Electronic data		Thermal data		Steric data
Shells: 2 Orbitals: 1s2 Electronegativity: 5.5, -- 1. Ionization potential: 24.5874 eV 2. Ionization potential: 54.416 eV 3. Ionization potential: -- eV Oxidation states: 0 Electrical conductivity: --		Melting point: -272.2 °C @ 26 atmos. Boiling point: -268.934 °C Specific heat: 5.193 J/gK Heat of fusion: -- kJ/mol Heat of vaporization: 0.0845 kJ/mol Thermal conductivity: 0.00152 W/cmK		Atomic radius: 0.49 Å Ionic radius: -- Å () Covalent radius: 0.93 Å Atomic volume: 19.5 cm³/mol Density (293 K): 0.0001787 g/cm³ Crystal structure: Hexagonal

Nuclide	Abundance [%]	Mass	Spin	Halflife	Decay mode	Decay tree
3He	0.00013	3.016	1/2	--	stable	--
4He	99.9999	4.0026	0	--	stable	--

Legend

Name origin:	Greek: hêlios (sun)
Description:	Light, odorless, colorless, tasteless inert gas. Second most abundant element in the universe. Sixth most abundant in the earth's atmosphere.
Discovered by:	Sir William Ramsey, Nils Langet, P.T.Cleve
Year:	1895
Place:	Scotland/Sweden
Sources:	Found in natural gas deposits & in the air (5 parts per billion) Constantly lost to space; replenished by radioactive decay (alpha particles).
Use(s):	Used in balloons, deep sea diving & welding. Also used in very low temperature research.