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Ho

Er

Tm

Es

Fm

Md

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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.

Fermium, Fm

fermium sample

Atomic number: 100
Atomic mass: [257] (no stable nuclide)
Natural abundance: -
Isotopes: -

History and Production

Named after Enrico Fermi (1901-1954), the atomic physicist. It was identified by A. Ghiorso, G.R. Choppin and co-workers in 1952 from a thermonuclear explosion test in the Pacific. The isotope produced was the 255Fm with a half-life of about 20 hours. However, the discovery was not immediately made known. In early 1954, 250Fm, with a half-life of 30 minutes, was produced by bombardment of 238U with oxygen ions from the Nobel Institute of Physics in Stockholm. Intense neutron irriadiation on plutonium produces other heavier isotopes of fermium. Among twenty isotopes and isomers being discovered, 257Fm is found to have longest half-life of about 100 days.

Physical Data

Its physical data is not known as weighable quantity has not been produced. It is probably silvery white in appearance.

Interatomic distance: -
Melting point: 1527C (est.)
Boiling point: n/a
Thermal conductivity/Wm-1K-1: 10 est. (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: Electronic configuration: [Rn] 5f12 7s2
Term symbol: 3H6
Electron affinity: -   Electronegativity (Pauline): -
Ionization energy (first, second, third): 627.155, -, - kJ/mol

Chemical properties


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