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
- None at 1 atmHelium does not freeze at atmospheric pressure - it stays liquid to absolute zero, and solidifies only above roughly 2.5 MPa (about 0.95 K).
- Boiling point
- 4.22 K (-268.93 °C)
- 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
Frequently asked questions
- Is helium a metal?
- No. Helium is a nonmetal, classified as a noble gas on the periodic table.
- How many protons does helium have?
- Helium has 2 protons. Its atomic number is 2, which is also the number of electrons in a neutral atom of helium.
- What group and period is helium in?
- Helium is in group 18 and period 1 of the periodic table, in the s-block.
- What is the atomic mass of helium?
- The atomic mass of helium is 4.0026 u (unified atomic mass units).
Keep exploring
Helium's row is on the printable element property sheet, and its tile is on the periodic table wall chart - the same numbers as above, laid out for A4 or A3 paper.