Caesium chloride

  • Formula: CsCl
  • Hill system formula: Cl1Cs1
  • CAS registry number: [7647-17-8]
  • Formula weight: 168.358
  • Class: chloride
  • Colour: white
  • Appearance: crystalline solid
  • Melting point: 646°C
  • Boiling point: 1290°C; 1297°C
  • Density: 3988 kg m-3

The following are some synonyms of caesium chloride:

  • caesium chloride
  • caesium(I) chloride
  • cesium chloride
  • cesium(I) chloride

The oxidation number of caesium in caesium chloride is 1.


One way to make caesium chloride is to react the hydroxide with hydrochloric acid. The resulting salt can then be purified by recrystallization.

CsOH(aq) + HCl(aq) → CsCl(aq) + H2O(l)

Caesium(I) chloride can also be made by the neutralization of caesium(I) carbonate with hydrochloric acid. The resulting salt can then be purified by recrystallization.

Cs2(CO3)(aq) + 2HCl(aq) → 2CsCl(aq) + H2O(l) + CO2(g)

While not a normal route of preparation because of the expense, caesium metal reacts vigorously with all the halogens to form sodium halides. So, it burns with chlorine, Cl2, to form caesium(I) chloride, CsCl.

2Cs(s) + Cl2(g) → 2CsCl(s)

Solid state structure

  • Geometry of caesium: 8 coordinate: cubic
  • Prototypical structure: CsCl

Crystal structure of caesium chloride

Element analysis

The table shows element percentages for CsCl (caesium chloride).

Element %
Cl 21.06
Cs 78.94

Isotope pattern for CsCl

The chart below shows the calculated isotope pattern for the formula CsCl with the most intense ion set to 100%.


The data on these compounds pages are assembled and adapted from the primary literature and several other sources including the following.

  • R.T. Sanderson in Chemical Periodicity, Reinhold, New York, USA, 1960.
  • N.N. Greenwood and A. Earnshaw in Chemistry of the Elements, 2nd edition, Butterworth, UK, 1997.
  • F.A. Cotton, G. Wilkinson, C.A. Murillo, and M. Bochmann, in Advanced Inorganic Chemistry, John Wiley & Sons, 1999.
  • A.F. Trotman-Dickenson, (ed.) in Comprehensive Inorganic Chemistry, Pergamon, Oxford, UK, 1973.
  • R.W.G. Wyckoff, in Crystal Structures, volume 1, Interscience, John Wiley & Sons, 1963.
  • A.R.West in Basic solid state chemistry Chemistry, John Wiley & Sons, 1999.
  • A.F. Wells in Structural inorganic chemistry, 4th edition, Oxford, UK, 1975.
  • J.D.H. Donnay, (ed.) in Crystal data determinative tables, ACA monograph number 5, American Crystallographic Association, USA, 1963.
  • D.R. Lide, (ed.) in Chemical Rubber Company handbook of chemistry and physics, CRC Press, Boca Raton, Florida, USA, 77th edition, 1996.
  • J.W. Mellor in A comprehensive treatise on inorganic and theoretical chemistry, volumes 1-16, Longmans, London, UK, 1922-1937.
  • J.E. Macintyre (ed.) in Dictionary of inorganic compounds, volumes 1-3, Chapman & Hall, London, UK, 1992.

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