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Caesium,  55Cs
Some sillery-gowd metal, wi a liquid-like textur an lustre, sealed in a glass ampoule
General properties
Name, seembol caesium, Cs
Appearance sillery gowd
Pronunciation /ˈsziəm/ SEE-zee-əm
Caesium in the periodic cairt
Hydrogen (diatomic nonmetal)
Helium (noble gas)
Lithium (alkali metal)
Beryllium (alkaline yird metal)
Boron (metalloid)
Carbon (polyatomic nonmetal)
Nitrogen (diatomic nonmetal)
Oxygen (diatomic nonmetal)
Fluorine (diatomic nonmetal)
Neon (noble gas)
Sodium (alkali metal)
Magnesium (alkaline yird metal)
Aluminium (post-transeetion metal)
Silicon (metalloid)
Phosphorus (polyatomic nonmetal)
Sulfur (polyatomic nonmetal)
Chlorine (diatomic nonmetal)
Argon (noble gas)
Potassium (alkali metal)
Calcium (alkaline yird metal)
Scandium (transeetion metal)
Titanium (transeetion metal)
Vanadium (transeetion metal)
Chromium (transeetion metal)
Manganese (transeetion metal)
Iron (transeetion metal)
Cobalt (transeetion metal)
Nickel (transeetion metal)
Copper (transeetion metal)
Zinc (transeetion metal)
Gallium (post-transeetion metal)
Germanium (metalloid)
Arsenic (metalloid)
Selenium (polyatomic nonmetal)
Bromine (diatomic nonmetal)
Krypton (noble gas)
Rubidium (alkali metal)
Strontium (alkaline yird metal)
Yttrium (transeetion metal)
Zirconium (transeetion metal)
Niobium (transeetion metal)
Molybdenum (transeetion metal)
Technetium (transeetion metal)
Ruthenium (transeetion metal)
Rhodium (transeetion metal)
Palladium (transeetion metal)
Siller (transeetion metal)
Cadmium (transeetion metal)
Indium (post-transeetion metal)
Tin (post-transeetion metal)
Antimony (metalloid)
Tellurium (metalloid)
Iodine (diatomic nonmetal)
Xenon (noble gas)
Caesium (alkali metal)
Barium (alkaline yird metal)
Lanthanum (lanthanide)
Cerium (lanthanide)
Praseodymium (lanthanide)
Neodymium (lanthanide)
Promethium (lanthanide)
Samarium (lanthanide)
Europium (lanthanide)
Gadolinium (lanthanide)
Terbium (lanthanide)
Dysprosium (lanthanide)
Holmium (lanthanide)
Erbium (lanthanide)
Thulium (lanthanide)
Ytterbium (lanthanide)
Lutetium (lanthanide)
Hafnium (transeetion metal)
Tantalum (transeetion metal)
Tungsten (transeetion metal)
Rhenium (transeetion metal)
Osmium (transeetion metal)
Iridium (transeetion metal)
Platinum (transeetion metal)
Gold (transeetion metal)
Mercur (transeetion metal)
Thallium (post-transeetion metal)
Lead (post-transeetion metal)
Bismuth (post-transeetion metal)
Polonium (post-transeetion metal)
Astatine (metalloid)
Radon (noble gas)
Francium (alkali metal)
Radium (alkaline yird metal)
Actinium (actinide)
Thorium (actinide)
Protactinium (actinide)
Uranium (actinide)
Neptunium (actinide)
Plutonium (actinide)
Americium (actinide)
Curium (actinide)
Berkelium (actinide)
Californium (actinide)
Einsteinium (actinide)
Fermium (actinide)
Mendelevium (actinide)
Nobelium (actinide)
Lawrencium (actinide)
Rutherfordium (transeetion metal)
Dubnium (transeetion metal)
Seaborgium (transeetion metal)
Bohrium (transeetion metal)
Hassium (transeetion metal)
Meitnerium (unkent chemical properties)
Darmstadtium (unkent chemical properties)
Roentgenium (unkent chemical properties)
Copernicium (transeetion metal)
Ununtrium (unkent chemical properties)
Flerovium (post-transeetion metal)
Ununpentium (unkent chemical properties)
Livermorium (unkent chemical properties)
Ununseptium (unkent chemical properties)
Ununoctium (unkent chemical properties)


Atomic nummer (Z) 55
Group, block group 1 (alkali metals), s-block
Period period 6
Element category   alkali metal
Staundart atomic wicht (±) (Ar) 132.9054519(2)
Electron configuration [Xe] 6s1
per shell
2, 8, 18, 18, 8, 1
Pheesical properties
Phase solid
Meltin pynt 301.59 K ​(28.44 °C, ​83.19 °F)
Bylin pynt 944 K ​(671 °C, ​1240 °F)
Density near r.t. 1.93 g/cm3
when liquid, at m.p. 1.843 g/cm3
Creetical pynt 1938 K, 9.4 MPa
Heat of fusion 2.09 kJ/mol
Heat o 63.9 kJ/mol
Molar heat capacity 32.210 J/(mol·K)
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
(strangly basic oxide)
Electronegativity Pauling scale: 0.79
Atomic radius empirical: 265 pm
Covalent radius 244±11 pm
Van der Waals radius 343 pm
Crystal structur body-centered cubic (bcc)
Body-centered cubic crystal structur for caesium
Thermal expansion 97 µm/(m·K) (at 25 °C)
Thermal conductivity 35.9 W/(m·K)
Electrical resistivity 205 n Ω·m (at 20 °C)
Magnetic orderin paramagnetic[1]
Young's modulus 1.7 GPa
Bulk modulus 1.6 GPa
Mohs haurdness 0.2
Brinell haurdness 0.14 MPa
CAS Nummer 7440-46-2
Discovery Robert Bunsen an Gustav Kirchhoff (1860)
First isolation Carl Setterberg (1882)
Maist stable isotopes o caesium
iso NA hauf-life DM DE (MeV) DP
133Cs 100% 133Cs is stable wi 78 neutrons
134Cs syn 2.0648 y ε 1.229 134Xe
β 2.059 134Ba
135Cs trace 2.3×106 y β 0.269 135Ba
137Cs trace 30.17 y[2] β 1.174 137Ba
· references

Caesium or cesium[note 1] is a chemical element wi seembol Cs an atomic nummer 55. It is a saft, sillery-gowd alkali metal wi a meltin pynt o 28 °C (82 °F), which maks it ane o anly five elemental metals that are liquid at or near ruim temperatur.[note 2] Caesium is an alkali metal an haes pheesical an chemical properties seemilar tae those o rubidium an potassium. The metal is extremely reactive an pyrophoric, reactin wi watter even at −116 °C (−177 °F). It is the least electronegative element havin a stable isotope, caesium-133. Caesium is mined maistly frae pollucite, while the radioisotopes, especially caesium-137, a fission product, are extractit frae waste produced bi nuclear reactors.

Twa German chemists, Robert Bunsen an Gustav Kirchhoff, discovered caesium in 1860 bi the newly developed method o flame spectroscopy. The first smaa-scale applications for caesium wur as a "getter" in vacuum tubes an in photoelectric cells. In 1967, a specific frequency frae the emission spectrum o caesium-133 wis chosen tae be uised in the definition o the seicont bi the Internaitional Seestem o Units. Syne then, caesium haes been widely uised in atomic clocks.

Syne the 1990s, the lairgest application o the element haes been as caesium formate for drilling fluids. It haes a range o applications in the production o electricity, in electronics, an in chemistry. The radioactive isotope caesium-137 haes a hauf-life o aboot 30 years an is uised in medical applications, industrial gauges, an hydrology. Altho the element is anly mildly toxic, it is a hazardous material as a metal an its radioisotopes present a heich heal risk if released intae the environment.

Notes[eedit | eedit soorce]

  1. Caesium is the spellin recommendit bi the Internaitional Union o Pure an Applee'd Chemistry (IUPAC).[3] The American Chemical Society (ACS) haes uised the spellin cesium syne 1921,[4][5] follaein Webster's New International Dictionary. The element wis named efter the Latin word cæsius, meanin "bluish gray".[6] Hence, an alternative orthography is cæsium. Mair spellin explanation at ae/oe vs e.
  2. Alang wi rubidium (39 °C [102 °F]), francium (estimatit at 27 °C [81 °F]), mercur (−39 °C [−38 °F]), an gallium (30 °C [86 °F]); bromine is an aa liquid at ruim temperatur (meltin at −7.2 °C, 19 °F) but it is a halogen, nae a metal.

References[eedit | eedit soorce]

  1. "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. 
  2. "NIST Radionuclide Half-Life Measurements". NIST. Retrieved 2011-03-13. 
  3. Internaitional Union o Pure an Applee'd Chemistry (2005). Nomenclature o Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSCIUPAC. ISBN 0-85404-438-8. pp. 248–49. Electronic version..
  4. 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 0-8412-3999-1. 
  5. 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. 
  6. OED entry for "caesium". Second edition, 1989; online version June 2012; accessed 07 September 2012. Earlier version first published in New English Dictionary, 1888.

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