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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.

Lanthanum, La

lanthanum sample

Atomic number: 57
Atomic mass: 138.9055(2)
Natural abundance: 35 ppm
Isotopes:
138La (137.907107) - 0.0902%
139La (138.906348) - 99.9098%

History and Production

From Greek lanthanein, meaning to lie hidden. About 1839, C.G. Mosander extracted lanthanum oxide from impure cerium nitrate. However, relatively pure metal was only obtained in 1923 by electrolysis of fused halides. The main source of the metal can now be obtained from monazite (MPO4) and bastnaesite (MCO3F) where M is the mixture of rare earth metals. The metal compound can be isolated from others by means of selective complexation process and ion-exchange technique. The metal can be isolated by reduction of the fluoride with calcium metal. It is one of the main constituent (25%) of the Misch metal used in making lighter flints. It is also used in carbon lighting by motion picture industry. Its oxide is used in optical glasses to impart sparkle effect and improves resistance to alkali attacks.

Physical Data

It is a rather soft silvery-white metal than can be cut with a knife. It is usually found (35 ppm of earth's crustal rocks) with other rare earth metals in cerite, monazite and bastnaesite.

Interatomic distance: 374.2 pm
Melting point: 918C
Boiling point: 3464C
Thermal conductivity/Wm-1K-1: 13.5 (27C)
Density/kgm-3: 6145 (25C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 431.0 kJ/mol
Gibbs free energy of formation: 393.6 kJ/mol
Entropy: 182.4 J/mol K
Heat capacity: 22.8 J/mol K

Electronic data

Electronic configuration: [Xe] 5d1 6s2
Term symbol: 2D3/2
Electron affinity: 45.3481 kJ/mol   Electronegativity (Pauline): 1.10
Ionization energy (first, second, third): 538.099, 1067.13, 1850.33 kJ/mol

Chemical properties


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