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Atomic Number: 19
Atomic Symbol: K
Atomic Weight: 39.098
Electron Configuration: [Ar]4s1
History
(English, potash - pot ashes; L.. kalium, Arab qali, alkali)
Discovered in 1807 by Davy, who obtained it from caustic potash (KOH); this was
the first metal isolated by electrolysis.
Sources
The 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 ancient lake 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.
Production
Potassium 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).
Uses
The 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 lithium, 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.
Isotopes
Seventeen 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 109 years.
Handling
The radioactivity presents no appreciable hazard.
Sources: CRC Handbook of Chemistry and
Physics and the American Chemical Society.
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