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'''Caesium''' (or '''cesium''') is the [[chemical element]] with the [[atomic number]] 55 on the [[periodic table]]. Its symbol is '''Cs'''.
{{Elementbox
|number=55
|symbol=Cs
|name=caesium
|pronounce={{IPAc-en|ˈ|s|iː|z|i|ə|m}} {{respell|SEE|zee-əm}}
|left=[[xenon]]
|right=[[barium]]
|above=[[rubidium|Rb]]
|below=[[francium|Fr]]
|series=alkali metal
|series comment=
|group=1
|period=6
|block=s
|appearance=silvery gold
|image name=Cesium.jpg
|image size=
|image alt=Some silvery-gold metal, with a liquid-like texture and lustre, sealed in a glass ampoule
|atomic mass= 132.90545196
|atomic mass 2=6
|electron configuration=[[[xenon|Xe]]] 6s<sup>1</sup>
|electrons per shell= 2, 8, 18, 18, 8, 1
|density gpcm3nrt=1.93
|density gpcm3mp=1.843
|melting point K=301.7
|melting point C=28.5
|melting point F=83.3
|melting point pressure=
|boiling point K=944
|boiling point C=671
|boiling point F=1240
|boiling point pressure=
|triple point K=
|triple point kPa=
|triple point K 2=
|triple point kPa 2=
|critical point K=1938
|critical point MPa=9.4
|heat fusion=2.09
|heat fusion 2=
|heat fusion pressure=
|heat vaporization=63.9
|heat vaporization pressure=
|heat capacity=32.210
|heat capacity pressure=
|vapor pressure 1=418
|vapor pressure 10=469
|vapor pressure 100=534
|vapor pressure 1 k=623
|vapor pressure 10 k=750
|vapor pressure 100 k=940
|vapor pressure comment=
|crystal structure=body-centered cubic
|oxidation states='''1''', −1<br />(strongly [[base (chemistry)|basic]] oxide)
|oxidation states comment=
|electronegativity=0.79
|number of ionization energies=3
|1st ionization energy=375.7
|2nd ionization energy=2234.3
|3rd ionization energy=3400
|atomic radius=265
|atomic radius calculated=
|covalent radius=244±11
|Van der Waals radius=[[1 E-10 m|343]]
|magnetic ordering= [[paramagnetic]]<ref name=magnet>{{cite book|url=http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elementmagn.pdf|format=PDF|chapter=Magnetic susceptibility of the elements and inorganic compounds|title=Handbook of chemistry and physics|edition=87th|publisher=CRC press|accessdate=2010-09-26|isbn=0-8493-0487-3}}</ref>
|electrical resistivity=
|electrical resistivity at 0=
|electrical resistivity at 20=205 n
|thermal conductivity=35.9
|thermal conductivity 2=
|thermal diffusivity=
|thermal expansion=
|thermal expansion at 25=97
|speed of sound=
|speed of sound rod at 20=
|speed of sound rod at r.t.=
|Tensile strength=
|Young's modulus=1.7
|Shear modulus=
|Bulk modulus=1.6
|Poisson ratio=
|Mohs hardness=0.2
|Vickers hardness=
|Brinell hardness=0.14
|CAS number=7440-46-2
}}<noinclude>
Caesium is an [[alkali]] [[metal]]. Its [[melt]]ing point is low (28 °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 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, it is mildly poisonous because it is close to [[potassium]], which the body does need.
== 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. 337–381 ({{DOI|10.1002/andp.18611890702}}).</ref>
== 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 forms [[Chemical compound|compounds]] with many other [[chemical element]]s. Caesium formate is used in oil drilling because of its high [[density]].
==References==
{{reflist}}
{{Periodic Table}}
[[Category:Alkali metals]]
[[Category:Chemical elements]]
{{Link FA|de}}
{{Link FA|en}}
{{Link GA|ja}}
{{Elementbox
|number=55
|symbol=Cs
|name=caesium
|pronounce={{IPAc-en|ˈ|s|iː|z|i|ə|m}} {{respell|SEE|zee-əm}}
|left=[[xenon]]
|right=[[barium]]
|above=[[rubidium|Rb]]
|below=[[francium|Fr]]
|series=alkali metal
|series comment=
|group=1
|period=6
|block=s
|appearance=silvery gold
|image name=Cesium.jpg
|image size=
|image alt=Some silvery-gold metal, with a liquid-like texture and lustre, sealed in a glass ampoule
|atomic mass= 132.90545196
|atomic mass 2=6
|electron configuration=[[[xenon|Xe]]] 6s<sup>1</sup>
|electrons per shell= 2, 8, 18, 18, 8, 1
|density gpcm3nrt=1.93
|density gpcm3mp=1.843
|melting point K=301.7
|melting point C=28.5
|melting point F=83.3
|melting point pressure=
|boiling point K=944
|boiling point C=671
|boiling point F=1240
|boiling point pressure=
|triple point K=
|triple point kPa=
|triple point K 2=
|triple point kPa 2=
|critical point K=1938
|critical point MPa=9.4
|heat fusion=2.09
|heat fusion 2=
|heat fusion pressure=
|heat vaporization=63.9
|heat vaporization pressure=
|heat capacity=32.210
|heat capacity pressure=
|vapor pressure 1=418
|vapor pressure 10=469
|vapor pressure 100=534
|vapor pressure 1 k=623
|vapor pressure 10 k=750
|vapor pressure 100 k=940
|vapor pressure comment=
|crystal structure=body-centered cubic
|oxidation states='''1''', −1<br />(strongly [[base (chemistry)|basic]] oxide)
|oxidation states comment=
|electronegativity=0.79
|number of ionization energies=3
|1st ionization energy=375.7
|2nd ionization energy=2234.3
|3rd ionization energy=3400
|atomic radius=265
|atomic radius calculated=
|covalent radius=244±11
|Van der Waals radius=[[1 E-10 m|343]]
|magnetic ordering= [[paramagnetic]]<ref name=magnet>{{cite book|url=http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elementmagn.pdf|format=PDF|chapter=Magnetic susceptibility of the elements and inorganic compounds|title=Handbook of chemistry and physics|edition=87th|publisher=CRC press|accessdate=2010-09-26|isbn=0-8493-0487-3}}</ref>
|electrical resistivity=
|electrical resistivity at 0=
|electrical resistivity at 20=205 n
|thermal conductivity=35.9
|thermal conductivity 2=
|thermal diffusivity=
|thermal expansion=
|thermal expansion at 25=97
|speed of sound=
|speed of sound rod at 20=
|speed of sound rod at r.t.=
|Tensile strength=
|Young's modulus=1.7
|Shear modulus=
|Bulk modulus=1.6
|Poisson ratio=
|Mohs hardness=0.2
|Vickers hardness=
|Brinell hardness=0.14
|CAS number=7440-46-2
}}<noinclude>
Caesium is an [[alkali]] [[metal]]. Its [[melt]]ing point is low (28 °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 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, it is mildly poisonous because it is close to [[potassium]], which the body does need.
== 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. 337–381 ({{DOI|10.1002/andp.18611890702}}).</ref>
== 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 forms [[Chemical compound|compounds]] with many other [[chemical element]]s. Caesium formate is used in oil drilling because of its high [[density]].
==References==
{{reflist}}
{{Periodic Table}}
[[Category:Alkali metals]]
[[Category:Chemical elements]]
{{Link FA|de}}
{{Link FA|en}}
{{Link GA|ja}}