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Helium

Non-Metalgaseous
Symbol: He
Atomic number: 2
Atomic mass: 4.002602
Group: Noble Gas
CAS-number: 7440-59-7

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Physical data
Isotopes
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Physical data

Electronic dataThermal dataSteric 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
hexagonal

Isotopes

NuclideAbundance [%]MassSpinHalflifeDecay modeDecay tree
3He 0.00013 3.016 1/2 -- --
4He 99.9999 4.0026 0 -- --

Other info

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 and in the air (5 parts per billion). It is constantly lost to space and then replenished by radioactive decay (alpha particles).
Use(s):Used in balloons, deep sea diving and in welding. Also used in very low temperature research.