Compare Hydrogen vs Helium
Comparing Hydrogen (H) and Helium (He). Atomic numbers 1 and 2 with atomic masses 1.008 u and 4.003 u, classified as nonmetal and noble gas. Below: a side-by-side comparison of their physical, atomic, electron-configuration and historical properties, including density, melting and boiling points, ionization energies, oxidation states and discovery history.
Periodic properties of the elements
| Hydrogen | Helium | |
|---|---|---|
| Symbol | H | He |
| Atomic number | 1 | 2 |
| Group | 1 | 18 |
| Period | 1 | 1 |
| Block | s | s |
| Element category | Nonmetal | Noble Gas |
Physical properties
| Hydrogen | Helium | |
|---|---|---|
| Phase at STP | Gas | Gas |
| Density | 0.08988 g/cm3 | 0.1786 g/cm3 |
| Atomic weight | 1.0079 u | 4.0026 u |
| Melting point | 13.99 K -259.16 °C -434.488 °F | 0.95 K -272.2 °C -457.96 °F |
| Boiling point | 20.271 K -252.879 °C -423.1822 °F | 4.222 K -268.928 °C -452.0704 °F |
Atomic properties
| Hydrogen | Helium | |
|---|---|---|
| Electronegativity (Pauling Scale) | 2.2 | 0 |
| Electron affinity | 72.769 kJ/mol | -48 kJ/mol |
| Oxidation states | −1, +1 (an amphoteric oxide) | 0 |
| Ionization energies |
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Electron configuration
| Hydrogen | Helium | |
|---|---|---|
| Shorthand configuration | 1s1 | 1s2 |
| Full configuration | 1s1 | 1s2 |
| Electrons per shell | 1 | 2 |
History
| Hydrogen | Helium | |
|---|---|---|
| Discovery | Henry Cavendish (1766) | Pierre Janssen, Norman Lockyer (1868) |
| First isolation | Henry Cavendish (1766) | William Ramsay, Per Teodor Cleve, Abraham Langlet (1895) |
| Named by | Antoine Lavoisier (1783) | Edward Frankland, Norman Lockyer (1868) |