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
Documented element sampleA gas discharge tube shaped like the symbol He; the excited helium glows and makes the otherwise invisible gas visible.
Image credit: User:Pslawinski
Auto-oriented, limited to 1600 × 1200 pixels and re-encoded as WebP; the subject was not altered.
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
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.
Where Helium sits among the 118 elements
The table compares the reported values for Helium with every other element that carries the same value in the snapshot. A rank is not a judgement, it is orientation: it says how unusual this value is across the periodic table.
| Value | Helium | Position in the data set |
|---|---|---|
| Melting point | 0.95 K | Rank 103 of 103 elements with a reported value. Highest: Carbon. |
| Boiling point | 4.22 K | Rank 93 of 93 elements with a reported value. Highest: Rhenium. |
| Density | 0 g/cm³ | Rank 95 of 96 elements with a reported value. Highest: Osmium. |
| Ionisation energy | 24.587 eV | Rank 1 of 102 elements with a reported value. Highest: Helium. |
All values and ranks come from the PubChem Periodic Table snapshot, retrieved on 2026-07-15. Elements without a reported value are excluded, so the population differs per row.
The neighbours of Helium in the periodic table
- Place in the table
- Group 18, period 1, S block. Classified as noble gas, gaseous at standard conditions.
- Direct neighbours
- Atomic number 2. Preceded by Hydrogen, followed by Lithium.
- Same group
- Same number of outer electrons, and therefore similar reactivity to Neon, Argon, Krypton, Xenon, Radon, Oganesson.
- Discovery
- Recorded in the snapshot as: 1868. Who, where and under what circumstances is not part of that record, so this page carries the sourced year and no discovery narrative.
- Oxidation states
- 0. They follow from the electron configuration 1s2 and indicate which compounds to expect.
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