Helium
An inert, ultralight noble gas formed in stellar fusion.
Inside the Helium atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Helium atom step by step.
Electron configuration
1s2
A neutral Helium atom has 2 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Physical & atomic properties
- State (room temp)
- Gas
- Melting point
- —
- Boiling point
- 4 K (-269 °C)
- Density
- 0.0001785 g/cm³
- Electronegativity
- —
- Atomic radius
- 31 pm
- 1st ionization energy
- 2372 kJ/mol
- Category
- Noble gases
Discovery & naming
- Discovered
- 1868
- Discovered by
- Pierre Janssen and Norman Lockyer
- Origin of name
- Greek 'helios', the Sun, where it was first detected.
Notable uses
Cryogenics, pressurizing rockets, and lifting balloons and airships.
Where Helium comes from
Big Bang nucleosynthesis
Mostly primordial, formed alongside hydrogen. Stars have been adding more to the total ever since.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 2
- Atomic mass
- 4.0026
- Category
- Noble gases
- Group · Period
- 18 · 1
- Block
- s-block
- Shells
- 2