Actinium
Element 89 · Actinide
Actinium is the first member of the actinide series and is intensely radioactive. Pure actinium metal glows with an eerie blue light in the dark because its radiation excites the surrounding air. Like other early actinides it most commonly forms +3 ions. Its most important isotope, actinium-225, has become valuable in targeted alpha therapy for cancer, where its short-range alpha emissions destroy tumor cells while sparing nearby tissue.
Key facts
| Atomic number | 89 |
|---|---|
| Atomic weight | [227] |
| Category | Actinide |
| Group / Period | — / 7 |
| Block | f |
| Electron configuration | [Rn] 6d1 7s2 |
| Common oxidation states | +3 |
| State at STP | Solid |
| Electronegativity | 1.1 |
| Density | 10 g/cm3 |
| Melting point | 1050 °C |
| Boiling point | 3200 °C (estimated) |
Occurrence
Actinium occurs in trace amounts in uranium ores as a decay product in the actinium decay series. It is produced artificially by neutron irradiation of radium-226 for medical use.
Applications
Actinium-225 in targeted alpha therapy for cancer treatment
Neutron source material in research (with beryllium)
Thermoelectric power in specialized space applications (historical)
Common compounds
- Actinium oxide (Ac2O3)
- Actinium fluoride (AcF3)
- Actinium chloride (AcCl3)
Actinium was discovered in 1899 by Andre-Louis Debierne, who separated it from pitchblende residues left over from radium extraction.
Data source: IUPAC standard atomic weights 2021