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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.

Francium, Fr

francium sample

Atomic number: 87
Atomic mass: [223] (no stable nuclide)
Natural abundance: 2 x 10-18 ppm.
223Fr (223.019731) - *%

History and Production

The name is derived from the country France. It was identified in 1939 by M. Perey and named in honour of her native country. It can be made by bombarding thorium with protons. It has no commercial use except research interests due to its intense radioactivity and all known isotopes are highly unstable. However, it is thought that the francium atoms could be used to probe interactions between electrons and quarks.

Physical Data

Knowledge of its bulk physical properties are not known. It occurs in nature in traces (2 x 10-18 ppm) as a result of the rare decay of 227Ac in the 235U series. The decay product, 223Fr, has the longest half-life of all of its isotopes is only 22 minutes.

Interatomic distance: -
Melting point: 27C
Boiling point: 675C
Thermal conductivity/Wm-1K-1: 15 (27C)
Density/kgm-3: n/a

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: -
Gibbs free energy of formation: -
Entropy: -
Heat capacity: -

Electronic data

Electronic configuration: [Rn] 7s1
Term symbol: 2S1/2
Electron affinity: 44.3833 kJ/mol   Electronegativity (Pauline): 0.7
Ionization energy (first, second, third): 392.956, -, - kJ/mol

Chemical properties

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