DENSITY : 1.873 g/cm 3

Cesium is an alkali metal that reacts explosively with water and melts just above room temperature. The word "cesium" is derived from caesium (Latin for "sky blue"). The name was chosen because of the blue lines observed by Robert Bunsen and Gustav Kirchhoff during their analysis of springwater with a spectroscope in 1860. Currently, cesium metal is generated via thermal decomposition of the azide, electrolysis of molten CsCN, or reduction of molten CsCl with calcium vapor followed by fractional distillation .

Like the other alkali metals, cesium is a soft, silvery metal, but it appears golden if it has been exposed to small amounts of oxygen. It is not found in its metallic state in nature; it is obtained as a byproduct of lithium processing of the mineral lepidolite. Its most significant ore is pollucite, and the world's largest pollucite deposit is found in Bernic Lake, Manitoba, Canada. Cesium's average crustal abundance is about 3 parts per million. Cesium is the most electropositive stable element and will ignite if exposed to air. Cesium burns blue in the flame test.

Both cesium and its compounds find practical uses. Cesium metal can be used as a getter to remove oxygen in phototubes. It is used in atomic clocks that are accurate to within five seconds per every three hundred years. (A second is defined as 9,192,631,770 oscillations of a Cs-133 atom.) CsI and CsF are used in scintillation counters to monitor ionizing radiation. CsCl is used to create density gradients for the separation and purification of DNA via ultracentrifugation.

SEE ALSO Alkali Metals ; Bunsen, Robert .

Nathan J. Barrows


Emsley, John (2001). Nature's Building Blocks: An A-Z Guide to the Elements. New York: Oxford University Press.

Greenwood, Norman N., and Earnshaw, A. (1997). Chemistry of the Elements , 2nd edition. Boston: Butterworth-Heinemann.

Lide, David R., ed. (2000). CRC Handbook of Chemistry & Physics , 81st edition. New York: CRC Press.

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