Actinium is a chemical element with the symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name emanium; the element got its name by being wrongly identified with a substance André-Louis Debierne found in 1899 and called actinium. Actinium gave the name to the actinide series, a set of 15 elements between actinium and lawrencium in the periodic table. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated.

A soft, silvery-white radioactive metal, actinium reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that prevents further oxidation. As with most lanthanides and many actinides, actinium assumes oxidation state +3 in nearly all its chemical compounds. Actinium is found only in traces in uranium and thorium ores as the isotope 227Ac, which decays with a half-life of 21. 772 years, predominantly emitting beta and sometimes alpha particles, and 228Ac, which is beta active with a half-life of 6. 15 hours. One tonne of natural uranium in ore contains about 0. 2 milligrams of actinium-227, and one tonne of thorium contains about 5 nanograms of actinium-228. The close similarity of physical and chemical properties of actinium and lanthanum makes separation of actinium from the ore impractical. Instead, the element is prepared, in milligram amounts, by the neutron irradiation of 226Ra in a nuclear reactor. Owing to its scarcity, high price and radioactivity, actinium has no significant industrial use. Its current applications include a neutron source and an agent for radiation therapy.

© Wikipedia | CC-by-SA-3.0 | Read more …

Atomic properties

Atomic mass(227.027 u)

Atomic radii

Covalent radius215 pm

Atomic shell

Electron configurationRn 6d1 7s2
Ionization energy(1st) 5.380226 eV
(2nd) 11.75 eV
(3rd) 17.431 eV
(4th) 44.8 eV
(5th) 55 eV
Shell model

Physical properties

Density10.07 g·cm−3
Molar volume2.255·10-5 m3·mol−1


Melting point1,500 K
Boiling point3,500 ±300 K
Liquid range2,000 K


Melting enthalpy14 kJ·mol-1
Enthalpy of vaporization400 kJ·mol-1
Binding energy406 kJ·mol-1

Heat and conductivity

Thermal conductivity12 W·m-1·K-1



Chemical properties

Basicitymoderately basic
Oxidation state3
Standard potential-2.13 V (Ac3+ + 3e- → Ac)


Pauling scale1.1
Allred-Rochow scale1
Nagle scale1.03

Other properties

Natural occurrenceDecay product
Crystal structureFace-centered cubic
Goldschmidt Classificationsynthetic
Superconductorwithout transition tempperature
Radioactivitysignificantly radioactive