89Ac[227]
Actinium (Ac)
Element 89 · Actinide
Actinium (Ac) is a chemical element with atomic number 89. It is classified as an actinide in period 7 of the periodic table (the f-block). Its most stable known isotope has mass number 227 and its ground-state electron configuration is [Rn] 6d¹ 7s².
Actinium facts
| Atomic number (Z) | 89 |
|---|---|
| Symbol | Ac |
| Mass number of most stable isotope | [227] |
| Category | Actinide |
| Group | — (f-block) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 6d¹ 7s² |
| Electronegativity (Pauling) | 1.1 |
| State at 20 °C | Solid |
| Protons / electrons | 89 / 89 |
| Neutrons (most common isotope, approx.) | 138 |
| Molar mass | 227 g/mol |