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Actinium (Ac)

From Wikipedia, the free encyclopediaActinium is a radioactive chemical element with symbol Ac (not to be confused with the abbreviation for an acetyl group) and atomic number 89, which was discovered in 1899. It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902.

Actinium in the periodic table

Atomic number89
Element categoryActinide

Physical properties

Phase at STPSolid
Density10 g/cm3
Atomic weight227 u
Melting point1500 K
1226.85 °C
2240.33 °F
Boiling point3500 K
3226.85 °C
5840.33 °F

Atomic properties

Electronegativity (Pauling Scale)1.1
Electron affinity33.77 kJ/mol
Oxidation states+3
(a strongly basic oxide)
Ionization energies
1499 kJ/mol
21170 kJ/mol
31900 kJ/mol
44700 kJ/mol

Electron configuration

Elektronkonfiguration (shorthand)[Rn] 6d1 7s2
Electron configuration1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 6d1 7s2
Electrons per shell2, 8, 18, 32, 18, 9, 2


Discovered byFriedrich Oskar Giesel
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