View source for Caesium

{{Elementbox
|name=caesium
|number=55
|symbol=Cs
|left=[[Xenon|Xe]]
|right=[[Barium|Ba]]
|above=[[Rubidium|Rb]]
|below=[[Francium|Fr]]
|series=[[alkali metal]]s
|series comment=
|group=1
|period=6
|block=s
|series color=#ff6666
|phase color=black
|appearance=silvery gold
|image name=Csmetal.jpg
|image size=
|image name 2=
|image name 2 comment=
|atomic mass=132.9054519
|atomic mass 2=
|atomic mass comment=
|electron configuration=&#91;[[xenon|Xe]]&#93; 6s<sup>1</sup>
|electrons per shell=2, 8, 18, 18, 8, 1
|color=
|phase=solid
|phase comment=
|density gplstp=
|density gpcm3nrt=1.93
|density gpcm3nrt 2=
|density gpcm3mp=1.843
|melting point K=301.59
|melting point C=28.44
|melting point F=83.19
|melting point pressure=
|boiling point K=944
|boiling point C=671
|boiling point F=1240
|boiling point pressure=
|triple point K=
|triple point kPa=
|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
|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=
|magnetic ordering=[[paramagnetic]]<ref name=magnet>[http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elementmagn.pdf Magnetic susceptibility of the elements and inorganic compounds], in Handbook of Chemistry and Physics 81th edition, CRC press. </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.=
|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
|EC number=231-155-4
|isotopes=
{{Elementbox_isotopes_stable | mn=133 | sym=Cs | na=100% | n=78 }}
{{Elementbox_isotopes_decay2 | mn=134 | sym=Cs
 | na=[[synthetic radioisotope|syn]] | hl=65.159 [[megasecond|Ms]]<br />(2.0648 [[years|y]])
 | dm1=[[electron capture|ε]] | de1=1.229 | pn1=134 | ps1=[[xenon|Xe]]
 | dm2=[[beta emission|β<sup>−</sup>]] | de2=2.059 | pn2=134 | ps2=[[barium|Ba]] }}
{{Elementbox_isotopes_decay | mn=135 | sym=Cs
 | na=[[trace radioisotope|trace]] | hl=73 [[terasecond|Ts]]<br />(2.3 [[megayear|My]])
 | dm=[[beta emission|β<sup>−</sup>]] | de=0.269 | pn=135 | ps=[[barium|Ba]] }}
{{Elementbox_isotopes_decay | mn=137 | sym=Cs
 | na=[[synthetic radioisotope|syn]] | hl=948.9 Ms<br />(30.07 y)
 | dm=[[beta emission|β<sup>−</sup>]] | de=1.176 | pn=137 | ps=[[barium|Ba]] }}
|isotopes comment=
}}
'''Caesium''' or '''cesium''' ({{pronEng|ˈsiːziəm}}) is the [[chemical element]] with the symbol '''Cs''' and [[atomic number]] 55. It is a soft, silvery-gold [[alkali metal]] with a melting point of {{nowrap|28 °C}} {{nowrap|(83 °F)}}, which makes it one of only [[liquid metal|five metals]] that are liquid at or near [[room temperature]].<ref>Along with [[rubidium]] ({{nowrap|39 °C}} {{nowrap|[102 °F]}}), [[francium]] ({{nowrap|27 °C}} {{nowrap|[81 °F]}}), [[mercury (element)|mercury]] ({{nowrap|−39 °C}} {{nowrap|[−38 °F]}}), and [[gallium]] ({{nowrap|30 °C}} {{nowrap|[86 °F]}}). <br>Bromine is also liquid at room temperature (-7.2 °C, 19 °F) but it is not a metal, but a [[halogen]].</ref>  Caesium is most notably used in [[atomic clock]]s.

''Caesium'' is the international spelling standardized by the [[IUPAC]], but in the United States it is more commonly spelled as ''cesium''.<ref>IUPAC [http://old.iupac.org/reports/periodic_table/index.html Periodic Table of the Elements]</ref>

==Characteristics==
[[Image:Cesium133Cesium.JPG|thumb|left|200px|High purity caesium metal.]]
The [[emission spectrum]] of caesium has two bright lines in the blue area of the spectrum along with several other lines in the red, yellow, and green areas. This metal is silvery gold in color and is both soft and ductile. Caesium has the lowest [[ionization potential]] of the [[chemical element]]s. Caesium is the least abundant of the five non-radioactive alkali metals. ([[Francium]] is the least common alkali metal but it has no stable isotopes.<ref>{{cite journal
| url=http://chemeducator.org/sbibs/s0010005/spapers/1050387gk.htm
| journal=The Chemical Educator
| volume=10
| issue=5
| month=09/23
| year=2005
| doi=10.1333/s00897050956a
| title=Francium (Atomic Number 87), the Last Discovered Natural Element
| first=Jean-Pierre
| last=Adloff
| coauthors=[[George B. Kauffman]]
| accessdate=2006-05-16}}</ref>).

Caesium, [[gallium]], [[francium]], [[rubidium]], and [[mercury (element)|mercury]] are the only pure metals liquid at or near room temperature. (Some [[NaK|sodium-potassium alloys]] are also liquid at room temperature.) Caesium reacts explosively in cold [[water (molecule)|water]] and also reacts with ice at temperatures above {{nowrap|&minus;116 °C}} {{nowrap|(&minus;177 °F}}, 157&nbsp;K).

[[Caesium hydroxide]] (CsOH) is a very strong [[base (chemistry)|base]] and will rapidly etch the surface of [[glass]]. CsOH is often stated to be the "strongest base", but in fact many compounds such as [[N-Butyllithium|''n''-butyllithium]] and [[sodium amide]] are stronger but are not classic hydroxide bases and are destroyed by water.

==Applications==
Probably the most widespread use of caesium today is in [[caesium formate]]-based [[drilling fluid]]s for the oil industry. The high density of the caesium formate brine (up to 2.3 [[Specific gravity|sg]]), coupled with the relatively benign nature of natural caesium (which has minimal radioactivity because it is almost entirely composed of a [[stable istotope]]), reduces the requirement for toxic high-density suspended solids in the drilling fluid, which is a significant technological, engineering and environmental advantage.<ref> [http://www.spe.org/elibinfo/eLibrary_Papers/spe/2006/06DC/SPE-99068-MS/SPE-99068-MS.htm Drilling and Completing Difficult HP/HT Wells With the Aid of Cesium Formate Brines-A Performance Review]</ref><ref>[http://w1.cabot-corp.com/controller.jsp?N=23+4294966885+1000&entry=product Overview: Cesium Formate Fluids]</ref>
 
Caesium is also used in [[atomic clock]]s, which are accurate to seconds over many thousands of years. Since 1967, the [[SI|International System of Measurements]] has based its unit of [[time]], the [[second]], on the properties of caesium. The [[International System of Units]] (SI) defines the [[second]] as 9,192,631,770 cycles of the [[Radioactive decay|radiation]], which corresponds to the transition between two [[hyperfine structure|hyperfine]] [[energy level]]s of the [[ground state]] of the <sup>133</sup>Cs [[atom]].

*<sup>134</sup>Cs has been used in [[hydrology]] as a measure of caesium output by the [[nuclear power]] industry. This [[isotope]] is used because, while it is less prevalent than either <sup>133</sup>Cs or [[Cs-137|<sup>137</sup>Cs]], <sup>134</sup>Cs can be produced solely by nuclear reactions. <sup>135</sup>Cs has also been used in this function.  
*Like other elements of group 1, caesium has a great affinity for [[oxygen]] and is used as a "[[getter]]" in [[vacuum tube]]s.  
*This metal is also used in [[photoelectric cell]]s due to its ready emission of [[electron]]s.
*Caesium was used as a propellant in early [[ion engines]]. It used a method of ionization to strip the outer electron from the propellant by simple contact with tungsten. Caesium use as a propellant was discontinued when [[Hughes Research Laboratory]] conducted a study finding [[xenon]] gas as a suitable replacement.
*Caesium is used as a [[catalyst]] in the [[hydrogenation]] of certain [[organic compound]]s.  
*[[Radioactive decay|Radioactive]] isotopes of caesium are used in the medical field to treat certain types of [[cancer]].
*[[Caesium fluoride]] is widely used in [[organic chemistry]] as a [[Base (chemistry)|base]] and as a source of [[anhydrous]] [[fluoride]] ion.
*Caesium vapor is used in many common [[magnetometers]].
*Because of their high density, [[caesium chloride]] solutions are commonly used in molecular biology for density gradient ultracentrifugation, primarily for the isolation of viral particles, subcellular organelles and fractions, and nucleic acids from biological samples.
*[[Caesium nitrate]] is used as an [[Oxidizing agent|oxidizer]] and [[pyrotechnic colorant]] to burn [[silicon]] in [[infrared]] [[Flare (pyrotechnic)|flares]]<ref>[http://www.freepatentsonline.com/6230628.html United States Patent 6230628:  Infrared illumination compositions and articles containing the same]</ref> such as the LUU-19 flare,<ref> [http://www.fas.org/man/dod-101/sys/dumb/luu19.htm LUU-19 Flare]</ref> because it emits much of its light in the [[infrared|near infrared]] spectrum.
*[[Caesium-137]] is an extremely common radioisotope used as a [[gamma ray|gamma]]-emitter in industrial applications such as:
**moisture/density gauges
**leveling gauges
**thickness gauges
**[[well logging]] devices which are used to measure the [[electron density]], which is analogous to the bulk density, of the rock formations.
*Caesium is also used as an [[internal standard]] in [[spectrophotometry]].
*Caesium has been used to reduce the [[radar cross section|radar signature]] of [[exhaust gas|exhaust plumes]] in [[military aircraft]].

==History==
Caesium ([[Latin]] ''caesius'' meaning "blueish grey")<ref>Bunsen quotes [[Aulus Gellius]] [[Noctes Atticae]] II, 26 by [[Nigidius Figulus]]: ''Nostris autem veteribus caesia dicts est quae Graecis, ut Nigidus ait, de colore coeli quasi coelia.''</ref><ref>[[Oxford English Dictionary]], 2nd Edition</ref> was [[spectroscopy|spectroscopically]] discovered by [[Robert Bunsen]] and [[Gustav Kirchhoff]] in 1860 in [[mineral water]] from [[Dürkheim]], [[Germany]]. The residues of 44,000 liters of mineral water yielded several grams of caesium salt for further analysis. Its identification was based upon the bright blue lines in its spectrum and it was the first element discovered by [[spectrum analysis]].<ref name=BuKi1861>{{cite journal
 | title = Chemische Analyse durch Spectralbeobachtungen 
 | pages = 337–381
 | author = G. Kirchhoff, R. Bunsen
 | doi = 10.1002/andp.18611890702 
 | journal = [[Annalen der Physik und Chemie]] 
 | volume = 189 
 | issue = 7
 | year = 1861}}</ref> The first caesium metal was produced in 1882 by electrolysis of caesium chloride by Carl Setterberg. Setterberg received his PhD from [[Friedrich August Kekulé von Stradonitz|Kekule]] and Bunsen for this work. Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical applications.

==Occurrence==
[[Image:Pollucite(CesiumMineral)USGOV.jpg|thumb|left|200px|Pollucite, a caesium mineral.]]
An alkali metal, caesium occurs in [[lepidolite]], [[pollucite]] ([[hydrate]]d [[silicate]] of [[aluminium]] and caesium) and within other sources. One of the world's most significant and rich sources of this metal is at [[Bernic Lake]] in [[Manitoba]]. The deposits there are estimated to contain 300,000 [[tonne|metric tons]] of pollucite ore at an average of composition of 20% caesium by weight.  

It can be isolated by [[electrolysis]] of fused caesium [[cyanide]] and in a number of other ways.  
Exceptionally pure and gas-free caesium can be made by the thermal decomposition of caesium [[azide]].  
The primary compounds of caesium are [[caesium chloride]] and its [[nitrate]]. The price of caesium metal in 1997 was about US$30 per gram, but its compounds are much cheaper.
{{seealso|category:Caesium minerals}}

==Isotopes==
{{main|Isotopes of caesium}}

Caesium has at least 39 known isotopes, which is more than any other element except [[francium]]. The [[atomic mass]]es of these isotopes range from 112 to 151. Even though this element has a large number of isotopes, it has only one naturally occurring stable [[isotope]], <sup>133</sup>Cs. Most of the other isotopes have [[half-life|half-lives]] from a few days to fractions of a second. The [[radiogenic]] isotope [[Caesium-137|<sup>137</sup>Cs]] has been used in hydrologic studies, analogous to the use of [[tritium|<sup>3</sup>H]]. <sup>137</sup>Cs is produced from the detonation of [[nuclear weapon]]s and is produced in [[nuclear power plant]]s, and was released to the atmosphere most notably from the [[Chernobyl accident|1986 Chernobyl meltdown]].
This isotope (<sup>137</sup>Cs) is one of the numerous products of fission, directly issued from the fission of uranium.

[[Image:CsCrystals.JPG|thumb|right|280px|High purity caesium-133 (preserved under argon)]]

Beginning in 1945 with the commencement of [[nuclear weapons testing]], <sup>137</sup>Cs was released into the [[Earth's atmosphere|atmosphere]] where it is not absorbed readily into solution and is returned to the surface of the earth as a component of [[radioactive fallout]]. Once <sup>137</sup>Cs enters the ground water, it is deposited on soil surfaces and removed from the landscape primarily by [[particle transport]]. As a result, the input function of these isotopes cannot be estimated as a function of time. Caesium-137 has a half-life of 30.17 years. It decomposes to barium-137m (a short-lived product of decay) then to a form of nonradioactive barium.

==Precautions==
All alkali metals are highly reactive. Caesium, being one of the heavier [[alkali metal]]s, is also one of the most reactive and is highly [[explosive]] when it comes in contact with [[water]]. The hydrogen gas produced by the reaction is heated by the thermal energy released at the same time, causing ignition and a violent explosion (the same as all alkali metals) - but caesium is so reactive that this explosive reaction can even be triggered by cold water or ice.

Caesium is highly pyrophoric and ignites spontaneously in air to form [[caesium hydroxide]] and various oxides.  
Caesium hydroxide is an extremely strong [[Base (chemistry)|base]], and can etch [[glass]].

Caesium compounds are rarely encountered by most persons. All caesium compounds should be regarded as mildly toxic because of its chemical similarity to [[potassium]]. Large amounts cause [[hyperirritability]] and [[spasms]], but such amounts would not ordinarily be encountered in natural sources, so Cs is not a major chemical environmental pollutant. Rats fed caesium in place of potassium in their diet die,{{Fact|date=June 2008}}<!-- Toxicitxy of Caesium 10.1016/0041-008X(75)90216-1}}--> so this element cannot replace potassium in function in rats.

The [[isotope]]s [[Caesium-134|<sup>134</sup>Cs]] and [[Caesium-137|<sup>137</sup>Cs]] (present in the [[biosphere]] in small amounts as a result of radiation leaks) represent a radioactivity burden which varies depending on location. Radiocaesium does not accumulate in the body as effectively as many other fission products (such as radioiodine and radiostrontium), which are actively accumulated by the body; as with other alkali metals, it washes out of the body relatively quickly in the sweat and urine, unlike strontium which accumulates in the bone.{{Fact|date=June 2008}}<!--Fate of caesium in the environment: Distribution between the abiotic and biotic components of aquatic and terrestrial ecosystems 10.1016/0265-931X(96)89276-9 -->

==See also==
*[[Caesium-137]]
*[[Goiânia accident]], a major radioactive contamination incident involving a rod of caesium chloride.
*[[:Category:Caesium compounds|Caesium compounds]]
*[[Dirty bomb]]

==References==
{{Wikisource1911Enc|Caesium}}
{{reflist}}
*[http://periodic.lanl.gov/elements/55.html Los Alamos National Laboratory - Cesium]</div>
*{{cite web| author=Daniel A. Steck| title=Cesium D Line Data | url=http://george.ph.utexas.edu/~dsteck/alkalidata/cesiumnumbers.pdf| publisher=Los Alamos National Laboratory (technical report LA-UR-03-7943)}}

==External links==
{{Commons|Caesium}}
{{wiktionary|caesium}}
*[http://www.webelements.com/webelements/elements/text/Cs/index.html WebElements.com &ndash; Caesium]
*[http://www.cs.rochester.edu/users/faculty/nelson/cesium/cesium_faq.html Humor site dedicated to caesium]
{{clear}}
{{alkalimetals}}
{{Compact periodic table}}

[[Category:Chemical elements|Caesium]]
[[Category:Alkali metals]]
[[Category:Caesium|*]]

{{Imported from Wikipedia|name=Caesium|id=306650536}}