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Caesium

Metalsolid
Symbol: Cs
Atomic number: 55
Atomic mass: 132.90543
Group: Alkali Metal
CAS-number: 7440-46-2

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Physical data

Electronic dataThermal dataSteric data
Shells: 2, 8, 18, 18, 8, 1
Orbitals: [Xe] 6s1
Electronegativity: 0.7, 0.9
1. Ionization potential: 3.8939 eV
2. Ionization potential: 25.10 eV
3. Ionization potential: -- eV
Oxidation states: 1
Electrical conductivity: 0.0489 10^6
Melting point: 28.4 °C
Boiling point: 669.3 °C
Specific heat: 0.24 J/gK
Heat of fusion: 2.092 kJ/mol
Heat of vaporization: 67.740 kJ/mol
Thermal conductivity: 0.359 W/cmK
Atomic radius: 3.34 Å
Ionic radius: 1.74 Å (+1)
Covalent radius: 2.35 Å
Atomic volume: 71.07 cm³/mol
Density (293 K): 1.873 g/cm³
Crystal structure: cubic body centered
cubic body centered

Isotopes

NuclideAbundance [%]MassSpinHalflifeDecay modeDecay tree
126Cs 0 126 1 1.64m β+, EC View
129Cs 0 129 1/2 1.336d EC, β+ View
131Cs 0 131 5/2 9.69d EC View
132Cs 0 132 2 6.48d EC, β+, β- View
133Cs 100 133.905 7/2 -- --
134Cs 0 134 4 2.065y β-, EC View
134Csm 0 134 8 2.91h IT View
135Cs 0 135 7/2 2.3E06y β- View
136Cs 0 136 5 13.16d β- View
137Cs 0 137 7/2 30.17y β-, β- View
138Cs 0 138 3 32.2m β- View
139Cs 0 139 7/2 9.3m β- View

Other info

Name origin:Latin: coesius (sky blue); for the blue lines of its spectrum.
Description:Very soft, light gray, ductile metal.
Discovered by:Gustov Kirchoff, Robert Bunsen
Year:1860
Place:Germany
Sources:Found in pollucite [(Cs4Al4Si9O26).H2O] and as trace in lepidolite.
Use(s):Used as a 'getter' to remove air traces in vacuum and cathode-ray tubes. Also used in producing photoelectric devices and atomic clocks. Since it ionizes readily, it is used as an ion rocket motor propellant.