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91
Pa
231.04
Protactinium
Actinides · Group 5 · Period 6–7 (f)
Atomic properties
| Atomic number | 91 |
|---|---|
| Symbol | Pa |
| Standard atomic weight | 231.04 |
| Classification | Actinides |
| Group | f-block series |
| Period | 7 |
| Block | f-block (actinide) |
| Electron configuration | [Rn] 5f2 6d1 7s2 |
| Electronegativity (Pauling) | 1.50 |
| Common oxidation states | +5, +4 |
Physical properties
| Phase at 20 °C | Solid |
|---|---|
| Density | 15.37 g/cm³ |
| Melting point | 1568 °C |
| Boiling point | 4027 °C |
| Discovered | 1913 |
| CAS number | — |