|Type:Noble Gas||Atomic weight:4.00260|
|Density @ 293 K:0.0001787 g/cm3||Atomic volume:27.2 cm3/mol|
Pierre Janssen first obtained evidence of the existence of helium during the solar eclipse of 1868 when he detected an unknown yellow line in the solar spectrum signature. Norman Lockyer and Edward Frankland later confirmed his observations and named the new element helium from the Greek word 'helios', meaning the sun. William Ramsay was first to isolate helium on Earth in 1895 by treating the uranium mineral cleveite with mineral acids.
|State (s, l, g):gas|
|Melting point:0.95 K (-272.2 °C)||Boiling point:4.2 K (-268.9 °C)|
|Specific heat capacity:5.193 J g-1 K-1||Heat of atomization:0 kJ mol-1|
|Heat of fusion:0.0138 kJ mol-1||Heat of vaporization :0.0845 kJ mol-1|
|1st ionization energy:2372.3 kJ mol-1||2nd ionization energy:5250.3 kJ mol-1|
|3rd ionization energy:kJ mol-1||Electron affinity:0 kJ mol-1|
|Minimum oxidation number:0||Maximum oxidation number:0|
|Min. common oxidation no.:0||Max. common oxidation no.:0|
|Electronegativity (Pauling Scale):||Polarizability volume:0.198 Å3|
|Structure:usually hexagonal close-packed (v.high pressure needed to solidify helium)||Color:colorless|
Helium is not known to be toxic.
Helium is a light, odorless, colorless, inert, monatomic gas. It can form diatomic molecules, but only weakly and at temperatures close to absolute zero.
Helium is used for filling balloons (blimps) and for pressurizing liquid fuel rockets.
|Reaction with air:none||Reaction with 6 M HCl:none|
|Reaction with 15 M HNO3:none||Reaction with 6 M NaOH:none|
|Atomic radius:31 pm||Ionic radius (1+ ion):pm|
|Ionic radius (2+ ion):pm||Ionic radius (3+ ion):pm|
|Ionic radius (2- ion):pm||Ionic radius (1- ion):pm|
|Thermal conductivity:0.15 W m-1 K-1||Electrical conductivity:S cm-1|
|Abundance earth's crust:8 parts per billion by weight, 43 parts per billion by moles|
|Abundance solar system:23 % by weight, 7.4 % by moles|
|Cost, pure:$5.2 per 100g|
|Cost, bulk:$ per 100g|
Nearly all the helium remaining on Earth is the result of radioactive decay. The major sources of helium are from natural gas deposits in wells in Texas, Oklahoma and Kansas. Helium is extracted by fractional distillation of the natural gas, which contains up to 7% helium.
Helium has 8 isotopes whose half-lives are known, with mass numbers 3 to 10. Of these two are stable, 3He and 4He. Over 99.999% of naturally occurring helium is in the form of 4He.