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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.

Einsteinium, Es

einsteinium sample

Atomic number: 99
Atomic mass: [252] (no stable nuclide)
Natural abundance: -
Isotopes: -

History and Production

Named after Albert Einstein (1879-1955). It was discovered by G.R. Choppin, S.G. Thompson, A. Ghiorso and B.G. Harvey in 1952, in the debris of the first large thermonumclear explosion in the Pacific. The isotope produced was 253Es with a half-life of about 20 days. It can also be prepared in nuclear reactors by irridiating 239Pu with neutron over several years. Of nineteen isotopes being found, 254Es has the longest half-life of 276 days.

Physical Data

It is a silvery, highly radioactive metal. It is biologically harmful due to its intense radiological behavior.

Interatomic distance: -
Melting point: 860C
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] 5f11 7s2
Term symbol: 5I15/2
Electron affinity: -   Electronegativity (Pauline): -
Ionization energy (first, second, third): 619.436, -, - kJ/mol

Chemical properties

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