch]]; and a tail posterior to the anus. The [[spinal cord]] is protected by the [[vertebral column]] and is above the notochord and the [[Gut (anatomy)|gastrointestinal tract]] is below it. Nervous tissue is derived from the [[ectoderm]], connective tissues are derived from [[mesoderm]], and gut is derived from the [[endoderm]]. At the posterior end is a [[tail]] which continues the spinal cord and vertebrae but not the gut. The mouth is found at the anterior end of the animal, and the [[anus]] at the base of the tail. The defining characteristic of a vertebrate is the [[vertebral column]], formed in the development of the segmented series of [[vertebra]]. In most vertebrates the notochord becomes the [[nucleus pulposus]] of the [[intervertebral disc]]. However, a few vertebrates, such as the [[sturgeon]] and the [[coelacanth]] retain the notochord into adulthood. [[Gnathostomata|Jawed vertebrates]] are typified by paired appendages, fins or legs, which may be secondarily lost. The limbs of vertebrates are considered to be [[Homology (biology)|homologous]] because the same underlying skeletal structure was inherited from their last common ancestor. This is one of the arguments put forward by [[Charles Darwin]] to support his theory of [[evolution]]. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Vertebrate anatomy",
"Fish anatomy"
]
| The body of a [[fish]] is divided into a head, trunk and tail, although the divisions between the three are not always externally visible. The skeleton, which forms the support structure inside the fish, is either made of cartilage, in [[cartilaginous fish]], or bone in [[bony fish]]. The main skeletal element is the vertebral column, composed of articulating [[vertebra]] which are lightweight yet strong. The ribs attach to the spine and there are no [[Limb (anatomy)|limbs]] or limb girdles. The main external features of the fish, the [[fish fin|fins]], are composed of either bony or soft spines called rays, which with the exception of the [[caudal fin]], have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk. The heart has two chambers and pumps the blood through the respiratory surfaces of the [[gill]] and on round the body in a single circulatory loop. The eyes are adapted for seeing underwater and have only local vision. There is an inner ear but no external or [[middle ear]]. Low frequency vibrations are detected by the [[lateral line]] system of sense organs that run along the length of the sides of fish, and these respond to nearby movements and to changes in water pressure. Sharks and rays are [[Basal (phylogenetics)|basal]] fish with numerous [[Primitive (phylogenetics)|primitive]] anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head. The dermis is covered with separate dermal [[placoid scales]]. They have a [[cloaca]] into which the urinary and genital passages open, but not a [[swim bladder]]. Cartilaginous fish produce a small number of large, [[Egg yolk|yolky]] eggs. Some species are [[ovoviviparous]] and the young develop internally but others are [[oviparous]] and the larvae develop externally in egg cases. The bony fish lineage shows more [[Derived trait|derived]] anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an [[operculum (fish)|operculum]], and a mouth at or near the tip of the snout. The dermis is covered with overlapping [[Fish scale|scales]]. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. They mostly [[Spawn (biology)|spawn]] a large number of small eggs with little yolk which they broadcast into the water column. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Vertebrate anatomy",
"Amphibian anatomy"
]
| [[Amphibian]] are a [[Class (biology)|class]] of animals comprising [[frog]], [[salamander]] and [[caecilian]]. They are [[tetrapod]], but the caecilians and a few species of salamander have either no limbs or their limbs are much reduced in size. Their main bones are hollow and lightweight and are fully ossified and the vertebrae interlock with each other and have [[articular processes]]. Their ribs are usually short and may be fused to the vertebrae. Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little [[keratin]] and lacks scales, but contains many [[mucous gland]] and in some species, poison glands. The hearts of amphibians have three chambers, two [[atrium (heart)|atria]] and one [[ventricle (heart)|ventricle]]. They have a [[urinary bladder]] and [[metabolic waste#nitrogen wastes|nitrogenous waste products]] are excreted primarily as [[urea]]. Amphibians breathe by means of [[buccal pumping]], a pump action in which air is first drawn into the [[Buccopharyngeal membrane|buccopharyngeal]] region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat. They supplement this with [[gas exchange]] through the skin which needs to be kept moist. In frogs the pelvic girdle is robust and the hind legs are much longer and stronger than the forelimbs. The feet have four or five digits and the toes are often webbed for swimming or have suction pads for climbing. Frogs have large eyes and no tail. Salamanders resemble lizards in appearance; their short legs project sideways, the belly is close to or in contact with the ground and they have a long tail. Caecilians superficially resemble [[earthworm]] and are limbless. They burrow by means of zones of muscle contractions which move along the body and they swim by undulating their body from side to side. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Vertebrate anatomy",
"Reptile anatomy"
]
| '''[[Reptile]]''' are a class of animals comprising [[turtle]], [[tuatara]], [[lizard]], [[snake]] and [[crocodile]]. They are [[tetrapod]], but the snakes and a few species of [[lizard]] either have no limbs or their limbs are much reduced in size. Their bones are better ossified and their skeletons stronger than those of amphibians. The teeth are conical and mostly uniform in size. The surface cells of the epidermis are modified into horny scales which create a waterproof layer. Reptiles are unable to use their skin for respiration as do amphibians and have a more efficient respiratory system drawing air into their [[lung]] by expanding their chest walls. The heart resembles that of the amphibian but there is a septum which more completely separates the oxygenated and deoxygenated bloodstreams. The reproductive system has evolved for internal fertilization, with a [[Sex organ|copulatory organ]] present in most species. The eggs are surrounded by [[Amniote|amniotic membranes]] which prevents them from drying out and are laid on land, or [[Ovoviviparity|develop internally]] in some species. The bladder is small as nitrogenous waste is excreted as [[uric acid]]. '''[[Turtles]]''' are notable for their protective shells. They have an inflexible trunk encased in a horny [[carapace]] above and a [[plastron]] below. These are formed from bony plates embedded in the dermis which are overlain by horny ones and are partially fused with the ribs and spine. The neck is long and flexible and the head and the legs can be drawn back inside the shell. Turtles are vegetarians and the typical reptile teeth have been replaced by sharp, horny plates. In aquatic species, the front legs are modified into flippers. '''[[Tuataras]]''' superficially resemble lizards but the lineages diverged in the [[Triassic]] period. There is one living species, ''[[Sphenodon punctatus]]''. The skull has two openings (fenestrae) on either side and the jaw is rigidly attached to the skull. There is one row of teeth in the lower jaw and this fits between the two rows in the upper jaw when the animal chews. The teeth are merely projections of bony material from the jaw and eventually wear down. The brain and heart are more primitive than those of other reptiles, and the lungs have a single chamber and lack [[Bronchus|bronchi]]. The tuatara has a well-developed [[parietal eye]] on its forehead. '''[[Lizards]]''' have skulls with only one [[Nasal fenestra|fenestra]] on each side, the lower bar of bone below the second fenestra having been lost. This results in the jaws being less rigidly attached which allows the mouth to open wider. Lizards are mostly quadrupeds, with the trunk held off the ground by short, sideways-facing legs, but a few species have no limbs and resemble snakes. Lizards have moveable eyelids, eardrums are present and some species have a central parietal eye. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Vertebrate anatomy",
"Reptile anatomy"
]
| '''[[Snakes]]''' are closely related to lizards, having branched off from a common ancestral lineage during the [[Cretaceous]] period, and they share many of the same features. The skeleton consists of a skull, a hyoid bone, spine and ribs though a few species retain a vestige of the pelvis and rear limbs in the form of [[pelvic spur]]. The bar under the second fenestra has also been lost and the jaws have extreme flexibility allowing the snake to swallow its prey whole. Snakes lack moveable eyelids, the eyes being covered by transparent "spectacle" scales. They do not have eardrums but can detect ground vibrations through the bones of their skull. Their forked tongues are used as organs of taste and smell and some species have sensory pits on their heads enabling them to locate warm-blooded prey. '''[[Crocodilians]]''' are large, low-slung aquatic reptiles with long snouts and large numbers of teeth. The head and trunk are dorso-ventrally flattened and the tail is laterally compressed. It undulates from side to side to force the animal through the water when swimming. The tough keratinized scales provide body armour and some are fused to the skull. The nostrils, eyes and ears are elevated above the top of the flat head enabling them to remain above the surface of the water when the animal is floating. Valves seal the nostrils and ears when it is submerged. Unlike other reptiles, crocodilians have hearts with four chambers allowing complete separation of oxygenated and deoxygenated blood. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Vertebrate anatomy",
"Bird anatomy"
]
| [[Birds]] are [[tetrapod]] but though their hind limbs are used for walking or hopping, their front limbs are [[wing]] covered with [[feather]] and adapted for flight. Birds are [[endotherm]], have a high [[metabolic rate]], a light [[Skeleton|skeletal system]] and powerful [[muscle]]. The long bones are thin, hollow and very light. Air sac extensions from the lungs occupy the centre of some bones. The sternum is wide and usually has a keel and the caudal vertebrae are fused. There are no teeth and the narrow jaws are adapted into a horn-covered beak. The eyes are relatively large, particularly in nocturnal species such as owls. They face forwards in predators and sideways in ducks. The feathers are outgrowths of the [[epidermis (zoology)|epidermis]] and are found in localized bands from where they fan out over the skin. Large flight feathers are found on the wings and tail, contour feathers cover the bird's surface and fine down occurs on young birds and under the contour feathers of water birds. The only cutaneous gland is the single [[uropygial gland]] near the base of the tail. This produces an oily secretion that waterproofs the feathers when the bird [[personal grooming|preens]]. There are scales on the legs, feet and claws on the tips of the toes. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Vertebrate anatomy",
"Mammal anatomy"
]
| [[Mammal]] are a diverse class of animals, mostly terrestrial but some are aquatic and others have evolved flapping or gliding flight. They mostly have four limbs but some aquatic mammals have no limbs or limbs modified into fins and the forelimbs of bats are modified into wings. The legs of most mammals are situated below the trunk, which is held well clear of the ground. The bones of mammals are well ossified and their teeth, which are usually differentiated, are coated in a layer of [[Tooth enamel|prismatic enamel]]. The teeth are shed once ([[Deciduous teeth|milk teeth]]) during the animal's lifetime or not at all, as is the case in [[cetacea]]. Mammals have three bones in the middle ear and a [[cochlea]] in the [[inner ear]]. They are clothed in hair and their skin contains glands which secrete [[sweat gland|sweat]]. Some of these glands are specialized as [[mammary gland]], producing milk to feed the young. Mammals breathe with [[lung]] and have a muscular [[Thoracic diaphragm|diaphragm]] separating the thorax from the abdomen which helps them draw air into the lungs. The mammalian heart has four chambers and oxygenated and deoxygenated blood are kept entirely separate. Nitrogenous waste is excreted primarily as urea. Mammals are [[amniote]], and most are [[Viviparity|viviparous]], giving birth to live young. The exception to this are the egg-laying [[monotreme]], the [[platypus]] and the [[echidna]] of Australia. Most other mammals have a [[placenta]] through which the developing [[foetus]] obtains nourishment, but in [[marsupial]], the foetal stage is very short and the immature young is born and finds its way to its mother's [[Pouch (marsupial)|pouch]] where it latches on to a [[nipple]] and completes its development. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Vertebrate anatomy",
"Mammal anatomy",
"Human anatomy"
]
| Humans have the overall body plan of a mammal. Humans have a [[human head|head]], [[neck]], [[Trunk (anatomy)|trunk]] (which includes the [[thorax]] and [[abdomen]]), two [[arm]] and [[hand]], and two [[human leg|legs]] and [[foot|feet]]. Generally, students of certain [[biology|biological sciences]], [[paramedic]], prosthetists and orthotists, [[physical therapy|physiotherapists]], [[occupational therapy|occupational therapists]], [[nursing|nurses]], [[podiatry|podiatrists]], and [[medical school|medical students]] learn gross anatomy and microscopic anatomy from anatomical models, skeletons, textbooks, diagrams, photographs, lectures and tutorials and in addition, medical students generally also learn gross anatomy through practical experience of [[dissection]] and inspection of [[cadaver]]. The study of microscopic anatomy (or [[histology]]) can be aided by practical experience examining histological preparations (or slides) under a [[microscope]]. Human anatomy, physiology and biochemistry are complementary basic medical sciences, which are generally taught to medical students in their first year at medical school. Human anatomy can be taught regionally or systemically; that is, respectively, studying anatomy by bodily regions such as the head and chest, or studying by specific systems, such as the nervous or respiratory systems. The major anatomy textbook, [[Gray's Anatomy]], has been reorganized from a systems format to a regional format, in line with modern teaching methods. A thorough working knowledge of anatomy is required by physicians, especially [[surgery|surgeons]] and doctors working in some diagnostic specialties, such as [[histopathology]] and [[radiology]]. Academic anatomists are usually employed by universities, medical schools or teaching hospitals. They are often involved in teaching anatomy, and research into certain systems, organs, tissues or cells. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Invertebrate anatomy"
]
| [[Invertebrate]] constitute a vast array of living organisms ranging from the simplest unicellular [[eukaryote]] such as ''[[Paramecium]]'' to such complex multicellular animals as the [[octopus]], [[lobster]] and [[dragonfly]]. They constitute about 95% of the animal species. By definition, none of these creatures has a backbone. The cells of single-cell [[protozoa]] have the same basic structure as those of multicellular animals but some parts are specialized into the equivalent of tissues and organs. Locomotion is often provided by [[Cilium|cilia]] or [[Flagellum|flagella]] or may proceed via the advance of [[pseudopodia]], food may be gathered by [[phagocytosis]], energy needs may be supplied by [[photosynthesis]] and the cell may be supported by an [[endoskeleton]] or an [[exoskeleton]]. Some protozoans can form multicellular colonies. [[Metazoa]] are a multicellular organism, with different groups of cells serving different functions. The most basic types of metazoan tissues are epithelium and connective tissue, both of which are present in nearly all invertebrates. The outer surface of the epidermis is normally formed of epithelial cells and secretes an [[extracellular matrix]] which provides support to the organism. An endoskeleton derived from the [[mesoderm]] is present in [[echinoderm]], [[sponge]] and some [[cephalopod]]. [[Exoskeleton]] are derived from the epidermis and is composed of [[chitin]] in [[arthropod]] (insects, spiders, ticks, shrimps, crabs, lobsters). [[Calcium carbonate]] constitutes the shells of [[Mollusca|molluscs]], [[brachiopod]] and some tube-building [[Polychaete|polychaete worms]] and [[silica]] forms the exoskeleton of the microscopic [[diatom]] and [[radiolaria]]. Other invertebrates may have no rigid structures but the epidermis may secrete a variety of surface coatings such as the [[pinacoderm]] of sponges, the gelatinous cuticle of cnidarians ([[polyp (zoology)|polyp]], [[sea anemone]], [[jellyfish]]) and the [[collagen]] cuticle of [[annelid]]. The outer epithelial layer may include cells of several types including sensory cells, gland cells and stinging cells. There may also be protrusions such as [[Microvillus|microvilli]], cilia, bristles, [[Spine (zoology)|spines]] and [[tubercle]]. [[Marcello Malpighi]], the father of microscopical anatomy, discovered that plants had tubules similar to those he saw in insects like the silk worm. He observed that when a ring-like portion of bark was removed on a trunk a swelling occurred in the tissues above the ring, and he unmistakably interpreted this as growth stimulated by food coming down from the leaves, and being captured above the ring. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Invertebrate anatomy",
"Arthropod anatomy"
]
| [[Arthropod]] comprise the largest phylum in the animal kingdom with over a million known invertebrate species. [[Insect]] possess [[segmentation (biology)|segmented]] bodies supported by a hard-jointed outer covering, the [[exoskeleton]], made mostly of chitin. The segments of the body are organized into three distinct parts, a head, a [[Thorax (insect anatomy)|thorax]] and an [[abdomen]]. The head typically bears a pair of sensory [[Antenna (biology)|antennae]], a pair of [[compound eye]], one to three simple eyes ([[ocelli]]) and three sets of modified appendages that form the [[insect mouthparts|mouthparts]]. The thorax has three pairs of segmented [[arthropod leg|legs]], one pair each for the three segments that compose the thorax and one or two pairs of [[insect wing|wings]]. The abdomen is composed of eleven segments, some of which may be fused and houses the [[digestion|digestive]], [[Respiration (physiology)|respiratory]], [[Excretion|excretory]] and reproductive systems. There is considerable variation between species and many adaptations to the body parts, especially wings, legs, antennae and mouthparts. [[Spider]] a class of [[arachnid]] have four pairs of legs; a body of two segments—a [[cephalothorax]] and an [[abdomen]]. Spiders have no wings and no antennae. They have mouthparts called [[chelicerae]] which are often connected to venom glands as most spiders are venomous. They have a second pair of appendages called [[pedipalp]] attached to the cephalothorax. These have similar segmentation to the legs and function as taste and smell organs. At the end of each male pedipalp is a spoon-shaped cymbium that acts to support the [[palpal bulb|copulatory organ]]. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"Other branches of anatomy"
]
| (-) [[Superficial anatomy|Superficial or surface anatomy]] is important as the study of anatomical landmarks that can be readily seen from the exterior contours of the body. It enables physicians or [[veterinary surgeon]] to gauge the position and anatomy of the associated deeper structures. Superficial is a directional term that indicates that structures are located relatively close to the surface of the body. (-) [[Comparative anatomy]] relates to the comparison of anatomical structures (both gross and microscopic) in different animals. (-) Artistic anatomy relates to anatomic studies for artistic reasons. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
[
"History",
"Ancient"
]
| In 1600 BCE, the [[Edwin Smith Papyrus]], an [[Ancient Egyptian medicine|Ancient Egyptian]] [[Medical manual|medical text]], described the [[heart]], its vessels, [[liver]], [[spleen]], [[kidneys]], [[hypothalamus]], [[uterus]] and [[Urinary bladder|bladder]], and showed the [[blood vessel]] diverging from the heart. The [[Ebers Papyrus]] (c. 1550 BCE) features a "treatise on the heart", with vessels carrying all the body's fluids to or from every member of the body. Ancient Greek anatomy and physiology underwent great changes and advances throughout the early medieval world. Over time, this medical practice expanded by a continually developing understanding of the functions of organs and structures in the body. Phenomenal anatomical observations of the human body were made, which have contributed towards the understanding of the brain, eye, liver, reproductive organs and the nervous system. The [[Hellenistic Egypt]] city of [[Alexandria]] was the stepping-stone for Greek anatomy and physiology. Alexandria not only housed the biggest library for medical records and books of the liberal arts in the world during the time of the Greeks, but was also home to many medical practitioners and philosophers. Great patronage of the arts and sciences from the [[Ptolemy]] rulers helped raise Alexandria up, further rivalling the cultural and scientific achievements of other Greek states. | 674 | Anatomy | [
"Anatomy",
"Anatomical terminology",
"Branches of biology",
"Morphology (biology)"
]
| [
"Plastination",
"Outline of human anatomy",
"Anatomical model"
]
|
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