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Element Fact
Iridium is the most corrosion-resistant metal known. Together with platinum, it is used to make the international prototype of the kilogram, which is the standard definition for the unit of mass.

Thulium, Tm

thulium sample

Atomic number: 69
Atomic mass: 168.93421(2)
Natural abundance: 0.5 ppm
169Tm (168.93421) - 100%

History and Production

Named after Thule, the ancient name for Scandinavia. Discovered in 1879 by P.T. Cleve. It is obtained commercially from monazite, a mixture of rare earth phosphates containing about 0.007% of thullium. Ion-exchange and solvent extraction techniques are used to isolate the salts while the metal is obtained by reduction of the oxide with lanthanum metal. The metal can also be recovered from flue dusts emitted during sulfide roasting for sulfuric acid production, and from the smelting of zinc and lead ores. At present time, there is only very few commercial use of the element. It has a potential use in making ceramic magnetic materials in microwave equipment.

Physical Data

It is silver-gray in color, malleable and ductile. It is soft enough to cut by a knife. It is the least abundant element among the lanthanides, about 0.5 ppm of the earth crust and often associate with other rare earth elements.

Interatomic distance: 344.8 pm
Melting point: 1545C
Boiling point: 1950C
Thermal conductivity/Wm-1K-1: 16.8 (27C)
Density/kgm-3: 9321 (25C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 232.2 kJ/mol
Gibbs free energy of formation: 197.5 kJ/mol
Entropy: 190.1 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Xe] 4f13 6s2
Term symbol: 2F7/2
Electron affinity: -   Electronegativity (Pauline): 1.25
Ionization energy (first, second, third): 596.696, 1162.65, 2284.77 kJ/mol

Chemical properties

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