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Since this number increases down the group, the atomic radius must also increase down the group.
The 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.
First ionisation energy
The first ionisation energy of an element or molecule is the energy required to move the most loosely held electron from one 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 by the inner electrons and the distance from the most loosely held electron from the nucleus, which is always an oute |
r electron in main group elements. 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 stabilisation and contraction of the 7s orbital, bringing francium's valence electron closer to the nucleus than would be expected from nonrelativistic 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 secondmost loosely held electron is part of a fully filled e |
lectron shell and is thus difficult to remove.
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 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 reactions, 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 radius and thus the metallic bond must increase in length, making the 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.
Electronegativity
Electronegativity is a chemical property that describes the tendency of an atom or a functional group to attract electrons or electron density towards itself. If the bond between sodium and chlorine in sodium chloride were 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 le |
ss 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 Li I will dissolve in organic solvents, a property of most covalent compounds. Lithium fluoride LiF is the only alkali halide that is not soluble in water, and lithium hydroxide LiOH is the only alkali metal hydroxide that is not deliquescent.
Melting and boiling points
The melting point of a substance is the point where it changes state from solid to liquid while the boiling point of a substance in liquid state is the point where the 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 bonds keeping the atoms in place weaken so that the atoms can move around, and the metallic bonds eventually break co |
mpletely 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.
Density
The alkali metals all have the same crystal structure bodycentred 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.
Compounds
The alkali metals form complete series of compounds with all usually encountered anions, whi |
ch 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 bonding gives way to metallic bonding along the series NaCl, Na2O, Na2S, Na3P, Na3As, Na3Sb, Na3Bi, Na.
Hydroxides
All the alkali metals react vigorously or explosively with cold water, producing an aqueous solution of a strongly 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 the |
re 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 attr |
action 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 oligomeric alkoxides. They easily react with carbon dioxide to form carbonates or bicarbonates, or with hydrogen sulfide to form sulfides or bisulfides, and may be used to separate thiols from petroleum. They react with amphoteric oxides for example, the oxides of aluminium, zinc, tin, and 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.
Intermetallic compounds
The alkali metals form many intermetallic compounds with each other and the elements from groups 2 to 13 in the periodic table |
of varying stoichiometries, such as the sodium amalgams with mercury, including Na5Hg8 and Na3Hg. 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 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.
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 conductors or semiconductors, unlike the normal alloys with the preceding elements, implying that the alkali metal involved has lost an electron to the 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 Tln 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 borides tend to be boronrich, involving appreciable boronboron bonding involving 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 dec |
reases 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 LiB10, NaB6, NaB15, and KB6. Under high pressure the boronboron bonding in the lithium borides changes from following Wade's rules to forming Zintl anions like the rest of group 13.
Compounds with the group 14 elements
Lithium and sodium react with carbon to form acetylides, Li2C2 and Na2C2, which can also be obtained by reaction of the metal with acetylene. Potassium, rubidium, and caesium react with graphite; their atoms are intercalated between the hexagonal graphite layers, forming graphite intercalation compounds of formulae MC60 dark grey, almost black, MC48 dark grey, almost black, MC36 blue, MC24 steel blue, and MC8 bronze M K, Rb, or Cs. These compounds are over 200 times more electrically conductive than pure graphit |
e, suggesting that the valence electron of the alkali metal is transferred to the graphite layers e.g. . Upon heating of KC8, the elimination of potassium atoms results in the conversion in sequence to KC24, KC36, KC48 and finally KC60. KC8 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 MC8, the smaller ones initially form MC6, 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 MnC60; 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 cagelike structures are formed, such as the silicides M4Si4 M K, Rb |
, or Cs, which contains M and tetrahedral ions. The chemistry of alkali metal germanides, involving the germanide ion Ge4 and other cluster Zintl ions such as , , , and Ge926, is largely analogous to that of the corresponding silicides. Alkali metal stannides are mostly ionic, sometimes with the stannide ion Sn4, and sometimes with more complex Zintl ions such as , which appears in tetrapotassium nonastannide K4Sn9. The monatomic plumbide ion Pb4 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.
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 unreactive gas because breaking the strong triple bond in the dini |
trogen molecule N2 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 N2 and the formation of N3 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 Na3N and potassium nitride K3N, while existing, are extremely unstable, being prone to decomposing back into their constituent elements, and cannot be produc |
ed 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 M3Pn 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 P3 and As3 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 K3P, K4P3, K5P4, KP, K4P6, K3P7, K3P11, KP10.3, and KP15. While most metals form arsenides, only the alkali and alkaline earth metals form mostly ionic arsenides. The structur |
e of Na3As is complex with unusually short NaNa distances of 328330 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 M3As are known, such as LiAs, which has a metallic lustre and electrical conductivity indicating the presence of some metallic bonding. The antimonides are unstable and reactive as the Sb3 ion is a strong reducing agent; reaction of them with acids form the toxic and unstable gas stibine SbH3. Indeed, they have some metallic properties, and the alkali metal antimonides of stoichiometry MSb involve antimony atoms bonded in a spiral Zintl structure. Bismuthides are not even wholly ionic; they are intermetallic compounds containing partially metallic and partially ionic bonds.
Oxides and chalcogenides
All the alkali metals react vigorously with oxygen at standard conditions. They form various types of oxides, such as simple oxides con |
taining the O2 ion, peroxides containing the ion, where there is a single bond between the two oxygen atoms, superoxides 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, a |
llowing 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 O2 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 agents. 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 vap |
our, 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 ozonides MO3 through lowtemperature 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 M2O3, 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 Rb6O and Rb9O2 coppercoloured upon oxidation in air, while caesium forms an immense variety of oxides, such as the ozonide CsO3 and several brightly coloured suboxides, such as Cs7O bronze, Cs4O redviolet, Cs11O3 violet, Cs3O dark green, CsO, Cs3O2, as well as Cs7O2. The last of these may be heated under |
vacuum to generate Cs2O.
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 Na2S and various polysulfides with the formula Na2Sx x from 2 to 6, containing the ions. Due to the basicity of the Se2 and Te2 ions, the alkali metal selenides and 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, watersoluble compounds that air oxidises quickly back to selenium or tellurium. The alkali |
metal polonides are all ionic compounds containing the Po2 ion; they are very chemically stable and can be produced by direct reaction of the elements at around 300400 C.
Halides, hydrides, and pseudohalides
The alkali metals are among the most electropositive elements on the periodic table and thus tend to bond ionically to the most electronegative elements on the periodic table, the halogens fluorine, chlorine, bromine, iodine, and astatine, forming 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 wellknown 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 me |
lting points. All the alkali metal halides are 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 interactions 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 pseudohalide these are often used as reducing agents, producing hydrides, complex metal hydrides, or hydrogen gas. Other pseudohalides are also known, notably the cyanides. 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 Na3ClO, K3BrO yellow, Na4Br2O, Na4I2O, and K4Br2O, are also known. The polyhalides are rather unstable, alth |
ough those of rubidium and caesium are greatly stabilised by the feeble polarising power of these extremely large cations.
Coordination complexes
Alkali metal cations do not usually form coordination complexes with simple Lewis bases 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 numbers from 1 to 12, although octahedral hexacoordination is its preferred mode. In aqueous solution, the alkali metal ions exist as octahedral hexahydrate complexes MH2O6, with the exception of the lithium ion, which due to its small size forms tetrahedral tetrahydrate complexes LiH2O4; 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 cati |
ons are often used as desiccants. Alkali metals also readily form complexes with crown ethers e.g. 12crown4 for Li, 15crown5 for Na, 18crown6 for K, and 21crown7 for Rb and cryptands due to electrostatic attraction.
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 alkali metal amide MNH2, 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 metals calcium, strontium, barium, as well as the divalent lanthanides, 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 electrons, 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 coppercoloured and has approximately the conductivity of liquid metals like 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 alkali metal molecules M2 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 agents and are often used in chemical synthesis.
Organometallic
Organolithium
Being the smallest alkali metal, lithium forms the widest variety of and most stable organometallic compounds, which are bonded covalently. Organolithium compounds are electrically nonconducting volatile solids or liquids that melt at low temperatures, an |
d tend to form oligomers with the structure RLix 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 bases and nucleophiles. For use as bases, butyllithiums are often used and are commercially available. An example of an organolithium compound is methyllithium CH3Lix, which exists in tetrameric x 4, tetrahedral and hexameric x 6, octahedral forms. Organolithium compounds, especially nbutyllithium, 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 aldehydes and ketones by reaction with metal carbonyls. 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 NiCO4 LiRCONiCO3
LiRCONiCO3 Li RCHO solventNiCO3
LiRCONiCO3 Li R'COR solventNiCO3
Alkyllithiums and aryllithiums may also react with N,Ndisubstituted amides to give aldehydes and ketones, and symmetrical ketones by reacting with carbon monoxide. They thermally decompose to eliminate a hydrogen, producing alkenes and lithium hydride another route is the reaction of ethers with alkyl and aryllithiums that act as strong bases. In nonpolar solvents, aryllithiums react as the carbanions they effectively are, turning carbon dioxide to aromatic carboxylic acids ArCO2H and aryl ketones to tertiary carbinols Ar'2CArOH. Finally, they may be used to synthesise other organometallic compounds through metalhalogen exchange.
Heavier alkali metals
Unlike the organolithium compounds, the organometallic compounds of the heavier alkali metals are predominantly ionic. The application of organosodium compounds in che |
mistry is limited in part due to competition from organolithium compounds, 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 nbutyllithium and potassium tertbutoxide. This reagent reacts with propene to form the compound allylpotassium KCH2CHCH2. cis2Butene and trans2butene 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 sterically congested conformation. Several crystal structures of organopotassium compounds have been reported, establishing that th |
ey, 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 ethers, 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 RR' MX
As such, they have to be made by reacting 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 cyclopentadienes and terminal alkynes, to give salts. Liquid ammonia, ether, or hydrocarbon solvents are used, the most common of which being tet |
rahydrofuran. The most important of these compounds is sodium cyclopentadienide, NaC5H5, an important precursor to many transition metal cyclopentadienyl derivatives. Similarly, the alkali metals react with cyclooctatetraene in tetrahydrofuran to give alkali metal cyclooctatetraenides; for example, dipotassium cyclooctatetraenide K2C8H8 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 darkgreen sodium naphthalenide, NaC10H8, a strong reducing agent.
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 a |
re unstable in water. The peroxide anion is weakly bound to the cation, and it is hydrolysed, forming stronger covalent bonds.
Na2O2 2H2O 2NaOH H2O2
The other oxygen compounds are also unstable in water.
2KO2 2H2O 2KOH H2O2 O2
Li2O H2O 2LiOH
Reaction with sulfur
With sulfur, they form sulfides and polysulfides.
2Na 18S8 Na2S 18S8 Na2S2...Na2S7
Because alkali metal sulfides are essentially salts of a weak acid and a strong base, they form basic solutions.
S2 H2O HS HO
HS H2O H2S HO
Reaction with nitrogen
Lithium is the only metal that combines directly with nitrogen at room temperature.
3Li 13N2 Li3N
Li3N can react with water to liberate ammonia.
Li3N 3H2O 3LiOH NH3
Reaction with hydrogen
With hydrogen, alkali metals form saline hydrides that hydrolyse in water.
Na H2 NaH at high temperatures
NaH H2O NaOH H2
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 Li2C2
Na C2H2 NaC2H 12H2 at 1500C
Na NaC2H Na2C2 at 2200C
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 H2O NaOH 12H2
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 4000C van Arkelde Boer process.
TiCl4 4Na 4NaCl Ti
Reaction with organohalide compounds
Alkali metals react with halogen derivatives to generate hydrocarbon via the Wurtz reaction.
2CH3Cl 2Na H3CCH3 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 xNH3 Na eNH3x
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
S8 2e S82
FeCO5 2e FeCO42 CO
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 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 is due to the relativistic |
stabilisation of ununennium's valence electron, increasing ununennium's first ionisation energy and decreasing the metallic and 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 pm, very close to that of rubidium 247 pm, so tha |
t 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 porbitals 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 7p32 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 7p32 electrons in the bonding.
Not as much work has been done predicting the properties of the alkali metals beyond ununennium. Although a simple extrapolat |
ion of the periodic table by the aufbau principle would put element 169, unhexennium, under ununennium, DiracFock calculations predict that the next element after ununennium with alkalimetallike properties may be element 165, unhexpentium, which is predicted to have the electron configuration Og 5g18 6f14 7d10 8s2 8p122 9s1. 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 state |
s beyond 1, whence the likely transition metal behaviour of unhexpentium. Due to the alkali and alkaline earth metals both being sblock 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 6g1, it returns to the alkalimetallike situation of having one easily removed electron far above a closed pshell 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 shellstructure effects become so strong that extrapolations from lighter congeners become completely inaccurate. In addition, the relativistic and shellstructure effe |
cts which stabilise the sorbitals and destabilise and expand the d, f, and gorbitals of higher shells have opposite effects, causing even larger difference between relativistic and nonrelativistic 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 islands of stability, centered at elements 122 306Ubb and 164 482Uhq.
Pseudoalkali metals
Many other substances are similar to the alkali metals in their tendency to form monopositive cations. Analogously to the pseudohalogens, they have sometimes been called "pseudoalkali metals". These substances include some elements and many more polyatomic ions; the polyatomic ions are especially similar to the alkali metals in their large size and weak polarising power.
Hydrogen
The element hydrogen, with one electron per neutral atom, is usually placed at the top of Group 1 of the periodic tabl |
e 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 H2; however, the alkali metals form diatomic molecules such as dilithium, Li2 only at high temperatures, when they are in the gaseous state.
Hydrogen, like the alkali metals, has one valence electron and reacts easily with the halogens, 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 kJmol 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 alkalides, 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 pressures, 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 electrical resistivity of liquid m |
etallic 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 nonmetaltometal transition.
The 1s1 electron configuration of hydrogen, while analogous to that of the alkali metals ns1, is unique because there is no 1p subshell. Hence it can lose an electron to form the 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 acidbase |
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 fm compared to the 50220 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 acidbase chemistry. Also unique is hydrogen's ability to form hydrogen bonds, which are an effect of chargetransfer, 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.
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 salts are 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 GPa, and could possibly occur inside the 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 "pseudoalkali 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 cations are very useful since they are permanently charged, and they are often us |
ed 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 pnictogens, 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.
Cobaltocene and derivatives
Cobaltocene, CoC5H52, 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 18electron rule. This additional electron occupies an orbital that is antibonding with respect to the CoC bonds. Consequently, many chemical reactions of CoC5H52 are |
characterized by its tendency to lose this "extra" electron, yielding a very stable 18electron 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 wellstudied due to its instability.
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 stabilisation of the 6s orbital and the decreasing bond energy as the atoms increase in size so that the amount of energy release |
d 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 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 stereochemically active in aqueous solution. Additionally, the thallium halides except TlF are quite insoluble in water, and TlI has an unusual structure because of the presence of the stereochemically active inert pair in thallium.
Copper, silver, and gold
The group 11 metals or coinage metals, copper, silver, and gold, are typically categorised as transition metals given they can form ions with incomplete dshells. Physically, they have the relatively low melting points and high electronegativity values associated with posttransition metals. "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 t |
hat lower electron mobility." Chemically, the group 11 metals behave like maingroup 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 posttransition 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 metals, 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 copperII and goldIII compounds being known at that time. However, elimin |
ating group IB would make group I the only main group group VIII was labelled a transition group to lack an AB 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 mediumlong 18column periodic table, which separated the alkali metals and group 11 metals.
The coinage metals were traditionally regarded as a subdivision of the alkali metal group, due to them sharing the characteristic s1 electron configuration of the alkali metals group 1 p6s1; group 11 d10s1. However, the similarities are largely confined to the 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 correspo |
nding 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 5d106s1 configuration has one electron less than the quasiclosed shell 5d106s2 configuration of mercury.
Production and isolation
The pro |
duction 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 aluminiumIII ions from the ore leaching, whereupon basic precipitation removes aluminium ions from the mixture by precipitating it as the 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, are 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 springs, 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.
Metals like sodium are obtained by electrolysi |
s of molten salts. Rb Cs obtained mainly as by products of Li processing. To make pure cesium, ores of cesium and rubidium are crushed and heated to 650 C with sodium metal, generating an alloy that can then be separated via a fractional distillation technique. Because metallic cesium is too reactive to handle, it is normally offered as cesium azide CsN3. Cesium hydroxide is formed when cesium interacts aggressively with water and ice CsOH.
Rubidium is the 16th most prevalent element in the earth's crust, however it is quite rare. Some minerals found in North America, South Africa, Russia, and Canada contain rubidium. Some potassium minerals lepidolites, biotites, feldspar, carnallite contain it, together with caesium. Pollucite, carnallite, leucite, and lepidolite are all minerals that contain rubidium. As a byproduct of lithium extraction, it is commercially obtained from lepidolite. Rubidium is also found in potassium rocks and brines, which is a commercial supply. The majority of rubidium is now obtaine |
d as a byproduct of refining lithium. Rubidium is used in vacuum tubes as a getter, a material that combines with and removes trace gases from vacuum tubes.
For several years in the 1950s and 1960s, a byproduct 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 byproduct from pollucite. Today, a common method for separating rubidium from potassium and caesium is the fractional crystallisation of a rubidium and caesium alum Cs, RbAlSO4212H2O, 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 tonnes 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, e |
xtracted from the ore mainly by three methods acid digestion, alkaline decomposition, and direct reduction. Both metals are produced as byproducts 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 197Au 18O 210Fr 5 n, yielding francium209, francium210, and francium211. 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 francium223 is specifically required, it is produced as the alpha daughter of actinium227, itself produced synthetically from the neutron irradiation of natural radium226, one of the daughters of natural uranium238.
Applica |
tions
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 lithiumion 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 wellknown being sodium chloride as table salt. Sodium salts of fatty acids are used as soap. Pure sodium metal also has many applications, including use in sodiumvapour 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 ma |
ny other metals, such as titanium and zirconium, from their chlorides. Furthermore, it is very useful as a heatexchange liquid in fast breeder nuclear reactors due to its low melting point, viscosity, and crosssection towards neutron absorption.
Potassium compounds are often used as fertilisers 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 clocks. 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 year |
s. For that reason, caesium atoms are used as the definition of the second. Rubidium ions are often used in purple fireworks, 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 levels and the coupling constants between subatomic particles. Studies on the light emitted by lasertrapped francium210 ions have provided accurate data on transitions between atomic energy levels, similar to those predicted by quantum theory.
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, halocarbons, plastics, 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 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 oxygencontaining atmosphere for longer than 6 months.
Ions
The bioinorganic chemistry of the alkali metal ions has been extensively reviewed.
Solid state crystal structures have been det |
ermined 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 manicdepression in daily doses of about 0.5 to 2 grams, although there are sideeffects. Excessive ingestion of lithium causes drowsiness, slurred speech and vomiting, among other symptoms, and poisons 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 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 functio |
ning as electrolytes inside and outside 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; 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 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 potentiala "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.
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 potassium deficiency. Partial substitution is quite possible and rather nontoxic a 70 kg person contains on average 0.36 g of rubidium, and an increase in this valu |
e 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 |
50 value for caesium chloride in mice is 2.3 g per kilogram, which is comparable to the LD50 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.
Radioisotopes of caesium require special precautions the improper handling of caesium137 gamma ray sources can lead to release of this radioisotope and radiation injuries. Perhaps the bestknown case is the Goinia accident of 1987, in which an improperlydisposedof radiation therapy system from an abandoned clinic in the city of Goinia, Brazil, was scavenged from a junkyard, and the glowing caesium salt sold to curious, uneducated buyers. This led to four deaths and serious injuries from radiation exposure. Together with caesium134, iodine131, and strontium90, caesium137 was among the isotopes distributed by the Chernobyl disaster which constitute the greatest risk to hea |
lth. Radioisotopes of francium would presumably be dangerous as well due to their high decay energy and short halflife, but none have been produced in large enough amounts to pose any serious risk.
Notes
References
A
Groups periodic table
Periodic table
Articles containing video clips |
An alphabet is a standardized set of basic written symbols or graphemes called letters that represent the phonemes of certain spoken languages. Not all writing systems represent language in this way; in a syllabary, each character represents a syllable, for instance, and logographic systems use characters to represent words, morphemes, or other semantic units.
The first fully phonemic script, the ProtoCanaanite script, later known as the Phoenician alphabet, is considered to be the first alphabet, and is the ancestor of most modern alphabets, including Arabic, Cyrillic, Greek, Hebrew, Latin, and possibly Brahmic. It was created by Semiticspeaking workers and slaves in the Sinai Peninsula as the ProtoSinaitic script, by selecting a small number of hieroglyphs commonly seen in their Egyptian surroundings to describe the sounds, as opposed to the semantic values, of their own Canaanite language. However, Peter T. Daniels distinguishes an abugida, or alphasyllabary, a set of graphemes that represent consonantal |
base letters which diacritics 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 or Arabic, and an "alphabet", a set of graphemes that represent both consonants and vowels. 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, and which is now used by many languages worldwide, often with the addition of extra letters or diacritical marks. While most alphabets have letters composed of lines linear writing, there are also exceptions such as the alphabets used in Braille. The Khmer alphabet for Khmer 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 lists and number placements.
Etymology
The English word alphabet came into Middle English from the Late Latin word alphabetum, which in turn originated in the Greek alphabtos. The Greek word was made from the first two letters, alpha and beta . The names for the Greek letters came from the first two letters of the Phoenician alphabet; aleph, which also meant ox, and 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.
History
Ancient Northeast African and Middle Eastern scripts
The history of the alphabet started in ancient Egypt. Egyptian writing had a set of some 24 hieroglyphs that are called uniliterals, to represent syllab |
les 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 logograms, 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 ProtoSinaitic 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 elHol 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 syllabar |
y, 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 ProtoSinaitic script eventually developed into the Phoenician alphabet, which is conventionally called "ProtoCanaanite" 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 and Aramaic. The Aramaic gave rise to the 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 abjads, currently exemplified in scripts including Arabic, Hebrew, and 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 matres lectionis. These letters have a dual function since they are also used as pure consonants.
The ProtoSinaitic or ProtoCanaanite 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.
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 soun |
ds 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 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.
European alphabets
The Greek alphabet, in its 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 western and central Europe.
Some adaptations of the Latin alphabet are augmented with ligatures, such as in Dani |
sh and Icelandic and in Algonquian; by borrowings from other alphabets, such as the thorn in Old English and Icelandic, which came from the Futhark runes; and by modifying existing letters, such as the eth 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, 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 alphabets. Elder Futhark gave rise to a variety of alphabets known collectively as the Runic alphabets. 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, Macedonian, Bulgarian, Russian, Belarusian and 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 Greek and Hebrew.
The longest European alphabet is the Latinderived Slovak alphabet, which has 46 letters. |
Asian alphabets
Beyond the logographic Chinese writing, many phonetic scripts are in existence in Asia. The Arabic alphabet, Hebrew alphabet, Syriac alphabet, and other abjads 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 mixedscript writing one syllable always takes up one typespace no matter how many letters get stacked into building that one soundblock.
Zhuyin sometimes called Bopomofo is a semisyllaba |
ry used to phonetically transcribe Mandarin Chinese in the Republic of China. After the later establishment of the People's Republic of China and its adoption of 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 initials are represented by individual symbols, but like a syllabary the phonemes of the syllable finals are not; rather, each possible final excluding the medial glide is represented by its own symbol. For example, luan is represented as luan, where the last symbol 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 systemthat is, for aiding in pronunciation and as an input method for Chinese characters on computers and cellphones.
Eu |
ropean 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 and Persian and sometimes as a complete alphabet as with Kurdish and Uyghur.
Types
The term "alphabet" is used by linguists and paleographers in both a wide and a narrow sense. In the wider sense, an alphabet is a script that is segmental at the phoneme levelthat 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, abjads and abugidas. 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 consonantbased, but indicate vowels with diacritics 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 lett |
ers. The earliest known alphabet in the wider sense is the Wadi elHol script, believed to be an abjad, which through its successor Phoenician is the ancestor of modern alphabets, including Arabic, Greek, Latin via the Old Italic alphabet, Cyrillic via the Greek alphabet and Hebrew via Aramaic.
Examples of presentday abjads are the Arabic and Hebrew scripts; true alphabets include Latin, Cyrillic, and Korean hangul; and abugidas are used to write Tigrinya, Amharic, Hindi, and 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 consonantvowel combination would be represented by a separate glyph.
All three types may be augmented with syllabic glyphs. 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 , , ; Coptic has a letter for . Devanagari is typically an abugida augmented with dedicated letters for initial vowels, though some traditions use as a zero consonant as the graphic base for such vowels.
The boundaries between the three types of segmental scripts are not always clearcut. For example, Sorani 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 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 Tigrinya abugida and the Amharic abugida ironi |
cally, 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 logographic. See below.
Thus the primary classification of alphabets reflects how they treat vowels. For 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 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 a true alphabet and Thai an abugida. In Thai, tone is determined primarily by the choice of consonant, with diacritics for disambiguation. In the Pol |
lard 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 and 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.
The number of letters in an alphabet can be quite small. The Book 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 okina and five long vowels. However, Hawaiian Braille has only 13 letters. While Rotokas has a small alphabet because it has few pho |
nemes to represent just eleven, Book Pahlavi was small because many letters had been conflatedthat is, the graphic distinctions had been lost over time, and diacritics were not developed to compensate for this as they were in Arabic, another script that lost many of its distinct letter shapes. For example, a commashaped letter represented g, d, y, k, or j. However, such apparent simplifications can perversely make a script more complicated. In later Pahlavi 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 wholethat is, they had become logograms as in 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 k and j, 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, with 51 letters. The largest alphabets in the narrow sense include Kabardian and Abkhaz for Cyrillic, with 58 and 56 letters, respectively, and Slovak for the Latin script, with 46. However, these scripts either count di and trigraphs as separate letters, as Spanish did with ch and ll until recently, or uses diacritics like Slovak .
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 Mesrop Matoc' 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 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 int |
o 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, o and f, were added in the Middle Ages. During the 1920s orthography reform, a new letter capital was added, which was a ligature before , while the letter was discarded and reintroduced as part of a new letter which was a digraph before.
The Armenian script's directionality is horizontal lefttoright, 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 ayb and ben.
Alphabetical order
Alphabets often come to be associated with a standard ordering of their letters, which can then be used for purposes of collationnamely for the listing o |
f 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 , , and and of certain combinations of letters multigraphs. In French, these are not considered to be additional letters for the purposes of collation. However, in Icelandic, the accented letters such as , , and are considered distinct letters representing different vowel sounds from the sounds represented by their unaccented counterparts. In Spanish, is considered a separate letter, but accented vowels such as and are not. The ll and ch were also considered single letters, but in 1994 the Real Academia Espaola 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 letterin contrast to several languages such as Albanian, in which dh, , 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 umlaut are collated ignoring the umlautcontrary to Turkish that adopted the graphemes and , and where a word like tfek, would come after tuz, in the dictionary. An exception is the German telephone directory where umlauts are sorted like ae since names such as Jger also appear with the spelling Jaeger, and are not distinguished in the spoken language.
The Danish and Norwegian alphabets end with , whereas the Swed |
ish and Finnish ones conventionally put at the end.
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 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, Greek, Armenian, Gothic, Cyrillic, and Latin; the other, HMLQ, was used in southern Arabia and is preserved today in Ethiopic. Both orders have therefore been stable for at least 3000 years.
Runic used an unrelated Futhark sequence, which was later simplified. 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.
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, Aramaic, Syriac, Hebrew, Greek and Arabic.
The names were abandoned in 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 Greekthis 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.
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 phonemes significant sounds of the spoken language. In a perfectly phonemic orthography there wo |
uld be a consistent onetoone 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 and 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 onetoone 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. Twoletter combinations are called digraph |
s and threeletter groups are called trigraphs. German uses the tetragraphs four letters "tsch" for the phoneme and in a few borrowed words "dsch" for . Kabardian also uses a tetragraph for one of its phonemes, namely "". Two letters representing one sound occur in several instances in Hungarian as well where, for instance, cs stands for t, sz for s, zs for , dzs for d.
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" 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 vocabulary.
National languages sometimes elect to address the problem of dialects by simply associating the alphabet with the national standard. Some national languages like Finnish, Armenian, Turkish, Russian, SerboCroatian Serbian, Croatian and Bosnian and Bulgarian have a very regular spelling system with a nearly onetoone 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 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, 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, with its silent letters and its heavy use of nasal vowels 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 Latinbased Turkish alphabet, and as when Kazakh changes from an Arabic script to a Cyrillic script due to the Soviet Union's influence, and in 2021, having a transition to the Latin alphabet, just like Turkish. The Cyrillic script used to be official in Uzbekistan and Turkmenistan before they all switched to the Latin alphabets, including Uzbekistan that is having a reform of the alphabet to use diacritics on the letters that is marked by apostrophes and the letters that are digraphs.
The standard system of symbols used by linguists to represent sounds in any language, independently of orthogr |
aphy, is called the International Phonetic Alphabet.
See also
A Is For Aardvark
Abecedarium
Acrophony
Akshara
Alphabet book
Alphabet effect
Alphabet song
Alphabetical order
Butterfly Alphabet
Character encoding
Constructed script
Cyrillic
English alphabet
Hangul
ICAO NATO spelling alphabet
Lipogram
List of writing systems
Pangram
Thai script
Thoth
Transliteration
Unicode
References
Bibliography
Overview of modern and some ancient writing systems.
Chapter 3 traces and summarizes the invention of alphabetic writing.
Chapter 4 traces the invention of writing
External links
The Origins of abc
"Language, Writing and Alphabet An Interview with Christophe Rico", Damqtum 3 2007
Michael Everson's Alphabets of Europe
Evolution of alphabets, animation by Prof. Robert Fradkin at the University of Maryland
How the Alphabet Was Born from HieroglyphsBiblical Archaeology Review
An Early Hellenic Alphabet
Museum of the Alphabet
The Alphabet, BBC Radio 4 discuss |
ion with Eleanor Robson, Alan Millard and Rosalind Thomas In Our Time, 18 Dec. 2003
Orthography |
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