Element 2 · Noble gas
Helium (He) — Element 2
Greek helios — the Sun
Helium (He) is a noble gas in Period 1, Group 18 of the periodic table with atomic number 2, standard atomic weight 4.0026 u, and ground-state electron configuration 1s². At standard temperature and pressure it is classified as a gas with 0 valence electrons and common oxidation states 0.
Cryogenics, balloons, MRI magnets
What are the atomic properties and physical constants of Helium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 2
- Standard atomic mass
- 4.0026 u
- Chemical family
- Noble gas
- Ground-state configuration
- 1s²
- Electrons per shell
- 2
- Valence electrons
- 0
- Common ion charges / oxidation states
- 0
- Phase at STP
- Gas
- Pauling electronegativity
- —
- First ionization energy
- 2,372 kJ/mol
- Atomic radius
- 31 pm
- Melting point
- —
- Boiling point
- -269 °C
- Discovery year
- 1868
- Table coordinate
- Period 1, Group 18
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Helium’s shells?
A neutral Helium atom contains 2 electrons distributed across 1 occupied principal energy shell (1s²). The table below compares Helium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in He | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
Frequently Asked Questions about Helium (He)
What is the atomic mass and atomic number of Helium (He)?
Helium (He) has atomic number Z = 2 (2 protons in its nucleus) and an IUPAC standard atomic weight of 4.0026 u. It sits in Period 1, Group 18 and is classified as a noble gas.
What is the ground-state electron configuration of Helium?
The neutral ground-state electron configuration of Helium (Z = 2) is 1s². Across its 1 occupied principal shells (n = 1 to n = 1), the electrons per shell are 2, with 0 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Helium?
Helium commonly forms 0 oxidation states or ion charges in compounds. Its Pauling electronegativity is — and its first ionization energy is 2,372 kJ/mol.
When was Helium discovered and what is it used for?
Helium was discovered in 1868 (Greek helios — the Sun). Cryogenics, balloons, MRI magnets
How does Helium compare to neighboring elements?
Other noble gas elements: