Helium

Noble gas · 4.00260 u · group 18, period 1

Helium · He

Atomic number2

SymbolHe

CategoryNoble gas

Standard stateGas

Group · Period · Block18 · 1 · s

Electron configuration1s2

Atomic mass4.00260 u

Atomic radius140 pm

Protons / Neutrons / Electrons2 / 2 / 2

Shells (e⁻ per shell)2

Electronegativity (Pauling)—

Ionization energy24.587 eV

Electron affinity—

Oxidation states0

Melting point0.9 K · -272.2 °C

Boiling point4.2 K · -268.9 °C

Density1.79e-4 g/cm³

Year discovered1868

CPK color

#D9FFFF

State at room temp (25 °C)

gas

Position