Promethium vs Fermium
| Property | Pm Promethium | Fm Fermium |
|---|---|---|
| Atomic number | 61 | 100 |
| Symbol | Pm | Fm |
| Name | Promethium | Fermium |
| Category | lanthanide | actinide |
| Standard Atomic Weight | 145 u | 257 u |
| Period | 6 | 7 |
| Group | N/A | N/A |
| Block | s | s |
| Phase at STP | solid | solid |
| Electron configuration | [Xe]6s24f5 | [Rn] 5f12 7s2 |
| Oxidation states | [2, 3] | [2, 3] |
| Electronegativity (Pauling) | N/A | 1.3 |
| Electron affinity | 0.129 eV | 0.339 eV |
| Density | 7260 kg/m³ | 9700 kg/m³ |
| Melting point | 1041.85 °C | 1526.85 °C |
| Boiling point | 2999.85 °C | -273.15 °C |
| Discovery year | 1902 | 1952 |