(So named (
Latin caesius, "bluish-gray") in
1860 by
Robert Wilhelm Bunsen because of the blue line in its
spectrum) A soft, silver-white,
ductile,
metallic chemical element, one of the
alkali metals and the most
electropositive of all the
elements. It
ignites in
air, reacts vigorously with
water, and is used in
photoelectric cells.
Symbol: Cs
Atomic number: 55
Atomic weight: 132.91
Density (at room temperature and pressure): 1.873 g/cc
Melting point: 28.44°C
Boiling point: 671°C
Valence: +1
Ground state electron configuration: [Xe]6s1
See also: cesium-137