Protactinium (Pa)
Protactinium (Pa) is element 91, an actinide. Atomic mass 231.03588, configuration [Rn] 5f² 6d¹ 7s². Properties, isotopes, oxidation states, uses and history, with an interactive 3D atom model.
Key facts
| Atomic number | 91 |
|---|---|
| Symbol | Pa |
| Standard atomic weight | 231.03588(1) |
| Category | Actinide |
| Period | 7 |
| State at room temperature | Solid |
| Electron configuration | [Rn] 5f² 6d¹ 7s² |
| Valence electrons | 2 (Variable) |
| Common oxidation states | +5 |
| Common ions | No common ions |
| Electronegativity (Pauling) | 1.5 |
| First ionization energy | 568 kJ/mol |
| Atomic radius | 180 pm |
| Density | 15.4 g/cm³ |
| Melting point | 1570°C |
| Boiling point | ~4000°C |
Common uses
- Research only
Where it matters
- Radiometric dating (Protactinium-Thorium dating)
Hazards
- Highly toxic and radioactive
History
| Discovered | 1913 |
|---|---|
| Discovered by | Fajans & Göhring |
| Name | Greek protos (first) + actinium |