Template:Infobox caesium

Caesium,  ₅₅Cs

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General properties
Pronunciation	Template:Infobox element/pronunciation
Alternative name	cesium (US, informal)
Appearance	pale gold
Standard atomic weight (Ar, standard)	Template:Infobox element/standard atomic weight
Mass number	Template:Infobox element/symbol-to-most-stable-isotope (most stable isotope)
Caesium in the periodic table
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Atomic number (Z)	55
Group	Template:Infobox element/group
Period	period 6
Block	s-block
Element category	Template:Infobox element/category format
Electron configuration	[Xe] 6s1
Electrons per shell	2, 8, 18, 18, 8, 1
Physical properties
Phase at STP	solid
Melting point	301.7 K ​(28.5 °C, ​83.3 °F)
Boiling point	944 K ​(671 °C, ​1240 °F)
Density (near r.t.)	1.93 g/cm3
when liquid (at m.p.)	1.843 g/cm3
Critical point	1938 K, 9.4 MPa
Heat of fusion	2.09 kJ/mol
[[Enthalpy of vaporization|Heat of Template:Engvar]]	63.9 kJ/mol
Molar heat capacity	32.210 J/(mol·K)
[[Vapor pressure|Template:Engvar pressure]] Template:Infobox element/vapor pressure table
Atomic properties
Oxidation states	Template:Infobox element/symbol-to-oxidation-state
Electronegativity	Pauling scale: 0.79
[[Ionization energy|Template:Engvar energies]]	1st: 375.7 kJ/mol 2nd: 2234.3 kJ/mol 3rd: 3400 kJ/mol
Atomic radius	empirical: 265 pm
Covalent radius	244±11 pm
Van der Waals radius	343 pm
Template:Infobox element/spectral lines
Other properties
Crystal structure	​Template:Infobox element/crystal structure Template:Infobox element/crystal structure
Thermal expansion	97 µm/(m·K) (at 25 °C)
Thermal conductivity	35.9 W/(m·K)
Electrical resistivity	205 nΩ·m (at 20 °C)
Magnetic ordering	paramagnetic
Young's modulus	1.7 GPa
Bulk modulus	1.6 GPa
Mohs hardness	0.2
Brinell hardness	0.14 MPa
CAS Number	7440-46-2
History
Naming	from Latin caesius, sky blue, for its spectral colours
Discovery	Robert Bunsen and Gustav Kirchhoff (1860)
First isolation	Carl Setterberg (1882)
Main isotopes of caesium
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