Caesium (Cs)

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Cesium 55Cs132.905

Discovered in 1860 by R. Bunsen und G.R. Kirchhoff at Heidelberg, Germany.

[Latin, caesius = sky bluw]

French: césium
German: Caesium
Italian: cesio
Spanish: cesio

Description: Caesium/Cesium (US) is a soft, shiny, gold-coloured metal which oxidises repidly in air and reacts explosively with water. It is obtained by the electrolysis of molten caesium cyanide, and by other methods. Caesiumand its salts are used commercially as catalyst promoters, in special glasses, and in radiation monitoring equipment.


Further Materials properties


Crystal structure: (cell dimensions/pm), space group, 
b.c.c. (78 K) (a=614), Im3m
High pressure forms: (a= 598.4), Fm3m; (a=580.0), Fm3m
X-ray diffractions mass absorption coefficients: CuKa 318 (µ/r) / cm2g-1
MoKa 41.3 (µ/r) / cm2g-1
Neutron scattering length: 0.542 b/10-12 cm
Thermal neutron capture cross-section: 29 sa / barns
Density: 1873 kg/m-3 [293 K]; 1843[liquid at m.p.]
Melting point: 28.4°C / 301,55°K
Boiling point: 678.45°C / 951.6°K
Molar volume: 70.96 cm3
Thermal conductivity: 35.9 [300 K] W m-1K-1
Coefficient of linear thermal expansion: 97 x 10-6 K-1
Electrical resistivity: 20.0 x 10-8 [293 K] Ωm
Mass magnetic susceptibility: +2.8 x 10-8(s) kg-1m3
Young's modulus: 1.7 GPa
Rigidity modulus: 0.65 GPa
Bulk modulus: n.a.
Poisson's ratio: 0.295 GPa
Radi: Cs+ 165; atomic 265.4; covalent 235; van der Waals 262
Electronegativity: 0.79 (Pauling); 0.86 (Allred); 2.18 eV (absolute)
Effective nuclear charge: 2.20 (Slater); 6.36 (Clementi); 8.56 (Froese-Fischer)
Number of Isotopes (incl. nuclear isomers): 40
Isotope mass range: 114 -> 145



Biological data


Biological role: No known biological role, but it may partly replace potassium
Toxic intake: n.a. but regarded as fairly toxic
Lethal intake: LD50 (Cs2CO3, oral, rat) = 2333 mg Kg-1
Hazards: Although similar to potassium, caesium can have serious effects on the body if taken in excess. Rats fed Cs in place of K died after two weeks. 134Cs and 137Cs are dangerous radioactive pollutants which have escaped from nuclear reactors.
Level in humans  
Blood: 0.0038 mg dm-3
Bone: 0.013 - 0.052 ppm
Liver: 0.04 - 0.05 ppm
Muscle: 0.07 - 1.6 ppm
Daily dietary intake: 0.004 - 0.03 mg
Total mass of element in average
[70 kg] person:
c. 6 mg


Geological data


Minerals:Few are known
MineralFormulaDensityHardnessCrystal apperance
Cesium kupleskite  Cs3(Mn,Fe)7(Ti,Nb)2Si8O24.(OH,F)7  3.68  4  tric., dull gold-brown
Pollucite  (Cs,Na)2Al2Si4O12.nH2O  2.94  6.5  cub., col., vit.

Chief ores: pollucite; cesium is also found in lepidolite (see lithium)
World production: c. 20 (cesium compounds) tonnes/year
Main mining areas: Bernic Lake (Manitoba, Canada), Bikita (Zimbabwe) and South-West Africa
Reserves: c. 100 000 (60 000 at Bernic Lake)
Specimen: available as small ingots in sealed ampoules. Danger!


Sun: <80 (relative to H = 1 x 1012)
Earth's crust: 3 ppm
Seawater 3.0 x 10-4
Residence time: 600 000 years
Classification: accumulating
Oxidation state: I

  Source: Emsley, J. (1998) The Elements (3rd Edition)

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Overview of elements with access to our shop

1 18
2 13 14 15 16 17
Li Be B C
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se
Rb Sr Y Zr Nb Mo
Ru Rh Pd Ag Cd In Sn Sb Te I
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Ce Pr Nd
Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

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