2 He 4.003
Helium
Noble Gas
Helium (He) is a chemical element with atomic number 2, classified as a noble gas. At room temperature it is a gas. It was discovered in 1868 by Pierre Janssen, Norman Lockyer.
Properties
- Atomic number
- 2
- Atomic mass
- 4.003 u
- Category
- Noble Gas
- Group
- 18
- Period
- 1
- Block
- s-block
- Electron configuration
- 1s²
- Phase at STP
- Gas
- Density
- 0.1786 g/L
- Melting point
- 0.95 K (-272.2 °C)
- Boiling point
- 4.22 K (-268.9 °C)
- Electronegativity
- —
- Atomic radius
- 31 pm
- Ionization energy
- 24.587 eV
- Discovery
- 1868 · Pierre Janssen, Norman Lockyer
Common uses
Balloons, medical breathing mixtures, cooling superconducting magnets
Did you know?
Second most abundant element in the universe but very rare on Earth.