Electronic data		Thermal data		Steric data
Shells: 2,8,18,18,8,1 Orbitals: [Xe] 6s1 Electronegativity: 0.9, 0.7 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 () Covalent radius: 2.35 Å Atomic volume: 71.07 cm³/mol Density (293 K): 1.873 g/cm³ Crystal structure: Cubic: Body centered

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Nuclide	Abundance [%]	Mass	Spin	Halflife	Decay mode	Decay tree
126Cs	0	126	1	1.64m	+,EC	View
129Cs	0	129	1/2	1.336d	EC,+	View
131Cs	0	131	5/2	9.69d	EC	View
132Cs	0	132	2	6.48d	EC,+,-	View
133Cs	100	133.905	7/2	--	stable	--
134Cs	0	134	4	2.065y	-,EC	View
134Csm	0	134	8	2.91h	IT	View
135Cs	0	135	7/2	2.3E06y	-	View
136Cs	0	136	5	13.16d	-	View
137Cs	0	137	7/2	30.17y	-,b-	View
138Cs	0	138	3	32.2m	-	View
139Cs	0	139	7/2	9.3m	-	View

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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.