Caesium is a soft metal which is often liquid at room temperature due to its relatively low melting point (28.5C). It is an extremely reactive metal, reacting violently in contact with water and being rapidly attacked in air. As with other alkaline group metals, caesium can be prepared by electrolysis of the fused halides but, in addition, it can also be prepared by heating the chloride with calcium and distilling out the molten metal. As a photosensitor, caesium has a peak response at 800nm in the infrared, both thermal- and photo-emission being high. Alloys of caesium with antimony, gallium, indium and thorium are generally photosensitive. Caesium is also used in atomic clocks, a standard measure of time, based on the caesium ion resonance of 9,192,631,770 Hz.


1860 by R. Bunsen and G. R. Kirchoff in Heidelberg, Germany.

7 ppm of Earth's crust.

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Atomic number 55 Clip
Atomic / Molecular Weight 132.9054 gmol-1Clip
Density 1900 kgm-3Clip
Crystal Structure bcc Clip
Lattice constant 614 fmClip
Melting Point 301.56 KClip
Boiling Point 959 KClip
Specific heat capacity 234 Jkg-1K-1Clip
Thermal conductivity 36 Wm-1K-1Clip
Bulk Modulus of Rigidity 1600000000 Nm-2Clip
Electromotive Series 3.02 VClip
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See also: Bunsen, Robert Wilhelm, Caesium Bromide, Caesium Chloride, Caesium Fluoride, Caesium Hydride, Caesium Iodide, Caesium Oxide, Caesium Peroxide, Caesium Sulphide, Caesium Superoxide, Periodic Table.

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Subjects: Chemistry