Helium vs Roentgenium
| Property | He Helium | Rg Roentgenium |
|---|---|---|
| Atomic number | 2 | 111 |
| Symbol | He | Rg |
| Name | Helium | Roentgenium |
| Category | noble-gas | transition-metal |
| Standard Atomic Weight | 4.002602 u | 281 u |
| Period | 1 | 7 |
| Group | 18 | 11 |
| Block | s | s |
| Phase at STP | gas | N/A |
| Electron configuration | 1s2 | [Rn] 7s2 5f14 6d9(predicted) |
| Oxidation states | [0] | [-1, 1, 3, 5] |
| Electronegativity (Pauling) | N/A | N/A |
| Electron affinity | -0.5 eV | 1.6 eV |
| Density | 0.1785 kg/m³ | 2.870000e+4 kg/m³ |
| Melting point | -272.2 °C | -273.15 °C |
| Boiling point | -268.93 °C | -273.15 °C |
| Discovery year | 1868 | 1994 |