Helium

Atomic number

2

Atomic mass (u)

4.00260

Category

Noble gas

Standard state

Gas

Melting point

-272.2 °C (0.95 K)

Boiling point

-268.93 °C (4.22 K)

Density (g/cm³)

0.0001785

Electronegativity (Pauling)

Not reported in this source

Electron configuration

1s2

Oxidation states

0

Atomic radius (pm)

140

First ionization energy (eV)

24.587

Discovery & recognition

Discovery year / period (PubChem)

1868

Discovery credited to (RSC)

Sir William Ramsay in London, and independently by Per Teodor Cleve and Nils Abraham Langlet in Uppsala, Sweden

Date or period recorded by RSC

1895

Discovery place

Not supplied in the structured record; see the RSC history source.

An ancient date does not identify a first human discovery. Different references may date observation, isolation and formal recognition differently.

Natural occurrence & production

The creation of an element’s nuclei and its concentration into terrestrial deposits are different processes. The occurrence note below concerns its presence or production on Earth; it is not a complete account of nucleosynthesis.

“After hydrogen, helium is the second most abundant element in the universe.”

Royal Society of Chemistry · occurrence excerpt ↗

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Reference values are not product specifications. Blank values have not been estimated. For superheavy elements, some properties and family assignments are theoretical or incompletely measured.