Caesium

55

Cs

132.905451

  • Name: Caesium
  • Symbol: Cs
  • Atomic number: 55
  • Atomic weight: 132.905451
  • CAS Registry ID: 7440-46-2
  • Group name: Alkali metal
  • Period number: 6
  • Block: s-block
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Description

Cesium is an alkali metal that has a bright gold color in its natural solid state. While cesium is considered to be a solid, it has a low melting point and is a liquid near room temperatures. Cesium is the least abundant non-radioactive alkali metal, and is the second most electropositive alkali metal. Cesium has an atomic weight of 132.9054519, a melting point of 83.19 °F, and a boiling point of 1240 °F. Cesium is most commonly used as a drilling fluid for oil.

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Isolation

Cesium is found in nature with other compounds in mineral ore. Multiple isolation procedures are used to extract cesium from its ore.

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Cesium occurs in such minerals as lepidolite and pollucite. Lepidolite is a phyllosilicate mineral that contains cesium in addition to many other minerals, and phyllosilicate is a xeolite mineral. Most of the cesium that is extracted for commercial uses comes from phyllosilicate. Electrolysis of cesium cyanide, and thermal decomposition of its azide form are some of the ways in which cesium can be isolated. The extraction process of cesium includes melting the ore it occurs in and extracting the liquid cesium chloride; electrolysis using cesium as the positive cathode and chlorine as the anode can further isolate the cesium. Cesium can also be extracted from cesium chloride by heating the compound to a molten liquid and adding metallic sodium to the mixture. During this reaction, the cesium becomes highly volatile and pure cesium and sodium chloride are produced. Further distillation processes can remove any contaminants that might be present in small amounts.


General
Name Caesium
Symbol Cs
Number 55
Chemical series alkali metals
Group 1
Period 6
Block s
Appearance silvery gold
Standard atomic weight 132.9054519(2)  g·mol−1
Electron configuration [Xe] 6s1
Electrons per shell 2, 8, 18, 18, 8, 1
Atomic properties
Crystal structure body centered cubic
Oxidation states 1 (strongly basic oxide)
Electronegativity 0.79 (scale Pauling)
Ionization energies 1st: 375.7 kJ/mol
(more) 2nd: 2234.3 kJ/mol
(more) 3rd: 3400 kJ/mol
Atomic radius 260  pm
Atomic radius (calc.) 298 pm
Covalent radius 225 pm
Van der Waals radius
Physical properties
Phase solid
Density (near r.t.) 1.93  g·cm−3
Liquid density at m.p. 1.843  g·cm−3
Melting point 301.59 K (28.44 °C, 83.19 °F)
Boiling point 944 K (671 °C, 1240 °F)
Critical point 1938 K, 9.4 MPa
Heat of fusion 2.09  kJ·mol−1
Heat of vaporization 63.9  kJ·mol−1
Heat capacity (25 °C) 32.210  J·mol−1·K−1
Miscellaneous
Magnetic ordering
Electrical resistivity (20 °C) 205 n Ω·m
Thermal conductivity (300 K) 35.9  W·m−1·K−1
Thermal expansion (25 °C) 97  µm·m−1·K−1
Speed of sound (thin rod)
Young's modulus 1.7  GPa
Shear modulus
Bulk modulus 1.6  GPa
Poisson ratio
Mohs hardness 0.2
Vickers hardness
Brinell hardness 0.14 MPa
CAS registry number 7440-46-2

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