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Element Fact
Rhenium was the last naturally occurring element to be identified, in 1925. It was so rare that only 1 g of the metal was extracted out of 660 kg of molybdenite ore.

Cerium, Ce

cerium sample

Atomic number: 58
Atomic mass: 140.116(1)
Natural abundance: 66 ppm
136Ce (135.90714) - 0.19%
137Ce (136.90778) - -%
138Ce (137.90599) - 0.25%
139Ce (138.906647) - -%
140Ce (139.905434) - 88.48%
141Ce (140.908271) - -%
142Ce (141.909240) - 11.08%

History and Production

Named after the asteroid Ceres, the Roman goddess of agriculture, discovered in 1801. Cerium was discovered in 1803 by J.J. Berzelius, W. Hisinger and independently, by M. Klaproth. It is commercially extracted from monazite (MPO4, M = Ce, Th, La etc.) and bastnaesite (MCO3F, M = La, Ce etc.) The metal is obtained by reducing its fluoride with calcium metal. It can also be obtained by electrolysis of fused chloride. It is one of the constituent in misch metal for making lighter flints. Cerium is also used as a getter of noble gas in vacuum apparatus. With other rare earths it is used as carbon-arc lighting and as catalysts in petroleum refining. The isotope 144Ce is also used as a source for electron emitter.

Physical Data

It has steel-grey in appearance, rather soft and ductile. It tarnishes in air and readily burn to give the oxide (CeO2). It has about 66 ppm in natural abundance, usually associates with other rare earth metals in monazite sand, bastnaesite, samarskite, cerite etc.

Interatomic distance: 365 pm
Melting point: 798C
Boiling point: 3424C
Thermal conductivity/Wm-1K-1: 11.4 (27C)
Density/kgm-3: 8240 (a), 6749 (b), 6773 (g), 6700 (d) all at 25C

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 423.0 kJ/mol
Gibbs free energy of formation: 385.0 kJ/mol
Entropy: 191.8 J/mol K
Heat capacity: 23.1 J/mol K

Electronic data

Electronic configuration: [Xe] 4f1 5d1 6s2
Term symbol: 3H4
Electron affinity: -   Electronegativity (Pauline): 1.12
Ionization energy (first, second, third): 534.404, 1046.87, 1948.81 kJ/mol

Chemical properties

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