Periodic Table of Elements




Actinium was discovered by Andr-Louis Debierne, a French chemist in 1899.

Name: Actinium
Symbol: Ac
Atomic number: 89
Atomic weight: 227.03
State: solid
Group, period, block: n/a, 7, f
Color: silvery-white
Classification: actinide
Electron configuration: 6d1 7s2

Physical properties

Density: 10 g/cm-3
Melting point: 1323 K,1050 C,1922 F
Boiling point: 3471 K,3198 C,5788 F

Atomic properties

Oxidation states: 3
Electronegativity: 1.1 (Pauling scale)
Ionization energies: 1st: 499 kJmol-1
Covalent radius: 215 pm
Van der Waals radius: no data
  • Ac
  • Electron Configuration


Actinium has no stable isotopes. There are 31 known isotopes, from 206Ac to 236Ac, and 2 isomers.