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Protactinium (Pa)
Atomic number 91 · Actinide
| Atomic number | 91 |
|---|---|
| Atomic mass | 231.03588 u |
| Molar mass | 231.03588 g/mol |
| Category | Actinide |
| Group / period / block | — / 7 / f |
| Electron configuration | [Rn] 5f2 6d 7s2 |
| Electrons per shell | 2, 8, 18, 32, 20, 9, 2 |
| Electronegativity (Pauling) | 1.5 |
| Atomic radius | 180.0 pm |
| Density | 15.4 g/cm³ |
| First ionisation energy | 5.89 eV |
| Melting point | 1845.15 K (1572.00 °C) |
| Common oxidation states | +5 |
| Abundance in Earth's crust | 1e-06 ppm |
Uses
Research only
Discovery
1917, Fredrich Soddy, John Cranston, Otto Hahn, Lise Meitner