Template:Infobox caesium

Caesium,  ₅₅Cs

Spectral lines of caesium
General properties
Name, symbol	caesium, Cs
Appearance	silvery gold
Pronunciation	/ˈsiːziəm/ SEE-zee-əm
Alternative name	cesium
Caesium in the periodic table
Rb ↑ Cs ↓ Fr xenon ← caesium → barium
Atomic number (Z)	55
Group, block	group 1 (alkali metals), s-block
Period	period 6
Element category	alkali metal
Standard atomic weight (±) (Ar)	132.90545196(6)
Electron configuration	[Xe] 6s1
per shell	2, 8, 18, 18, 8, 1
Physical properties
Phase	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
Heat of vapourisation	63.9 kJ/mol
Molar heat capacity	32.210 J/(mol·K)
vapour pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 418 469 534 623 750 940
Atomic properties
Oxidation states	+1, −1 ​(a strongly basic oxide)
Electronegativity	Pauling scale: 0.79
Ionisation 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
Miscellanea
Crystal structure	​body-centered cubic (bcc)
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)
Most stable isotopes of caesium
iso NA half-life DM DE (MeV) DP 133Cs 100% – (SF) <34.753 134Cs syn 2.0648 y ε 1.229 134Xe β− 2.059 134Ba 135Cs trace 2.3×106 y β− 0.269 135Ba 137Cs trace 30.17 y β− 1.174 137Ba
Decay modes in parentheses are predicted, but have not yet been observed

References

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