91Pa231.04
Protactinium (Pa)
Element 91 · Actinide
Protactinium (Pa) is a chemical element with atomic number 91. It is classified as an actinide in period 7 of the periodic table (the f-block). Its standard atomic weight is 231.04 u and its ground-state electron configuration is [Rn] 5f² 6d¹ 7s².
Protactinium facts
| Atomic number (Z) | 91 |
|---|---|
| Symbol | Pa |
| Standard atomic weight | 231.04 u |
| Category | Actinide |
| Group | — (f-block) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 5f² 6d¹ 7s² |
| Electronegativity (Pauling) | 1.5 |
| State at 20 °C | Solid |
| Protons / electrons | 91 / 91 |
| Neutrons (most common isotope, approx.) | 140 |
| Molar mass | 231.04 g/mol |