Feb 7 2003
Rubidium (Rb) is a soft and highly reactive member of the alkali group of metals. Rubidium is widely distributed throughout nature, but only occurs in small amounts (its abundance in the earth’s crust is 310 ppm), the main source being carnallite, the hydrated chloride of magnesium and potassium.
The metal is obtained by the electrolysis of the fused halide, although Rubidium can be obtained on a laboratory scale by heating the chloride with calcium metal and distilling out the metal. The metal ignites spontaneously in air and reacts violently with water and applications are limited.
Discovered in 1861 by R.W. Bunsen and G. Kirchoff in Heidelberg, Germany.
Key Properties
The key properties of Rubidium are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
37 |
| Atomic radius - Goldschmidt ( nm ) |
0.251 |
| Atomic weight ( amu ) |
85.4678 |
| Crystal structure |
Body centred cubic |
| Electronic structure |
Kr 5s1 |
| Photo-electric work function ( eV ) |
2.1 |
| Thermal neutron absorption cross-section ( Barns ) |
0.5 |
| Valences shown |
1, 2, 3, 4 |
| Ionisation Potential |
No. |
eV |
| |
1 |
4.18 |
| |
2 |
27.3 |
| |
3 |
40.0 |
| |
4 |
52.6 |
| |
5 |
71.0 |
| |
6 |
84.4 |
| Natural Isotope Distribution |
Mass No. |
% |
| |
85 |
72.17 |
| |
87 |
27.83 |
| Electrical Properties |
| Electrical resistivity @ 20 °C ( µOhm.cm ) |
12.1 |
| Temperature coefficient @ 0-100 °C ( K-1 ) |
0.0048 |
| Mechanical Properties |
| Material condition |
Polycrystalline |
| Bulk modulus ( GPa ) |
2.5 |
| Hardness – Mohs |
0.3 |
| Poisson’s ratio |
0.30 |
| Tensile modulus ( GPa ) |
2.35 |
| Physical Properties |
| Boiling point ( °C ) |
686 |
| Density @ 20 °C ( g.cm-3 ) |
1.532 |
| Melting point ( °C ) |
38.89 |
| Thermal Properties |
| Coefficient of thermal expansion @ 0-100 °C ( x10-6 K-1 ) |
9.0 |
| Latent heat of evaporation ( J.g-1 ) |
887 |
| Latent heat of fusion ( J.g-1 ) |
25.7 |
| Specific heat @ 25 °C ( J.K-1.kg-1 ) |
360 |
| Thermal conductivity @ 0-100 °C ( W.m-1.K-1 ) |
58.2 |
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