Feb 7 2003
Background
Potassium (K) was discovered in 1807 by Sir Humphrey Davy in London.
Abundance and Extraction
Potassium is a soft, silvery coloured metal, which like other members of the alkali group of metals, is extremely reactive.
As with other members of the group, Potassium can be prepared by electrolysis of the fused halide.
Potassium is one of the more common alkali metals, there being 26000 ppm in the earth's crust, the main source being potassium chloride.
Occurrence
Potassium does not occur naturally.
Applications
Potassium has limited use as the pure metal, although it can be used with sodium as a coolant in liquid metal reactors.
It is more commonly used as a salt; for example potassium bromide (KBr), which is used in photography, and potassium carbonate (K2CO3) which has applications in the areas of fluxes, pharmaceuticals and soaps. One of the most important uses of potassium salts is as fertilisers.
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Potassium salts are commonly used as fertilisers. Image credit: Jen Watson/Shutterstock
Potassium and the Human Body
Potassium is an essential element for all living beings and, on average, a human being contains approximately 140 gm, the majority of which is present in muscle tissue.
Key Properties
The key properties of Potassium are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
19 |
| Atomic radius - Goldschmidt ( nm ) |
0.238 |
| Atomic weight ( amu ) |
39.0983 |
| Crystal structure |
Body centred cubic |
| Electronic structure |
Ar 4s1 |
| Photo-electric work function ( eV ) |
2.2 |
| Thermal neutron absorption cross-section ( Barns ) |
1.8 |
| Valences shown |
1 |
| Ionisation potential |
No. |
eV |
| |
1 |
4.34 |
| |
2 |
31.6 |
| |
3 |
45.7 |
| |
4 |
60.9 |
| |
5 |
82.7 |
| |
6 |
100 |
| Natural Isotope Distribution |
Mass No. |
% |
| |
39 |
93.26 |
| |
40 |
0.01 |
| |
41 |
6.73 |
| Electrical Properties |
| Electrical resistivity @ 20 °C ( µOhm.cm ) |
6.8 |
| Temperature coefficient @ 0-100 °C ( K-1 ) |
0.0057 |
| Mechanical Properties |
| Material condition |
Polycrystalline @ -190 °C |
| Bulk modulus ( GPa ) |
3.1 |
| Hardness – Mohs |
0.5 |
| Poisson’s ratio |
0.35 |
| Tensile modulus ( GPa ) |
3.53 |
| Physical Properties |
| Boiling point (°C ) |
760 |
| Density @ 20 °C ( g.cm-3 ) |
0.86 |
| Melting point (°C ) |
63.25 |
| Thermal Properties |
| Coefficient of thermal expansion @ 0-100 °C ( x10-6 K-1 ) |
83 |
| Latent heat of evaporation ( J.g-1 ) |
2033 |
| Latent heat of fusion ( J g-1 ) |
61 |
| Specific heat @ 25 °C ( J.K-1.kg-1 ) |
753 |
| Thermal conductivity @ 0-100 °C ( W.m-1.K-1 ) |
102.5 |
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