Ac
Actinium
Actinium is a chemical element with the symbol Ac and atomic number 89. It has a mass number of 227, sits in period 7 of the f-block, and is classified as an actinide.
Properties
| Symbol | Ac |
|---|---|
| Atomic number | 89 |
| Mass number | 227 |
| Category | Actinide |
| Group | f-block — no group |
| Period | 7 |
| Electron configuration | [Rn] 5f1 7s2 |
| Outer-shell electrons | 2 |
The figure of 227 is a mass number rather than a measured atomic weight, because this element has no stable isotope.
Calculate with actinium
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
Atomic weights are the IUPAC 2021 standard values, abridged to the conventional five significant figures. Group, period, category and electron configuration are derived from the atomic number rather than stored, so they cannot drift out of step with it.