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Potassium (K)
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Potassium 19K39.098
Isolated in 1807 by Sir Humphry Davy at London, England.
[English, potash; Latin, kalium]
French: potassium
German: Kalium
Italian: potassio
Spanish: potasio
Description: Potassium is a soft white metal which is silvery when first cut but oxidizes repidly in air. It reacts violently with water. Potassium is obtained from the reaction of sodium metal with potassium chloride. The metal itself is little used, but potassium compounds are important in fertilizers, chemicals and glass.
Further Materials properties
| Crystal structure: |
(cell dimensions/pm), space group, |
|---|---|
| X-ray diffractions mass absorption coefficients: | CuKa 143 (µ/r) / cm2g-1 MoKa 15.8 (µ/r) / cm2g-1 |
| Neutron scattering length: | 0.367 b/10-12 cm |
| Thermal neutron capture cross-section: | 2.1 sa / barns |
| Density: | 862 kg/m-3 [293 K]; 828 [liquid at m.p.] |
| Melting point: | 63.65°C / 336.8°K |
| Boiling point: | 773.85°C / 1047°K |
| Molar volume: | 45.36 cm3 |
| Thermal conductivity: | 102.4 [300 K] W m-1K-1 |
| Coefficient of linear thermal expansion: | 83 x 10-6 K-1 |
| Electrical resistivity: | 6.15 x 10-8 [273 K] Ωm |
| Mass magnetic susceptibility: | +6.15 x 10-8(s) kg-1m3 |
| Radi: | K+ 133; atomic 227; covalent 203; van der Waals 231 |
| Electronegativity: | 0.82 (Pauling); 0.91 (Allred); 2.42 eV (absolute) |
| Effective nuclear charge: | 2.20 (Slater); 3.50 (Clementi); 4.58 (Froese-Fischer) |
| Number of Isotopes (incl. nuclear isomers): | 18 |
| Isotope mass range: | 35-> 51 |
Biological data
| Biological role: | Essential to all living things. |
|---|---|
| Toxicity | |
| Toxic intake: | KCl = c. 4g |
| Lethal intake: | LD50 (chloride, oral, rat) = 2600 mg Kg-1 |
| Hazards: | The toxicity of potassium compounds is almost always that of the anion, not of the K+. However, although KCl is often used as a nutrient or dietary supplement, there are rare cases of excess ingestion by humans proving fatal. |
| Level in humans | |
| Blood: | 16020 mg dm-3 |
| Bone: | 2100 ppm |
| Liver: | 16 000 ppm |
| Muscle: | 16 000 ppm |
| Daily dietary intake: | 1400 - 7400 mg |
| Total mass of element in average [70 kg] person: |
140 g |
Geological data
| Minerals: | Potassium occurs in many minerals. | |||
|---|---|---|---|---|
| Mineral | Formula | Density | Hardness | Crystal apperance |
| Alunite | KAl3(SO4)2(OH)6 | 2.69 | 3.5 - 4 | rhom., vit. white/grey |
| Carnallite | KCl.MgCl2.6H2O | 1.602 | 2.5 | orth., greasy colourless-red |
| Orthoclase* | KAlSi3O8 | 2.563 | 6 - 6.5 | mon., vit. colourless/ white |
| Sylvite | KCl | 1.993 | 2 | cub., vit. colourless/white |
* Mined on a large scale for porcelain, ceramics and glass
| Chief ores: | sylvite, carnallite, alunite |
|---|---|
| World production: | 200 (potassium metal); 51 x 106 (potassium salts) tonnes/year |
| Producing areas: | Germany, Spain, Canada, USA, Italy |
| Reserves: | vast, > 1 x 1010 tonnes |
| Specimen: | available as chunks (in mineral oil) or ingots (in ampoules). Warning! |
| Abundances | |
|---|---|
| Sun: | 1.45 x 105 (relative to H = 1 x 1012) |
| Earth's crust: | 21 000 ppm |
| Residence time: | 5 x 106 years |
| Classification: | accumulating |
| Oxidation state: | I |
Source: Emsley, J. (1998) The Elements (3rd Edition)
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