Helium · He Helium
Cooling medium in cryogenic physics; liquid helium is used in superconducting magnet systems.
- atomic number / Atomic number
- 2
- atomic weight / Atomic mass
- 4.00260 u
- Family/Group
- 18
- Period · Block / Period · Block
- 1 · s
- Category / Category
- rare gas · Noble gas
- State / State
- gaseous state
- Electron configuration
- 1s2
- Oxidation states / Oxidation states
- 0
- Electronegativity / Electronegativity
- not included
- Density / Density
- 0.0001785 g/cm³
- Melting point / Melting point
- 0.95 K
- Boiling point / Boiling point
- 4.22 K
- Atomic radius / Atomic radius
- 140 pm（van der Waals）
- First ionization energy
- 24.587 eV
- Discovery year / Discovery
- 1868
attribute description and data source
properties taken from PubChem periodic table snapshot (2026-10-04). Atomic weights may be reference values or representative isotope masses and cannot be considered exact constants for all samples; density, phase transition points, and phase states depend on temperature, pressure, and allotropes. The solidification of helium requires pressure. Some properties of radioactive and superheavy elements are predicted values, and missing items are marked as not included. Please check the original source and experimental conditions for precise calculations.