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Helium

He
Atomic Number:
Atomic Weight:
Element Type:
Crystal Structure:
Melting Point:
Boiling Point:
Critical Temp:
Atomic Radius:
Covalent Radius:
Electronegativity:
2
4.00260
Noble Gas
Hexagonal
-268.93°C = -452.074°F = 4.22 K
-267.96°C = -450.328°F = 5.19 K
°C = °F = K
0.49Å (Å = Angstrom = 10-10 m)
0.93 Å

Discovery

(Gr. helios, the sun). Janssen obtained the first evidence of helium during the solareclipse of 1868 when he detected a new line in the solar spectrum. Lockyer and Franklandsuggested the name helium for the new element. In 1895 Ramsay discovered helium in theuranium mineral clevite while it was independently discovered in cleveite by the Swedishchemists Cleve and Langlet at about the same time. Rutherford and Royds in 1907demonstrated that alpha particles are helium nuclei.

Sources

Except for hydrogen, helium is the mostabundant element found through out the universe. Helium is extracted from natural gas. Infact, all natural gas contains at least trace quantities of helium.

It has been detected spectroscopically in great abundance, especially in the hotterstars, and it is an important component in both the proton-proton reaction and the carboncycle, which account for the energy of the sun and stars.

The fusion of hydrogen into helium provides the energy of the hydrogen bomb. The heliumcontent of the atmosphere is about 1 part in 200,000. While it is present in variousradioactive minerals as a decay product, the bulk of the Free World's supply is obtainedfrom wells in Texas, Oklahoma, and Kansas. The only known helium extraction plants,outside the United States, in 1984 were in Eastern Europe (Poland), the USSR, and a few in India.

Uses

Helium is widely used in cryogenic research because its boiling point is near absolute zero. It is used in the study of superconductivity, as an inert gas shield for arc welding, as a protective gas in growing silicon and germanium crystals and producing titanium and zirconium, for pressuring liquid fuel rockets, for use in magnetic resonance imaging (MRI), as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels. A mixture of helium and oxygen is used as an artificial atmosphere for divers and others working under pressure. Helium is used for filling balloons and blimps.


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