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 form | metallic 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/cm3 | 10.07 |
| 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 atm | 0.12 |
| Thermal conductivity (W/cm·K) at 25ºC and 1 atm | - |
| Oxidation state | +3 |
| Electron affinity (eV) | 0.35 |
| 1st Ionization potential (eV) | 5.3807 |
