Hydrogen vs Helium
Pick up to 3 elements and see how they stack up.
| Property | Hydrogen | Helium |
|---|---|---|
| Atomic number | 1 | 2 |
| Atomic mass | 1.008 | 4.0026 |
| Electronegativity | 2.2 | — |
| Melting point | 13.99 K (-259.2 °C) | 0.95 K (-272.2 °C) |
| Boiling point | 20.27 K (-252.9 °C) | 4.22 K (-268.9 °C) |
| Density | 0.09 g/L | 0.179 g/L |
| Atomic radius | 120 pm | 140 pm |
| Ionization energy | 13.598 eV | 24.587 eV |
| Discovered | 1766 | 1868 |
| Category | Reactive nonmetal | Noble gas |
| State at room temp. | Gas | Gas |
| Block | s | s |
| Group | 1 | 18 |
| Period | 1 | 1 |
| Valence electrons | 1 | 2 |
| Common charges | +1, −1 | 0 |
| Electron configuration | 1s1 | 1s2 |