Helium (He)
Helium (He) is element 2, a noble gas. Atomic mass 4.002602, configuration 1s². Properties, isotopes, oxidation states, uses and history, with an interactive 3D atom model.
Key facts
| Atomic number | 2 |
|---|---|
| Symbol | He |
| Standard atomic weight | 4.002602(2) |
| Category | Noble Gas |
| Group | 18 |
| Period | 1 |
| State at room temperature | Gas |
| Electron configuration | 1s² |
| Valence electrons | 2 |
| Common oxidation states | 0 |
| Common ions | No common ions |
| First ionization energy | 2372 kJ/mol |
| Atomic radius | 31 pm |
| Density | 0.164 g/L |
| Boiling point | -268.93°C |
| Specific heat | 5.193 J/(g·°C) |
Natural isotopes
- He-3: Stable (0.0001%)
- He-4: Stable (99.9999%)
Common uses
- MRI cooling
- Lifting gas (balloons)
- Shielding gas (welding)
Where it matters
- Cryogenics (MRI supermagnets)
- Non-renewable resource conservation
Hazards
- Asphyxiant in confined spaces
History
| Discovered | 1868 (spectral); 1895 (isolated) |
|---|---|
| Discovered by | William Ramsay, Per Teodor Cleve |
| Name | Lockyer & Frankland |