Rare in nature, actinium is a metal formed by the decay of other radioactive elements. Its atoms are unstable and decay to form the elements calcium and radon. Actinium is found in minute quantities in uranium ores, such as tobernite, and has limited applications. Its isotopes are used in radiotherapy to treat cancer.

Summary of properties (Ac)

Atomic weight[227]
Discoverer (year)Debierne, André (1899)
Natural formmetallic solid (face centered cubic)
Electron configuration[Rn] 6d1 7s2
Melting point (ºC)1050
Boiling point (ºC)3200
Abundance in earth's crust (ppm)<0.001
Isotope (abundance)
Density g/cm310.07
Van der Waals radius (pm)247
Covalent radius (pm)201
Electronegativity (Pauling)1.1
Vaporization enthalpy (kJ/mol)418.00
Enthalpy of fusion (kJ/mol)14.20
Specific heat capacity (J/g·K) at 25ºC and 1 atm0.12
Thermal conductivity (W/cm·K) at 25ºC and 1 atm-
Oxidation state+3
Electron affinity (eV)0.35
1st Ionization potential (eV)5.3807

Back to the Periodic Table of the Elements.