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2
He
4.0026
Helium
Noble gases · Group 18 · Period 1
Atomic properties
| Atomic number | 2 |
|---|---|
| Symbol | He |
| Standard atomic weight | 4.0026 |
| Classification | Noble gases |
| Group | 18 |
| Period | 1 |
| Block | p-block |
| Electron configuration | 1s2 |
| Electronegativity (Pauling) | — |
| Common oxidation states | 0 |
Physical properties
| Phase at 20 °C | Gas |
|---|---|
| Density | 0.0001785 g/cm³ |
| Melting point | -272.20 °C |
| Boiling point | -268.93 °C |
| Discovered | 1868 |
| CAS number | — |