from Latin caesius 'bluish grey', for its spectral colours
Discovery
Robert Bunsen and Gustav Kirchhoff (1860)
First isolation
Carl Setterberg (1882)
Isotopes of caesium
v
e
Main isotopes[7]
Decay
abundance
half-life (t1/2)
mode
product
131Cs
synth
9.7 d
ε
131Xe
133Cs
100%
stable
134Cs
synth
2.0648 y
ε
134Xe
β−
134Ba
135Cs
trace
1.33×106 y
β−
135Ba
137Cs
synth
30.17 y[8]
β−
137Ba
Category: Caesium
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Caesium (IUPAC spelling;[9]cesium in American English)[note 1] 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 28.5 °C (83.3 °F; 301.6 K), which makes it one of only five elemental metals that are liquid at or near room temperature.[note 2] Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoric and reacts with water even at −116 °C (−177 °F). It is the least electronegative 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 picometers.
The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in 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.
Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids, but it has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Nonradioactive caesium compounds are only mildly toxic, but the pure metal's tendency to react explosively with water means that caesium is considered a hazardous material, and the radioisotopes present a significant health and environmental hazard.
^"Standard Atomic Weights: Caesium". CIAAW. 2013.
^Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^ abcArblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
^Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.121. ISBN 1-4398-5511-0.
^Dye, J. L. (1979). "Compounds of Alkali Metal Anions". Angewandte Chemie International Edition. 18 (8): 587–598. doi:10.1002/anie.197905871.
^"Magnetic susceptibility of the elements and inorganic compounds". Handbook of Chemistry and Physics(PDF) (87th ed.). CRC press. ISBN 0-8493-0487-3. Retrieved 26 September 2010.
^Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^"NIST Radionuclide Half-Life Measurements". NIST. Retrieved 13 March 2011.
^"IUPAC Periodic Table of Elements". International Union of Pure and Applied Chemistry.
^International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. pp. 248–49. Electronic version..
^Coghill, Anne M.; Garson, Lorrin R., eds. (2006). The ACS Style Guide: Effective Communication of Scientific Information (3rd ed.). Washington, D.C.: American Chemical Society. p. 127. ISBN 978-0-8412-3999-9.
^Coplen, T. B.; Peiser, H. S. (1998). "History of the recommended atomic-weight values from 1882 to 1997: a comparison of differences from current values to the estimated uncertainties of earlier values" (PDF). Pure Appl. Chem. 70 (1): 237–257. doi:10.1351/pac199870010237. S2CID 96729044. Archived (PDF) from the original on 21 May 2011.
^OED entry for "caesium". Second edition, 1989; online version June 2012. Retrieved 7 September 2012. Earlier version first published in New English Dictionary, 1888.
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Caesium (IUPAC spelling; cesium in American English) is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali...
Caesium (55Cs) has 41 known isotopes, the atomic masses of these isotopes range from 112 to 152. Only one isotope, 133Cs, is stable. The longest-lived...
The caesium standard is a primary frequency standard in which the photon absorption by transitions between the two hyperfine ground states of caesium-133...
22 minutes. It is the second-most electropositive element, behind only caesium, and is the second rarest naturally occurring element (after astatine)...
fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770...
Caesium chloride or cesium chloride is the inorganic compound with the formula CsCl. This colorless salt is an important source of caesium ions in a variety...
chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1...
Caesium heptafluoroxenate is an inorganic compound of caesium, and fluorine, and xenon with the chemical formula CsXeF7. Caesium heptafluoroxenate can...
the caesium frequency, Δ ν Cs {\displaystyle \Delta \nu _{\text{Cs}}} , the unperturbed ground-state hyperfine transition frequency of the caesium-133...
Caesium zirconate is an inorganic compound of caesium, oxygen, and zirconium with the chemical formula Cs2ZrO3. Caesium zirconate can be prepared from...
Caesium iodide or cesium iodide (chemical formula CsI) is the ionic compound of caesium and iodine. It is often used as the input phosphor of an X-ray...
of caesium are known. Caesium oxide may refer to: Caesium suboxides (Cs7O, Cs4O, and Cs11O3) Caesium monoxide (Cs2O, the most common oxide) Caesium peroxide...
Caesium fluoride or cesium fluoride is an inorganic compound with the formula CsF. A hygroscopic white salt, caesium fluoride is used in the synthesis...
Caesium bicarbonate or cesium bicarbonate is a chemical compound with the chemical formula CsHCO3. It can be produced through the following reaction:...
Caesium hydroxide is a strong base (pKa= 15.76) containing the highly reactive alkali metal caesium, much like the other alkali metal hydroxides such...
2018. Radioactive particles from the incident, including iodine-131 and caesium-134/137, have since been detected at atmospheric radionuclide sampling...
whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher...
Caesium carbonate or cesium carbonate is a chemical compound with the chemical formula Cs2CO3. It is white crystalline solid. Caesium carbonate has a...
Allium caesium, light blue garlic, is a species of herbaceous perennial flowering plant native to central Asia (Xinjiang, Kazakhstan, Kyrgyzstan, Tajikistan...
Caesium permanganate is the permanganate salt of caesium, with the chemical formula CsMnO4. Caesium permanganate can be formed by the reaction of potassium...
Caesium selenide is an inorganic compound of caesium and selenium. It is a selenide, with the chemical formula of Cs2Se. It can be prepared by reacting...
structure is the "interpenetrating primitive cubic" structure, also called a "caesium chloride" or B2 structure. This structure is often confused for a body-centered...
Caesium acetate or cesium acetate is an ionic caesium compound with the molecular formula CH3COOCs. It is a white solid that may be formed by the reaction...
Caesium superoxide is a chemical compound with the chemical formula CsO2. It consists of caesium cations Cs+ and superoxide anions O−2. It is an orange...
Caesium nitrate or cesium nitrate is a salt with the chemical formula CsNO3. An alkali metal nitrate, it is used in pyrotechnic compositions, as a colorant...
Caesium monoxide or caesium oxide is an chemical compound with the chemical formula Cs2O. It is the simplest and most common oxide of the caesium. It...