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'''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''' 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 and in several other ountries it is spelled as ''cesium'' because the "ae" combination is practically obsolete now.<ref>IUPAC [http://old.iupac.org/reports/periodic_table/index.html Periodic Table of the Elements]</ref>
''Caesium'' is the international spelling standardized by the [[IUPAC]], but in the United States it is spelled as ''cesium''.<ref>IUPAC [http://old.iupac.org/reports/periodic_table/index.html Periodic Table of the Elements]</ref>


==Characteristics==
==Characteristics==

Revision as of 18:01, 24 June 2009

Caesium, 55Cs
Some pale gold metal, with a liquid-like texture and lustre, sealed in a glass ampoule
Caesium
Pronunciation/ˈsziəm/ (SEE-zee-əm)
Alternative namecesium (US)
Appearancepale gold
Standard atomic weight Ar°(Cs)
Caesium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Rb

Cs

Fr
xenoncaesiumbarium
Atomic number (Z)55
Groupgroup 1: hydrogen and alkali metals
Periodperiod 6
Block  s-block
Electron configuration[Xe] 6s1
Electrons per shell2, 8, 18, 18, 8, 1
Physical properties
Phase at STPsolid
Melting point301.7 K ​(28.5 °C, ​83.3 °F)
Boiling point944 K ​(671 °C, ​1240 °F)
Density (at 20° C)1.886 g/cm3[3]
when liquid (at m.p.)1.843 g/cm3
Critical point1938 K, 9.4 MPa[4]
Heat of fusion2.09 kJ/mol
Heat of vaporization63.9 kJ/mol
Molar heat capacity32.210 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 418 469 534 623 750 940
Atomic properties
Oxidation states−1, +1[5] (a strongly basic oxide)
ElectronegativityPauling scale: 0.79
Ionization energies
  • 1st: 375.7 kJ/mol
  • 2nd: 2234.3 kJ/mol
  • 3rd: 3400 kJ/mol
Atomic radiusempirical: 265 pm
Covalent radius244±11 pm
Van der Waals radius343 pm
Color lines in a spectral range
Spectral lines of caesium
Other properties
Natural occurrenceprimordial
Crystal structurebody-centered cubic (bcc) (cI2)
Lattice constant
Bodycentredcubic crystal structure for caesium
a = 616.2 pm (at 20 °C)[3]
Thermal expansion92.6×10−6/K (at 20 °C)[3]
Thermal conductivity35.9 W/(m⋅K)
Electrical resistivity205 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[6]
Young's modulus1.7 GPa
Bulk modulus1.6 GPa
Mohs hardness0.2
Brinell hardness0.14 MPa
CAS Number7440-46-2
History
Namingfrom Latin caesius 'bluish grey', for its spectral colours
DiscoveryRobert Bunsen and Gustav Kirchhoff (1860)
First isolationCarl Setterberg (1882)
Isotopes of caesium
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
| references

Caesium or cesium (Template:PronEng) 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 28 °C (83 °F), which makes it one of only five metals that are liquid at or near room temperature.[9] Caesium is most notably used in atomic clocks.

Caesium is the international spelling standardized by the IUPAC, but in the United States it is spelled as cesium.[10]

Characteristics

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 elements. 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.[11]).

Caesium, gallium, francium, rubidium, and mercury are the only pure metals liquid at or near room temperature. (Some sodium-potassium alloys are also liquid at room temperature.) Caesium reacts explosively in cold water and also reacts with ice at temperatures above −116 °C (−177 °F, 157 K).

Caesium hydroxide (CsOH) is a very strong 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 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 fluids for the oil industry. The high density of the caesium formate brine (up to 2.3 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.[12][13]

Caesium is also used in atomic clocks, which are accurate to seconds over many thousands of years. Since 1967, the 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 radiation, which corresponds to the transition between two hyperfine energy levels of the ground state of the 133Cs atom.

History

Caesium (Latin caesius meaning "blueish grey")[16][17] was 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.[18] The first caesium metal was produced in 1882 by electrolysis of caesium chloride by Carl Setterberg. Setterberg received his PhD from 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

Pollucite, a caesium mineral.

An alkali metal, caesium occurs in lepidolite, pollucite (hydrated 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 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.

Isotopes

Caesium has at least 39 known isotopes, which is more than any other element except francium. The atomic masses 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, 133Cs. Most of the other isotopes have half-lives from a few days to fractions of a second. The radiogenic isotope 137Cs has been used in hydrologic studies, analogous to the use of 3H. 137Cs is produced from the detonation of nuclear weapons and is produced in nuclear power plants, and was released to the atmosphere most notably from the 1986 Chernobyl meltdown. This isotope (137Cs) is one of the numerous products of fission, directly issued from the fission of uranium.

High purity caesium-133 (preserved under argon)

Beginning in 1945 with the commencement of nuclear weapons testing, 137Cs was released into the 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 137Cs 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 metals, 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, 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,[citation needed] so this element cannot replace potassium in function in rats.

The isotopes 134Cs and 137Cs (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.[citation needed]

See also

References

  1. ^ "Standard Atomic Weights: Caesium". CIAAW. 2013.
  2. ^ 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. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  3. ^ a b c Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
  4. ^ 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.
  5. ^ Dye, J. L. (1979). "Compounds of Alkali Metal Anions". Angewandte Chemie International Edition. 18 (8): 587–598. doi:10.1002/anie.197905871.
  6. ^ "Magnetic susceptibility of the elements and inorganic compounds". Handbook of Chemistry and Physics (PDF) (87th ed.). CRC press. ISBN 0-8493-0487-3. Retrieved 2010-09-26.
  7. ^ 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.
  8. ^ "NIST Radionuclide Half-Life Measurements". NIST. Retrieved 2011-03-13.
  9. ^ Along with rubidium (39 °C [102 °F]), francium (27 °C [81 °F]), mercury (−39 °C [−38 °F]), and gallium (30 °C [86 °F]).
    Bromine is also liquid at room temperature (-7.2 °C, 19 °F) but it is not a metal, but a halogen.
  10. ^ IUPAC Periodic Table of the Elements
  11. ^ Adloff, Jean-Pierre (2005). "Francium (Atomic Number 87), the Last Discovered Natural Element". The Chemical Educator. 10 (5). doi:10.1333/s00897050956a. Retrieved 2006-05-16. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  12. ^ Drilling and Completing Difficult HP/HT Wells With the Aid of Cesium Formate Brines-A Performance Review
  13. ^ Overview: Cesium Formate Fluids
  14. ^ United States Patent 6230628: Infrared illumination compositions and articles containing the same
  15. ^ LUU-19 Flare
  16. ^ 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.
  17. ^ Oxford English Dictionary, 2nd Edition
  18. ^ G. Kirchhoff, R. Bunsen (1861). "Chemische Analyse durch Spectralbeobachtungen". Annalen der Physik und Chemie. 189 (7): 337–381. doi:10.1002/andp.18611890702.

External links