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, 
b.c.c. (a=533.4), Im3m

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.
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.
MineralFormulaDensityHardnessCrystal 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!


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)

Other sizes and specifications on request

Overview of elements with access to our shop

1 18
2 13 14 15 16 17
Li Be B C
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se
Rb Sr Y Zr Nb Mo
Ru Rh Pd Ag Cd In Sn Sb Te I
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Ce Pr Nd
Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

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