Caesium chloride


412.6 pm (at T = 298 K)

Cs, Cl

White, odorless solid


3.97 g · cm -3

646 ° C

1382 ° C

Very well in water (1860 g · l-1 at 20 ° C)


2004 mg · kg -1 ( LD50, rat, oral)

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Cesium chloride, a salt with the formula CsCl forms colorless, cubic crystals ( Caesiumchloridstruktur ) and can dissolve in water, acids and alkalis. The cesium cations and chloride anions are free to move in solution, and the mobility of cesium ion in water is relatively high because the cesium ion only has a relatively weakly bound hydration shell. Cesium chloride is hygroscopic.


Cesium chloride has a characteristic cubic crystal structure in which each of eight cesium ion and chloride ions, each chloride ion is surrounded by eight cesium ions: The cubic unit cell, for example, be selected so that the chloride ions are sitting at the eight corners of the cube. Then the cesium ion is exactly in the center of the cube. Alternatively, one can also select a unit cell in which the cesium ions are in the corner locations of the cube and the chloride ion in the center of the cell. The Caesiumchloridstruktur with the relatively high coordination number of eight is only formed when alkali metal halides, if the cation is relatively large, so that it can be surrounded by eight anions. Otherwise, the sodium chloride structure is formed. Also brass with zinc contents of around 50 % has at temperatures below 468 ° C, the Caesiumchloridstruktur.


The standard enthalpy of cesium chloride is ΔHf0 = -443 kJ / mol.


Cesium chloride is often used in laboratory processes for the purification of nucleic acids or viruses by means of an ultracentrifuge. Here, after several hours of a density gradient ultracentrifugation forms itself off. The particles then accumulate according to their density in characteristic bands in the centrifuge tube and can be removed separately.

In addition, it is used in atomic absorption spectrometry as Ionisationspuffer of easily ionizable metals.