Helium vs Thallium
| Property | He Helium | Tl Thallium |
|---|---|---|
| Atomic number | 2 | 81 |
| Symbol | He | Tl |
| Name | Helium | Thallium |
| Category | noble-gas | post-transition-metal |
| Standard Atomic Weight | 4.002602 u | 204.3835 u |
| Period | 1 | 6 |
| Group | 18 | 13 |
| Block | s | p |
| Phase at STP | gas | solid |
| Electron configuration | 1s2 | [Xe]6s24f145d106p1 |
| Oxidation states | [0] | [-5, -2, -1, 1, 2, 3] |
| Electronegativity (Pauling) | N/A | 1.62 |
| Electron affinity | -0.5 eV | 0.377 eV |
| Density | 0.1785 kg/m³ | 1.180000e+4 kg/m³ |
| Melting point | -272.2 °C | 303.85 °C |
| Boiling point | -268.93 °C | 1472.85 °C |
| Discovery year | 1868 | 1861 |