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.
Experiment with the elements
Helium doesn't form any compounds in our lab yet, but the periodic table sandbox lets you combine dozens of other real elements into real compounds — water, table salt, ammonia and many more — with their true chemical formulas.