Cesium (Cs) is a soft, silvery, ductile, metallic element produced as a by-product of zinc refining and by reduction of cesium chloride. It is found mainly as the mineral pollucite. Cesium is one of the alkali metals, found in Group I of the periodic table. It is the most electropositive and alkaline of elements, turns to a liquid at only 28.5°C, and burns spontaneously in moist air. It is used in photoelectric cells, as a catalyst promoter, and to make special glass. The radioisotope cesium-137 can be employed in radiotherapy, but is now rarely used. The cesium (atomic) clock provides the standard measure of time: the electron resonance frequency of the cesium atom is exactly 9,192,631,770 cycles per second. Cesium has also been used in ion propulsion.
|relative atomic mass||132.905|
|first ionization energy||376 kJ/mol|
|atomic radius||265 pm|
|ionic radius||167 pm|
|melting point||28.5°C (83.3°F)|
|boiling point||690°C (1,274°F)|