2 He Helium 4.0026
Noble gas
Helium 氦
1s²
- Period 1
- Group 18
- Block s
- Gas
Electron configuration
1s²
Orbital diagram (valence)
1s ↑↓
- Electrons per shell
- 2
- Unpaired electrons
- 0
- Zeff (Slater)
- 1.70
Properties
- Atomic weight
- 4.0026
- Electronegativity (Pauling)
- no data
- First ionization energy
- 2372 kJ/mol
- Electron affinity
- no data
- Covalent radius
- 28 pm
- van der Waals radius
- 140 pm
- Melting point
- 0.95 K
- Boiling point
- 4.22 K
- Density
- 1.785 × 10⁻⁴ g/cm³
- Melting / boiling point
- −272.2 °C / −268.9 °C
- Common oxidation states
- 0
- Discovered
- 1868
Natural isotopes
| Mass number A | Abundance |
|---|---|
| 3He | 1.3 × 10⁻⁴ % |
| 4He | 100.00 % |
Isotope masses: AME2020; abundances: IUPAC/CIAAW representative values.
Emission spectrum
Helium discharge tube · peachy pink
Successive ionization energies
The big jumps appear where core electrons start to be removed. Ionization energies from the NIST Atomic Spectra Database.
Helium in the course
The lessons that discuss this element most (ranked by mentions).
- Radioactive decay Nuclear chemistry
- Real gases Gases
- Molecular-orbital theory Molecular shape
- Nuclear stability and binding energy Nuclear chemistry
- Surfaces and adsorption: counting the molecules that cover a solid Crystals and solids
- Light and spectra: the fingerprints of atoms Atomic structure
- Kinetic theory and the speed distribution Gases
- Mixtures, partial pressures, and effusion Gases
Lab experiments with Helium
Periodic trend
Group 18
Data: PubChem periodic table (public domain); atomic weights are IUPAC abridged standard values; covalent radii from Cordero et al. (2008).