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Rubidium is a a metallic chemical element (symbol Rb) with an atomic number of 37.


Name, Symbol, Number rubidium, Rb, 37
Chemical series alkali metals
Group, Period, Block 1, 5, s
Appearance grey white
Standard atomic weight 85.4678(3) g·mol-1
Electrons per shell 2, 8, 18, 8, 1
Physical properties
Phase solid
Density (near r.t.) 1.532 g·cm-3
Liquid density at m.p. 1.46 g·cm-3
Melting point 312.46K
(39.31°C, 102.76°F)
Boiling point 961K
(688°C, 1270°F)
Critical point (extrapolated)
2093 K, 16 MPa
Heat of fusion 2.19 kJ·mol-1
Heat of vaporization 75.77 kJ·mol-1
Heat capacity (25°C) 31.060 J·mol-1·K-1
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 434 486 552 641 769 958
Atomic properties
Crystal structure cubic body centered
Oxidation states 1
(strongly basic oxide)
Electronegativity 0.82 (Pauling scale)
Ionization energies
1st: 403.0 kJ·mol-1
2nd: 2633 kJ·mol-1
3rd: 3860 kJ·mol-1
Atomic radius 235 pm
Atomic radius (calc.) 265 pm
Covalent radius 211 pm
Van der Waals radius 244 pm
Magnetic ordering no data
Electrical resistivity (20°C) 128 nΩ·m
Thermal conductivity (300K) 58.2 W·m-1·K-1
Speed of sound (thin rod) (20 °C) 1300 m/s
Young's modulus 2.4 GPa
Bulk modulus 2.5 GPa
Mohs hardness 0.3
Brinell hardness 0.216 MPa
CAS registry number 7440-17-7


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