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An element in the alkali metal group. Cesium has an abundance of 1 ppm in the earth's crust. It occurs in the minerals pollucite and lepidolite. Cesium was discovered in 1860 by Robert Bunsen and Gustav Kirchhoff. It is a soft, silvery white metal that tarnishes on contact with air and can ignite spontaneously in moist air. Cesium is used as a catalyst for polymers and as a radioactive emitter in atomic clocks. It is also used in photoelectric sensors for security devices and cameras.

Synonyms and Related Terms

Cs; caesium (IUPAC); cesium (US,. Ned., Sven.); césium (Fr.); Cäsium (Deut.); cesio (It., Esp.); Césio (Port.)

Other Properties

Flame color is blue to purple. Violently decomposes in water with the evolution of hydrogen. Soluble in liquid ammonia.

Composition Cs (atomic no. 55)
CAS 7440-46-2
Mohs Hardness 0.2
Melting Point 28.5
Density 1.873
Molecular Weight atomic wt. =132.9054
Boiling Point 705

Hazards and Safety

Metallic cesium can ignite spontaneously in moist air. Dangerous fire and explosion risk. Reacts violently with oxidizing materials. Burns skin.

Fisher Scientific: MSDS

Additional Information

Web Elements: Website

Sources Checked for Data in Record

  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 180
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 2051
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998

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