Chemical element · Atomic number 2
Helium
Helium in the periodic table: atomic number 2, electron configuration, atomic mass, physical data, oxidation states, media credit and visible sources.
Noble gas
gaseous
4.00260 u
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Atomic classification
Shell occupancy
Helium in the Bohr shell model
This shows the electron distribution of the neutral atom in a simplified shell model.
- K · n=1
- 2 electrons
- Electron configuration
- 1s2
- Electrons per shell
- 2
- Group
- 18
- Period
- 1
- Block
- S
- Element category
- Noble gas
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Physical and chemical properties
- Atomic mass
- 4.00260 u
- Standard state
- gaseous
- Density
- 0.0001785 g/cm³
- Melting point
- 0.95 K
- Boiling point
- 4.22 K
- Electronegativity
- not reported
- First ionisation energy
- 24.587 eV
- Oxidation states
- 0
- Discovery
- 1868
Safety and periodic classification
Safety
Safe handling cannot be inferred from Helium's position in the periodic table alone. Laboratory, classroom and disposal decisions must follow the documentation for the exact material and its safety data sheet.
Position and comparison
Helium is in period 1, group 18 and the S block. Its direct neighbours by atomic number are Hydrogen and Lithium. The snapshot does not report a Pauling electronegativity. Periodic trends are compared only through the separately sourced neighbouring values.
Sources and scope
PubChem attributes element data to sources including IUPAC, NIST and IAEA. Quanta stores the referenced snapshot locally and leaves unknown values unavailable.