Helium (He)
Element 2 · Noble gas · atomic mass 4.0026 u · group 18, period 1
Electron shells: 2
Helium is an inert noble gas with the lowest boiling point of any element, at just 4.2 K. It is produced underground by the radioactive decay of heavy elements and collected from natural gas wells.
Helium was found in the Sun's spectrum 27 years before anyone found it on Earth.
- Atomic number
- 2
- Atomic mass
- 4.0026 u
- Electron configuration
- 1s²
- Group · period · block
- 18 · 1 · s
- Oxidation states
- 0
- Electronegativity
- Not measured
- Melting point
- -272 °C
- Boiling point
- -269 °C
- Density
- 0.0001785 g/cm³
- State at 20 °C
- Gas
- Appearance
- Colourless, odourless gas
- Discovered
- Pierre Janssen and Norman Lockyer, 1868
2 protons, and 2 electrons when neutral
IUPAC standard atomic weight
Noble gases
What Helium is used for
- Cooling MRI superconducting magnets
- Lifting gas for balloons and airships
- Leak detection
- Protective atmosphere for welding
Atomic structure of Helium
A neutral helium atom has 2 protons and 2 electrons. Its most common isotope carries about 2 neutrons, which is where the mass number 4 comes from. Change the neutron count and you have a different isotope of helium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2. In orbital notation that is 1s², leaving 2 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Helium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Helium sits in the periodic table
Discovery and naming
Helium was discovered by Pierre Janssen and Norman Lockyer in 1868. Its name comes from Greek helios, "sun".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Helium?
The standard atomic weight of Helium is 4.0026 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Helium have?
Helium has 2 protons, because the atomic number is the proton count and that is what makes an atom Helium at all. A neutral Helium atom has the same number of electrons, 2. The neutron count varies by isotope; the most common one has about 2, since 4 − 2 = 2.
What is the electron configuration of Helium?
The electron configuration of Helium is 1s². Its electrons are arranged 2 across 1 shell.
Is Helium a metal?
No. Helium is classified as a noble gas, on the right-hand side of the table where elements gain or share electrons rather than losing them.
What group and period is Helium in?
Helium is in group 18 (the noble gases), period 1, in the s-block. The group is its column and the period is its row.
What is the melting point of Helium?
Helium melts at -272 °C and boils at -269 °C. That puts it in the gases at everyday temperatures.
What is Helium used for?
Cooling MRI superconducting magnets, Lifting gas for balloons and airships, Leak detection, Protective atmosphere for welding. Helium is an inert noble gas with the lowest boiling point of any element, at just 4.2 K.
Who discovered Helium, and where does its name come from?
Helium (He) was discovered by Pierre Janssen and Norman Lockyer in 1868. The name comes from Greek helios, "sun".