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Element Fact
In 1961, the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis of atomic weight, which has a mass of exactly 12.000 atomic mass unit.

Thorium, Th

thorium sample

Atomic number: 90
Atomic mass: 232.0381(1)
Natural abundance: 8.1 ppm
Isotopes:
229Th (229.031755) - *%
232Th (232.038050) - 100%

History and Production

From the word Thor, Scandinavian god of war. It was discovered by J.J Berzelius from a Norwegian ore known as 'thorite' (ThSiO4) in 1828. It is commercially recovered from monazite sands which contain about 3-9% of the oxide. The metal can be produced by the reduction of its oxide with calcium. Its main use is in gas mantle that improves the low luminosity of the coal-gas flame. It is also used as an alloying agent with magnesium to give high strength and creep resistance. The oxide is used in making high quality lenses with high refractive index and low dispersion. The metal has potential use as a source of nuclear reactor and work has been done in developing thorium cycle convertor-reactor systems.

Physical Data

Pure thorium is a silvery-white metal. It is soft and very ductile. However, its physical properties are greatly influenced by the presence of contaminant. When contaminated with the oxide, the metal slowly tarnishes in air and becoming black. It is quite widely distributed, about 8.1 ppm of the earth's crustal rocks. It is often found in monazite sands, thorite and also in thorianite, a mixture of thorium and uranium oxides.

Interatomic distance: 359.6 pm
Melting point: 1750C
Boiling point: 4788C
Thermal conductivity/Wm-1K-1: 54 (27C)
Density/kgm-3: 11720 (20C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 602 kJ/mol
Gibbs free energy of formation: 560.7 kJ/mol
Entropy: 190.2 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Rn] 6d2 7s2
Term symbol: 3F2
Electron affinity: -   Electronegativity (Pauline): 1.3
Ionization energy (first, second, third): 608.504, 1109.58, 1929.71 kJ/mol

Chemical properties


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