Caesium compounds: caesium iodide

caesium symbol icon

The caesium in caesium iodide formally is in the oxidation state 1.

Crystal structure of caesium iodide

Caesium iodide

  • Formula as often written: CsI
  • Hill system formula: Cs1I1
  • CAS registry number: [7789-17-5]
  • Formula weight: 259.81
  • Class: iodide


  • caesium iodide
  • caesium(I) iodide
  • cesium iodide
  • cesium(I) iodide

Physical properties

  • Colour: white
  • Appearance: crystalline solid
  • Melting point: 626°C; 621°C
  • Boiling point: 1280°C
  • Density: 4510 kg m-3


Coming soon...

Element analysis

Element percentages for the elements in caesium iodide
Element %
Cs 51.15
I 48.85


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

CsOH(aq) + HI(aq) → CsI(aq) + H2O(l)

While not a normal route of preparation because of the expense, caesium metal reacts vigorously with all the halogens to form caesium halides. So, it burns with iodine, I2, to form caesium(I) iodide, CsI.

2Cs(s) + I2(s) → 2CsI(s)

Solid state structure

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

Crystal structure of caesium iodide

Isotope pattern

What follows is the calculated isotope pattern for the CsI unit with the most intense ion set to 100%.

Formula: Cs1I1

mass  %
260 100.0 __________________________________________________


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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caesium atomic number