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