caesium
Sign in to saveCaesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoric and reacts with water even at . It is the least electronegative stable element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from polluci
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Caesium is a soft, silvery-golden metal that is liquid at or near room temperature, making it one of only a few elemental metals with this unusual property. It is highly reactive with water and is the least electronegative stable element, which gives it distinctive chemical properties that make it useful for various applications.
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27 sectionsContents
- Spelling
- Characteristics
- Physical properties
- Allotropes
- Chemical properties
- Compounds
- Complexes
- Halides
- Oxides
- Isotopes
- Occurrence
- Production
- History
- Applications
- Petroleum exploration
- Atomic clocks
- Definition of the second
- Electric power and electronics
- Centrifugation fluids
- Chemical and medical use
- Nuclear and isotope applications
- Other uses
- Health and safety hazards
- See also
- Notes
- References
- External links
Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoric and reacts with water even at . It is the least electronegative stable element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite. Caesium-137, a fission product, is extracted from waste produced by nuclear reactors. It has the largest atomic radius of all elements whose radii have been measured or calculated, at about 260 picometres.
The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the then newly developed method of flame spectroscopy. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in the light-sensitive anodes of photoelectric cells. Caesium is widely used in highly accurate atomic clocks. In 1967, the International System of Units began using a specific hyperfine transition of neutral caesium-133 atoms to define the basic unit of time, the second.