Helium vs Cesium
| Property | He Helium | Cs Cesium |
|---|---|---|
| Atomic number | 2 | 55 |
| Symbol | He | Cs |
| Name | Helium | Cesium |
| Category | noble-gas | alkali-metal |
| Standard Atomic Weight | 4.002602 u | 132.905452 u |
| Period | 1 | 6 |
| Group | 18 | 1 |
| Block | s | s |
| Phase at STP | gas | solid |
| Electron configuration | 1s2 | [Xe]6s1 |
| Oxidation states | [0] | [-1, 1] |
| Electronegativity (Pauling) | N/A | 0.79 |
| Electron affinity | -0.5 eV | 0.4716 eV |
| Density | 0.1785 kg/m³ | 1930 kg/m³ |
| Melting point | -272.2 °C | 28.44 °C |
| Boiling point | -268.93 °C | 670.85 °C |
| Discovery year | 1868 | 1860 |