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| Atomic Number: | 19 | Atomic Symbol: | K | | Atomic Weight: | 39.098 | Electron Configuration: | 2-8-8-1 | | Shells: | 2,8,8,1 | Filling Orbital: | 4s1 | | Melting Point: | 63.65oC | Boiling Point: | 774oC | | Uses: | Fertilizers, glass, soap and explosives |
History(English, potash - pot ashes; L.. kalium, Arab qali, alkali)
Discovered in 1807 by Sir Humphrey Davy, who obtained it from caustic potash
(KOH); this was the first metal isolated by electrolysis.
SourcesThe metal is the seventh most abundant and makes up about 2.4%
by weight of the earth's crust. Most potassium minerals are insoluble and the
metal is obtained from them only with great difficulty.
Certain minerals, however, such as sylvite, carnallite, langbeinite, and
polyhalite are found in ancientlake and sea beds and form rather extensive
deposits from which potassium and its salts can readily be obtained. Potash is
mined in Germany, New Mexico, California, Utah, and elsewhere. Large deposits of
potash, found at a depth of some 3000 ft in Saskatchewan, promise to be
important in coming years.
Potassium is also found in the ocean, but is present only in relatively small
amounts, compared to sodium.
ProductionPotassium is never found free in nature, but is obtained by
electrolysis of the hydroxide, much in the same manner as prepared by Davy.
Thermal methods also are commonly used to produce potassium (such as by
reduction of potassium compounds with CaC2, C, Si, or Na).
UsesThe greatest demand for potash has been in its use for fertilizers.
Potassium is an essential constituent for plant growth and is found in most
soils.
An alloy of sodium and potassium (NaK) is used as a heat-transfer medium.
Many potassium salts are of utmost importance, including the hydroxide, nitrate,
carbonate, chloride, chlorate, bromide, iodide, cyanide, sulfate, chromate, and
dichromate.
Properties- It is one of the most reactive and electropositive of metals.
- Except for iridium, it is the lightest known metal.
- It is soft, easily cut with a knife, and is silvery in appearance
immediately after a fresh surface is exposed.
- It rapidly oxidizes in air and must be preserved in a mineral oil such as
kerosene.
- As with other metals of the alkali group, it decomposes in water with the
evolution of hydrogen.
- It catches fire spontaneously on water.
- Potassium and its salts impart a violet color to flames.
IsotopesSeventeen isotopes of potassium are known. Ordinary potassium
is composed of three isotopes, one of which is 40K (0.0118%), a radioactive
isotope with a half-life of 1.28 x 10^9 years.
HandlingThe radioactivity presents no appreciable hazard.
CostMetallic potassium is available commercially for about $40/lb in
small quantities.
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