Alkali metal

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Alkali metals in the periodic table
Hydrogen (other non-metal)
 
Helium (noble gas)
Lithium (alkali metal)
Beryllium (alkaline earth metal)
 
Boron (metalloid)
Carbon (other non-metal)
Nitrogen (other non-metal)
Oxygen (other non-metal)
Fluorine (halogen)
Neon (noble gas)
Sodium (alkali metal)
Magnesium (alkaline earth metal)
 
Aluminium (post-transition metal)
Silicon (metalloid)
Phosphorus (other non-metal)
Sulfur (other non-metal)
Chlorine (halogen)
Argon (noble gas)
Potassium (alkali metal)
Calcium (alkaline earth metal)
 
Scandium (transition metal)
Titanium (transition metal)
Vanadium (transition metal)
Chromium (transition metal)
Manganese (transition metal)
Iron (transition metal)
Cobalt (transition metal)
Nickel (transition metal)
Copper (transition metal)
Zinc (transition metal)
Gallium (post-transition metal)
Germanium (metalloid)
Arsenic (metalloid)
Selenium (other non-metal)
Bromine (halogen)
Krypton (noble gas)
Rubidium (alkali metal)
Strontium (alkaline earth metal)
   
Yttrium (transition metal)
Zirconium (transition metal)
Niobium (transition metal)
Molybdenum (transition metal)
Technetium (transition metal)
Ruthenium (transition metal)
Rhodium (transition metal)
Palladium (transition metal)
Silver (transition metal)
Cadmium (transition metal)
Indium (post-transition metal)
Tin (post-transition metal)
Antimony (metalloid)
Tellurium (metalloid)
Iodine (halogen)
Xenon (noble gas)
Caesium (alkali metal)
Barium (alkaline earth metal)
Lanthanum (lanthanoid)
Cerium (lanthanoid)
Praseodymium (lanthanoid)
Neodymium (lanthanoid)
Promethium (lanthanoid)
Samarium (lanthanoid)
Europium (lanthanoid)
Gadolinium (lanthanoid)
Terbium (lanthanoid)
Dysprosium (lanthanoid)
Holmium (lanthanoid)
Erbium (lanthanoid)
Thulium (lanthanoid)
Ytterbium (lanthanoid)
Lutetium (lanthanoid)
Hafnium (transition metal)
Tantalum (transition metal)
Tungsten (transition metal)
Rhenium (transition metal)
Osmium (transition metal)
Iridium (transition metal)
Platinum (transition metal)
Gold (transition metal)
Mercury (transition metal)
Thallium (post-transition metal)
Lead (post-transition metal)
Bismuth (post-transition metal)
Polonium (post-transition metal)
Astatine (halogen)
Radon (noble gas)
Francium (alkali metal)
Radium (alkaline earth metal)
Actinium (actinoid)
Thorium (actinoid)
Protactinium (actinoid)
Uranium (actinoid)
Neptunium (actinoid)
Plutonium (actinoid)
Americium (actinoid)
Curium (actinoid)
Berkelium (actinoid)
Californium (actinoid)
Einsteinium (actinoid)
Fermium (actinoid)
Mendelevium (actinoid)
Nobelium (actinoid)
Lawrencium (actinoid)
Rutherfordium (transition metal)
Dubnium (transition metal)
Seaborgium (transition metal)
Bohrium (transition metal)
Hassium (transition metal)
Meitnerium (unknown chemical properties)
Darmstadtium (unknown chemical properties)
Roentgenium (unknown chemical properties)
Copernicium (transition metal)
Ununtrium (unknown chemical properties)
Flerovium (unknown chemical properties)
Ununpentium (unknown chemical properties)
Livermorium (unknown chemical properties)
Ununseptium (unknown chemical properties)
Ununoctium (unknown chemical properties)
↓ Period
2 Lithium metal stored under paraffin
3
Li
3 Sodium metal
11
Na
4 Potassium metal
19
K
5 Rubidium metal in a glass ampoule
37
Rb
6 Caesium metal in a glass ampoule
55
Cs
7 87
Fr

Legend

Alkali metal
Primordial
From decay

The alkali metals are a group of chemical elements in the periodic table with very similar properties: they are all shiny, soft, silvery, highly reactive metals at standard temperature and pressure[1] and readily lose their outermost electron to form cations with charge +1.[2]:28 They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to oxidation.[1] Because of their high reactivity, they must be stored under oil in sealed glass ampoules to prevent reaction with air.[3] In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements,[note 1] excluding hydrogen (H), which is nominally a group 1 element[5][6] but not normally considered to be an alkali metal[7][8] as it rarely exhibits behaviour comparable to that of the alkali metals.[9] All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones.[1][10]

The alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).[5] This group lies in the s-block of the periodic table[11] as all alkali metals have their outermost electron in an s-orbital.[1][12][13] The alkali metals provide the best example of group trends in properties in the periodic table,[1] with elements exhibiting well-characterized homologous behaviour.[1]

All the discovered alkali metals occur in nature.[14][15] Experiments have been conducted to attempt the synthesis of ununennium (Uue), which is likely to be the next member of the group, but they have all met with failure.[16] However, ununennium may not be an alkali metal due to relativistic effects, which are predicted to have a large influence on the chemical properties of superheavy elements.[17]

Most alkali metals have many different applications. Two of the most well-known applications of the pure elements are rubidium and caesium atomic clocks,[18] of which caesium atomic clocks are the most accurate representation of time known as of 2012.[19][20] A common application of the compounds of sodium is the sodium-vapour lamp, which emits very efficient light.[21][22] Table salt, or sodium chloride, has been used since antiquity

Chemical Properties

Series of alkali metals, stored in mineral oil to prevent oxidation. (“Natrium” is sodium.)

Like other groups, the members of this family show patterns in its electronic configuration, especially the outermost shells, resulting in trends in chemical behavior:

Z Element No. of electrons/shell Electron configuration[note 2]
3 lithium 2, 1 [He] 2s1
11 sodium 2, 8, 1 [Ne] 3s1
19 potassium 2, 8, 8, 1 [Ar] 4s1
37 rubidium 2, 8, 18, 8, 1 [Kr] 5s1
55 caesium 2, 8, 18, 18, 8, 1 [Xe] 6s1
87 francium 2, 8, 18, 32, 18, 8, 1 [Rn] 7s1
119 ununennium 2, 8, 18, 32, 32, 18, 8, 1 (predicted)[23]:1722 [Uuo] 8s1 (predicted)[23]:1722

Most of the chemistry has been observed only for the first five members of the group. The chemistry of francium is not well established due to its radioactivity,[1] and ununennium has not yet been discovered; thus, the presentation of their properties here is limited. All the alkali metals are highly reactive and are never found in elemental forms in nature.[24] Because of this, they are usually stored in mineral oil or kerosene (paraffin oil).[3]

 
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Caesium reacts explosively with water even at low temperatures

The alkali metals are all silver-coloured except for metallic caesium, which can have a golden tint.[25] All are soft and have low densities,[1] melting points,[1] and boiling points.[1] In chemical terms, all of the alkali metals react aggressively with the halogens to form the alkali metal halides, which are white ionic crystalline compounds that are all soluble in water except lithium fluoride (LiF).[1] The alkali metals also react with water to form strongly alkaline hydroxides and thus should be handled with great care. The heavier alkali metals react more vigorously than the lighter ones; for example, when dropped into water, caesium produces a larger explosion than potassium.[1][10][19] The alkali metals have the lowest first ionisation energies in their respective periods of the periodic table[13] because of their low effective nuclear charge[1] and the ability to attain a noble gas configuration by losing just one electron. The second ionisation energy of all of the alkali metals is very high[1][13] as it is in a full shell that is also closer to the nucleus;[1] thus, they almost always lose a single electron, forming cations.[2]:28 The alkalides are a major exception: they have alkali metals in a −1 oxidation state, which is very unusual as before the discovery of the alkalides, the alkali metals were not expected to be able to form anions and were thought to be able to appear in salts only as cations. The alkalide anions have filled s-subshells. All the stable alkali metals except lithium are known to be able to form alkalides,[26][27][28] and the alkalides have much theoretical interest due to their unusual stoichiometry and low ionisation potentials. Alkalides are chemically similar to the electrides, which are salts with trapped electrons acting as anions.[29] A particularly striking example of an alkalide is “inverse sodium hydride“, H+Na, as opposed to the usual sodium hydride, Na+H.[30]

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