Helium

General:

Name:Helium Symbol:He
Type:Noble Gas Atomic weight:4.00260
Density @ 293 K:0.0001787 g/cm3 Atomic volume:27.2 cm3/mol
Discovered:

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.

States

State (s, l, g):gas
Melting point:0.95 K (-272.2 °C) Boiling point:4.2 K (-268.9 °C)

Energies

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

Oxidation & Electrons

Shells:2 Electron configuration:1s2
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

Appearance & Characteristics

Structure:usually hexagonal close-packed (v.high pressure needed to solidify helium) Color:colorless
Hardness:mohs
Harmful effects:

Helium is not known to be toxic.
 

Characteristics:

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 has the lowest melting point of any element and its boiling point is close to absolute zero.

Unlike any other element, helium does not solidify but remains a liquid down to absolute zero (0 K) under ordinary pressures.

The voice of someone who has inhaled helium temporarily sounds high-pitched.


Uses:

Helium is used for filling balloons (blimps) and for pressurizing liquid fuel rockets.

Mixtures of helium and oxygen are used as an artificial 'air' for divers and others working under pressure. Helium is used instead of the nitrogen in normal air because, after a long dive, helium leaves the body faster than nitrogen, allowing faster decompression.

Helium is used as a gas shield in the vicinity of arc welding and in cryogenics, preventing, for example, any reaction of hot metal welds with oxygen. The gas is used in the semi-condictor industry to provide an inert atmosphere for growing silicon and germanium crystals. It is also used as a high temperature gas in titanium and zirconium production, and as a carrier gas in in gas chromatography.

By virtue of its very low temperature, liquid helium is used to produce superconductivity in some ordinary metals.

Reactions

Reaction with air:none Reaction with 6 M HCl:none
Reaction with 15 M HNO3:none Reaction with 6 M NaOH:none

Compounds

Oxide(s):none Chloride(s):none
Hydride(s):none

Radius

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

Conductivity

Thermal conductivity:0.15 W m-1 K-1 Electrical conductivity:S cm-1

Abundance & Isotopes

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
Source:

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.

Isotopes:

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.

Other

Other:

 

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