Actinium
Actinium 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.
A stylized shell model. Electrons are quantum objects, not particles following these literal paths. Sizes and motion are illustrative.
86 is the [Rn] core total across six shells.
At a glance
- Atomic number
- 89
- Atomic mass
- 227 u
- Phase
- Solid
- Density
- 10 g/cm³
- Melting point
- 1,500 K
- Boiling point
- 3,500 K
- First ionization energy
- 499 kJ/mol
- Electronegativity
- 1.1
- Electron affinity
- 33.77 kJ/mol
- Molar heat capacity
- 27.2 J/(mol·K)
- Period
- 7
- Appearance
- Unavailable
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.