Element 2
Helium (He)
Helium (He) is element 2 of the periodic table, a noble gas in period 1, group 18 (s-block) with an atomic mass of 4.0026 and is a gas at standard conditions.
At a glance
- Atomic number
- 2
- Symbol
- He
- Atomic mass
- 4.0026 u
- Category
- Noble gases
- Period
- 1
- Group
- 18
- Block
- s-block
- Phase at STP
- gas
Electron structure
- Electron configuration
- 1s2
- Shorthand configuration
- 1s2
- Electrons per shell
- 2
- Oxidation states
- 0
Physical properties
- Melting point
- 0.95 K
- Boiling point
- 4.22 K
- Density
- 0.0001785 g/cm3
- Phase
- gas
Atomic properties
- Atomic radius
- 31 pm
- Covalent radius
- 28 pm
- Van der Waals radius
- 140 pm
- First ionization energy
- 2372 kJ/mol
- Electron affinity
- 0 kJ/mol
Notable isotopes
| Isotope | Mass | Abundance | Stability |
|---|---|---|---|
| He-4 | 4.0026 | 99.99% | Stable |
Common uses
- Balloons
- Cryogenics
- MRI machines
- Welding
Discovery
- Year
- 1868
- Discovered by
- Pierre Janssen, Joseph Lockyer
- Country
- France/England