He
Helium
Element 2 · Noble gas
Helium (He)
Helium is a colourless, inert noble gas, the second most plentiful element in the universe. No other substance boils at a lower temperature.
- Noble gas
- Period 1
- Group 18
- s-block
- gas at room temperature
Key properties
- Atomic mass
- 4.0026
- u
- Electron configuration
- 1s2
- Melting point
- -272.2 °C
- 0.95 K
- Boiling point
- -268.9 °C
- 4.22 K
- Density
- 0.1785 g/L
- Electronegativity
- —
- Atomic radius
- 140 pm
- van der Waals
- 1st ionisation energy
- 24.587 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about helium
- 01
Helium is the only element that cannot be frozen at normal pressure — it stays liquid down to absolute zero.
- 02
Almost all of Earth’s helium comes from radioactive alpha decay deep underground and is trapped with natural gas.
- 03
Below 2.17 K liquid helium becomes a superfluid that can creep up and over the walls of its container.
Applications
What is helium used for?
- Cooling MRI superconducting magnets
- Balloons and airships
- Shielding gas for welding
- Breathing mixtures for deep-sea divers
History
Discovery & name origin
Discovered by
Year
Where
Observed in the solar spectrum
Name origin
Greek helios, “sun” — it was spotted in sunlight 27 years before it was found on Earth.
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 2
- Atomic mass
- 4.0026 u
- Group
- 18
- Period
- 1
- Block
- s-block
- Electron configuration
- 1s2
- Full configuration
- 1s2
- Electrons per shell
- 2
- Electronegativity (Pauling)
- —
- Electron affinity
- —
- Atomic radius (van der Waals)
- 140 pm
- Stable isotopes
- 2
Oxidation states
Highlighted: common oxidation states (0).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st2,372.3
- 2nd5,250.5
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Gas
- Melting point
- 0.95 K · -272.2 °C · -458 °F
- Boiling point
- 4.22 K · -268.9 °C · -452.1 °F
- Density
- 0.1785 g/L
- Molar heat capacity
- —
- Appearance
- Colourless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Helium questions
What is He on the periodic table?
He is the symbol for helium, element 2 on the periodic table. It sits in group 18, period 1, in the noble gas category, and has an atomic mass of 4.0026.
What is the atomic number of helium?
Helium has atomic number 2, so every helium atom has 2 protons in its nucleus. Its symbol is He and its atomic mass is 4.0026.
Who discovered helium?
Helium was discovered by Pierre Janssen and Norman Lockyer in 1868 (Observed in the solar spectrum). The name comes from Greek helios, “sun” — it was spotted in sunlight 27 years before it was found on Earth.
What is helium used for?
Helium is used for: cooling MRI superconducting magnets; balloons and airships; shielding gas for welding; breathing mixtures for deep-sea divers.
Is helium a metal?
No. Helium is classed as a noble gas.
What is the electron configuration of helium?
The electron configuration of helium is 1s2. Its 2 electrons are arranged in shells as 2.