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Cesium ( Cs )

Material Information

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General Description:  

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

Cesium 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. It is not a common element, its abundancy on Earth being 7 ppm.

As a photosensitor, cesium has a peak response at 800nm in the infrared, both thermal- and photo-emission being high. Alloys of cesium with antimony, gallium, indium and thorium are generally photosensitive. Cesium is also used in atomic clocks, a standard measure of time, based on the caesium ion resonance of 9,192,631,770 Hz.

   

Atomic Properties

Atomic number 55
Atomic radius - Goldschmidt ( nm ) 0.27
Atomic weight ( amu ) 133
Crystal structure Body centred cubic
Electronic structure Xe 6s1
Ionization potential No. eV
1 3.89
2 25.10
Natural isotope distribution Mass No. %
132.91 100
Photo-electric work function ( eV ) 2.14
Thermal neutron absorption cross-section ( Barns ) 29
Valences shown 1

Electrical Properties

Electrical resistivity @20C ( µOhmcm ) 20
Temperature coefficient @0-100C ( K-1 ) 0.0044

Mechanical Properties

Material condition Polycrystalline
Hardness - Mohs 0.2

Physical Properties

Boiling point ( C ) 705
Density @20C ( g cm-3 ) 1.90
Melting point ( C ) 28.5

Thermal Properties

Coefficient of thermal expansion @1-26C ( x10-6 K-1 ) 97
Latent heat of evaporation ( J g-1 ) 611
Latent heat of fusion ( J g-1 ) 15.78
Specific heat @25C ( J K-1 kg-1 ) 230
All information and technical data are given as a guide only. Although every effort has been made to ensure that the information is correct, no warranty is given as to its completeness or accuracy.

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