Supplier Data - Rubidium (Rb) (Goodfellow)

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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