| Potassium - K
CAS: 7440-09-7 Description:Very soft, silvery metal Classification: Alkali Metal Date of Discovery: 1807 Discoverer: Sir Humphrey Davy Name Origin: English, potash, "pot ashes" Symbol Origin: Latin kalium, Arabic qali, "alkali" |
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Atomic Number: 19
Number of Neutrons: 20 Atomic Mass: 39.0983(1) amu Melting Point: 63.28 °C Boiling Point: 759.0 °C Density (293 K): 0.862 g/cm3 Atomic volume: 45.46 cm3/mol Electrical resistivity: 0.139 10-e6/cm 
Thermal conductivity: 1.024 W/cmK Enthalpy of atomization: 89.54 kJ/mol Enthalpy of vaporization: 79.870 kJ/mol Enthalpy of fusion: 2.334 kJ/mol Specific heat capacity: 0.75 J/gK |
Energy levels: 2-8-8-1
Electron configuration: [Ar]4s1 Crystal Structure: Cubic body centered Atomic radius: 2.77 Å Covalent radius: 2.03 Å Oxidation States: +1 Electronegativity, Pauling: 0.82 Electron affinity: 0.50147 eV First ionization energy: 4.341 eV 2nd ionization energy: 31.625 eV 3rd ionization energy: 45.72 eV Polarizability: 43.4 10-24cm3 |
| Isotope | Natural Abundance | Atomic Mass | Half-life | Decay Mode | Spin |
| 35K | 34.98801 | 0.19 s |  +; +, p |
3/2+ | |
| 36K | 35.98129 | 0.342 s | + |
2+ | |
| 37K | 36.9733769 | 1.23 s | + |
3/2+ | |
| 38mK | 0.924 s | + |
0+ | ||
| 38K | 37.969080 | 7.63 m | + |
3+ | |
| 39K | 93.2581(44) | 38.9637069 | Stable | 3/2+ | |
| 40K | 0.117(1) | 39.9639987 | 1.26 x 109 y | -; +, EC |
4- |
| 41K | 6.7302(44) | 40.9618260 | Stable | 3/2 + | |
| 42K | 41.9624031 | 12.36 h | - |
2- | |
| 43K | 42.96072 | 22.3 h | - |
3/2+ | |
| 44K | 43.96156 | 22.1 m | - |
2- | |
| 45K | 44.96070 | 17.8 m | - |
3/2+ | |
| 46K | 45.96198 | 1.8 m | - |
2- | |
| 47K | 46.96168 | 17.5 s | - |
1/2+ | |
| 48K | 47.96551 | 6.8 s | - |
(2-) | |
| 49K | 48.96745 | 1.26 s | - |
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Discovered in 1807 by Davy, who obtained it from caustic potash (KOH); this was the first metal isolated by electrolysis. 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 1000 m 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. 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. 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). 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. 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. Seventeen isotopes of
potassium are known. Ordinary potassium is composed of three isotopes, one of
which is 40K (0.0117%), a radioactive isotope with a half-life of 1.28 x 109 years. The radioactivity presents no appreciable hazard. 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.
LINKS: Brog's Bear Facts About Potassium Arthritis As A Chronic Potassium Deficiency Lumen Foods: Potassium Sorbate Potassium Chronicles Timely Topic: Potassium, As Important as Sodium? Return
Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998. |
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