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'''Caesium''' (or '''cesium''') is the [[chemical element]] with the [[atomic number]] 55 on the [[periodic table]]. Its symbol is '''Cs'''.

'''Caesium''' (or '''cesium''') is the [[chemical element]] with the [[atomic number]] 55 on the [[periodic table]]. Its symbol is '''Cs'''.

Caesium is an [[alkali]] [[metal]]. Its [[melt]]ing point is low (28&nbsp;°C). It is extremely [[Reaction|react]]ive. Because of its high reactivity, it is a [[danger]]ous chemical. It may set itself on fire (ignite) in air. It [[Explosion|explode]]s on contact with water. It reacts more violently than the other [[alkali metal]]s with water. Because of this, caesium is stored in [[mineral oil]].<ref name=USGS>William C. Butterman ''et al'' 2004. {{cite web|url = http://pubs.usgs.gov/of/2004/1432/2004-1432.pdf|format = PDF|publisher = United States Geological Survey|accessdate = 2009-12-27|title = Mineral Commodity Profile: Cesium}}</ref>

Caesium is an [[alkali]] [[metal]]. Its [[melt]]ing point is low (28&nbsp;°C). It is extremely [[Reaction|react]]ive. Because of its high reactivity, it is a [[danger]]ous chemical. It may set itself on fire (ignite) in air. It [[Explosion|explode]]s on contact with water. It reacts more violently than the other [[alkali metal]]s with water. Because of this, caesium is stored in [[mineral oil]].<ref name=USGS>William C. Butterman ''et al'' 2004. {{cite web|url = http://pubs.usgs.gov/of/2004/1432/2004-1432.pdf|publisher = United States Geological Survey|accessdate = 2009-12-27|title = Mineral Commodity Profile: Cesium}}</ref>

Caesium is a rare element. Since there is little caesium on the [[Earth]], it is rather expensive. The human body does not need caesium. In large amounts, its [[chemical compound]]<nowiki/>s are mildly poisonous because it is close to [[potassium]], which the body does need.

Caesium is a rare element. Since there is little caesium on the [[Earth]], it is rather expensive. The human body does not need caesium. In large amounts, its [[chemical compound]]<nowiki/>s are mildly poisonous because it is close to [[potassium]], which the body does need.

== History ==

== History ==

Caesium was first described in 1861, by [[Gustav Robert Kirchhoff]] and [[Robert Wilhelm Bunsen]]. They were testing [[mineral water]], from [[Rhineland-Palatinate|Bad Dürkheim]]. After they separated [[calcium]], [[strontium]], [[magnesium]] and [[lithium]], they saw two lines in the "blue" range of the [[spectrum]]. Because of these lines, they concluded that in addition to the elements already found, there must be another unknown substance in the mineral water. They named this substance caesium, after the color [[blue]].<ref name="bunsen">G. Kirchhoff, R. Bunsen: ''Chemische Analyse durch Spectralbeobachtungen''. In: ''Annalen der Physik und Chemie''. 1861, 189, 7, S.&nbsp;337–381 ({{DOI|10.1002/andp.18611890702}}).</ref>

Caesium was first described in 1860, by [[Gustav Robert Kirchhoff]] and [[Robert Wilhelm Bunsen]]. They were testing [[mineral water]], from [[Rhineland-Palatinate|Bad Dürkheim]]. After they separated [[calcium]], [[strontium]], [[magnesium]] and [[lithium]], they saw two lines in the "blue" range of the [[spectrum]]. Because of these lines, they concluded that in addition to the elements already found, there must be another unknown substance in the mineral water. They named this substance caesium, after the color [[blue]].<ref name="bunsen">G. Kirchhoff, R. Bunsen: ''Chemische Analyse durch Spectralbeobachtungen''. In: ''Annalen der Physik und Chemie''. 1861, 189, 7, S.&nbsp;337–381 ({{doi|10.1002/andp.18611890702}}).</ref>

 

== Isotopes and compounds ==

== Isotopes and compounds ==

Caesium has at least 39 known isotopes ranging in atomic mass from 112 to 151. Only one of these, {{sup|133}}Cs, is stable. Therefore, the naturally-occurring [[isotope]] of caesium is {{sup|133}}Cs, which is not [[radioactive]]. {{sup|133}}Cs is used in [[atomic clock]]s, its vibration frequency used to define the length of the [[second]]. Another isotope, {{sup|137}}Cs is not made naturally but is made after [[nuclear fission]] has been done. It is very radioactive and used as an industrial [[gamma ray]] source.  

Caesium has at least 39 known isotopes ranging in atomic mass from 112 to 151. Only one of these, {{sup|133}}Cs, is stable. Therefore, the naturally-occurring [[isotope]] of caesium is {{sup|133}}Cs, which is not [[radioactive]]. {{sup|133}}Cs is used in [[atomic clock]]s, its vibration frequency used to define the length of the [[second]]. Another isotope, {{sup|137}}Cs is not made naturally but is made after [[nuclear fission]] has been done. It is very radioactive and used as an industrial [[gamma ray]] source.  

Caesium forms [[Chemical compound|compounds]] with many other [[chemical element]]s. Caesium formate is used in oil drilling because of its high [[density]].

Caesium forms [[Chemical compound|compounds]] with many other [[chemical element]]s. Caesium formate is used in oil drilling because of its high [[density]].

File:Rb&Cs crystals.jpg|Caesium crystals (golden) compared to [[rubidium]] crystals (silvery)

Caesium is extremely reactive in air and water. Caesium rapidly oxidizes in air and can spontaneously combust<ref>{{Cite web|url=https://www.compoundchem.com/2019/08/06/iypt055-caesium/|title=IYPT 2019 Elements 055: Caesium: Atomic clocks and explosive reactions|last=Interest|first=Compound|date=2019-08-06|website=Compound Interest|language=en-GB|access-date=2019-11-13}}</ref> (randomly catch on fire) at any moment. For this reason, it [http://www.chemistryexplained.com/elements/A-C/Cesium.html must be stored in] [[kerosene]] or a [[Oil|mineral oil,]] like other group one elements ([[Lithium]], [[Sodium|Natrium]], [[Rubidium]], and [[Francium]].) In water, Caesium violently reacts to make Caesium Hydroxide (2CsOH).<ref>{{Cite web|url=https://www.webelements.com/caesium/chemistry.html|title=WebElements Periodic Table » Caesium » reactions of elements|website=www.webelements.com|access-date=2019-11-13}}</ref>  The Caesium sinks for about one second, then explodes. The explosion is over 50 times the size of the size of the element dropped in the water, and the explosion is enough to break a common Pyrex [[Beaker]], [[Flask]], or [[Test tube|Test Tube]].  You can find a video of the reaction [https://www.youtube.com/watch?v=5Vd5pqjbWJU here.]

 

File:Cesium water.theora.ogv|Addition of a small amount of caesium to cold water is explosive.

 

File:CsCl polyhedra.png|27 small grey spheres in 3 evenly spaced layers of nine. 8 spheres form a regular cube and 8 of those cubes form a larger cube.

 

File:CsX@DWNT.jpg|Monatomic caesium halide wires grown inside double-wall [[carbon nanotube]]s ([[transmission electron microscopy|TEM image]]).

 

File:Cs11O3 cluster.png|{{chem|Cs|11|O|3}} cluster

 

File:Cs-137-decay.svg|Cs-137 decay diagram

 

File:Pollucite-RoyalOntarioMuseum-Jan18-09.jpg|Pollucite, a caesium mineral

==References==

== References ==

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[[Category:Alkali metals]]

[[Category:Alkali metals]]