Relative atomic mass: 132.9054519 +- 0.0000002

English: Caesium
French: Cesium
Croatian: Cezij
German: Caesium
Italian: Cesio
Spanish: Cesio

Atomic number: 55
Group numbers: 1
Period: 6
Standard state (20 oC): solid

Discovery: 1860 Robert Wilhelm Bunsen, Gustav Robert Kirchhoff (DE)
Caesium was discovered by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff (DE) in 1860. The origin of the name comes from the Latin word caesius meaning sky blue or heavenly blue. It is a very soft, light grey, ductile metal that reacts readily with oxygen and reacts explosively with water. Caesium is found in pollucite [(Cs4Al4Si9O26).H2O] and as trace in lepidolite. It is used as a 'getter' to remove air traces in vacuum and cathode-ray tubes, in producing photoelectric devices and atomic clocks. Since it ionises readily, it is used as an ion rocket motor propellant. The price of 99.8 % pure cesium metal is 461.80 for 50 g.
Electronic configuration: [Xe] 6s1
Formal oxidation number: +1
Atomic radius: 265.5 pm

Electronegativities: 0.79
Thermal conductivity: 35.9 W/(m K)
Electrical resistivity (20 oC): 20 microOhm cm

Melting point: 28.44 oC
Boiling point: 671 oC

Heat of fusion: 2.09 kJ/mol
Heat of vaporization: 66.5 kJ/mol
Heat of atomization: 77.58 kJ/mol

54Xe <= 55Cs => 56Ba

ASCII Periodic Table of the Elements
6 Jan. 2020
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