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Caesium

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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Caesium

Description

Isolation

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