Eu Gd Tb Am Cm Bk -- -- -- 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.

Curium, Cm Atomic number: 96 Atomic mass: [247] (no stable nuclide) Natural abundance: - Isotopes: - History and Production The name is derived in honor of Pierre and Marie Curie. It was the third transuranium element to be discovered, after neptunium and plutonium. It was produced in 1944 by G.T. Seaborg, R.A. James and A. Ghiorso by bombardment of 239Pu with helium ion. There is no use for the element apart for research purposes. However, 242Cm has been suggested to be used as a power source. Physical Data It is a silvery radioactive metal. It is more electropositive than aluminium. The most stable isotope, 247Cm has a half-life of about 16 million years. It is thought that natural curium many exist in traces in uranium ores. It is radiologically highly toxic which readily accumulated in the bone. Interatomic distance: - Melting point: 1345°C Boiling point: n/a Thermal conductivity/Wm-1K-1: 10 est. (27°C) Density/kgm-3: 13510 est. Standard Thermodynamic Data (atomic gas) Enthalpy of formation: - Gibbs free energy of formation: - Entropy: - Heat capacity: - Electronic data Electronic configuration: [Rn] 5f7 6d1 7s2 Term symbol: 8S7/2 Electron affinity: -   Electronegativity (Pauline): - Ionization energy (first, second, third): 578.092, -, - kJ/mol Chemical properties

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