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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.

Gadolinium, Gd

gadolinium sample

Atomic number: 64
Atomic mass: 157.25(3)
Natural abundance: 6.1 ppm
Isotopes:
152Gd (151.919788) - 0.20%
154Gd (153.920862) - 2.18%
155Gd (154.922619) - 14.80%
156Gd (155.922120) - 20.47%
157Gd (156.923957) - 15.65%
158Gd (157.924101) - 24.84%
160Gd (159.927051) - 21.86%

History and Production

Derived from gadolinite, a mineral named after Gadolin, a Finnish chemist. The metal oxide was first discovered by J.C.G. de Marignac and the element was isolated by P.-. Lecoq de Boisbaudran in 1886. The main commercial sources are now obtained from monazite and bastnaesite, which contain a mixture of other rare earth metals. Gadolinium salts can be separated using solvent extraction and ion-exchange techniques. The metal can then be obtained by the reduction of its fluoride with calcium metal. It is used as an alloying agent (~1%) increase the workability and resistance of chromium and iron to high temperatures and oxidation. Gadolinium compounds are used in making phosphors for color television tubes.

Physical Data

It is silvery-white and quite ductile. It tarnishes in moist air to give a loosely adhereing oxide film. The metal exists in two allotropic forms. The a form is hexagonal close-packed while the b form, exists above 1235C, has a body-centered cubic structure. Gadolinium has the highest absorption cross section for thermal neutrons of any element. The natural abundance is about 6.1 ppm of the earth's crust and is usually associated with other rare earth metals.

Interatomic distance: 357.4 pm
Melting point: 1313C
Boiling point: 3273C
Thermal conductivity/Wm-1K-1: 10.6 (27C)
Density/kgm-3: 7900 (25C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 397.5 kJ/mol
Gibbs free energy of formation: 359.8 kJ/mol
Entropy: 194.3 J/mol K
Heat capacity: 27.5 J/mol K

Electronic data

Electronic configuration: [Xe] 4f7 5d1 6s2
Term symbol: 9D2
Electron affinity: -   Electronegativity (Pauline): 1.20
Ionization energy (first, second, third): 593.395, 1166.508, 1990.49 kJ/mol

Chemical properties


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