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Element Fact
Americium is one of the few radioactive elements that find its use in homes as a smoke detector.

Actinium, Ac

actinium sample

Atomic number: 89
Atomic mass: [227] (no stable nuclide)
Natural abundance: -
227Ac (227.027747) - *%

History and Production

From Greek aktis, meaning beam or ray. It was discovered by A. Debierne in 1899 and independently by F. Giesel in 1902. It can be produced (in milligram quantity) by the neutron irradiation of 226Ra in a nuclear reactor. Ion-exchange and solvent extraction techniques are used to separate the element. It is used as a source for neutrons.

Physical Data

Actinium glows in the dark due to its intense radioactivity. It is found only in traces in uranium ores as 227Ac, an a and b emitter with a half-life of 21.77 years. One tonne of uranium ore contains only 0.2 mg of actinium.

Interatomic distance: 375.6 pm
Melting point: 1051C
Boiling point: 3200300C
Thermal conductivity/Wm-1K-1: 12 (27C)
Density/kgm-3: 10060 (20C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 406 kJ/mol
Gibbs free energy of formation: 366 kJ/mol
Entropy: 188.1 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Rn] 6d1 7s2
Term symbol: 2D3/2
Electron affinity: 33.7699 kJ/mol   Electronegativity (Pauline): 1.1
Ionization energy (first, second, third): 498.830, 1167.47, - kJ/mol

Chemical properties

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