61Pm[145]
Promethium (Pm)
Element 61 · Lanthanide
Promethium (Pm) is a chemical element with atomic number 61. It is classified as a lanthanide in period 6 of the periodic table (the f-block). Its most stable known isotope has mass number 145 and its ground-state electron configuration is [Xe] 4f⁵ 6s².
Promethium facts
| Atomic number (Z) | 61 |
|---|---|
| Symbol | Pm |
| Mass number of most stable isotope | [145] |
| Category | Lanthanide |
| Group | — (f-block) |
| Period | 6 |
| Block | f-block |
| Electron configuration | [Xe] 4f⁵ 6s² |
| Electronegativity (Pauling) | 1.13 |
| State at 20 °C | Solid |
| Protons / electrons | 61 / 61 |
| Neutrons (most common isotope, approx.) | 84 |
| Molar mass | 145 g/mol |