Caesium

Caesium is a soft metal which is often liquid at room temperature due to its relatively low melting point (28.5°C). 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.

Symbol

Cs

Discovered

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

Abundance

7 ppm of Earth's crust.

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Atomic number	55		Clip
Atomic / Molecular Weight	132.9054	gmol-1	Clip
Density	1900	kgm-3	Clip
Crystal Structure	bcc		Clip
Lattice constant	614	fm	Clip
Melting Point	301.56	K	Clip
Boiling Point	959	K	Clip
Specific heat capacity	234	Jkg-1K-1	Clip
Thermal conductivity	36	Wm-1K-1	Clip
Bulk Modulus of Rigidity	1600000000	Nm-2	Clip
Electromotive Series	3.02	V	Clip

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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.