Helium (2)

Helium is one of the so-called noble gases. Helium gas is an unreactive, colorless, and odorless monoatomic gas. Helium is available in pressurized tanks.

Helium is the second most abundant element in the universe after hydrogen. α-particles are doubly ionized helium atoms, He2+.

Helium is used in lighter than air balloons and while heavier than hydrogen, is... far safer since helium does not burn. Speaking after breathing an atmosphere rich in helium results in a squeaky voice (don't try it- may lead to asphyxiation).

Helium is present in the atmosphere at about 0.0005% (1 part in 200000) by volume and is an important component within hydrocarbon gases in the USA. Its origin in these gases is traced to the decay of radioactive elements in rocks.

 

•Name: Helium
•Symbol: He
•Atomic number: 2
•Atomic weight: 4.002602 (2) [see notes g r]
•Standard state: gas at 298 K
•CAS Registry ID: 7440-59-7
•Group (column) in periodic table: 18
•Group name: Noble gas
•Period (row) in periodic table: 1
•Block in periodic table: p-block
•Color: colorless
•Classification: Non-metallic

Historical information

Helium was discovered by Sir William Ramsay and independently by N. A. Langley and P. T. Cleve at 1895 in London, England and Uppsala, Sweden. Origin of name: from the Greek word "helios" meaning "sun." A French astronomer, Pierre-Jules-César Janssen (1824-1907), first obtained evidence for the existence of helium during the solar eclipse of 1868 in India when he detected a new yellow line (587.49 nm) in the solar spectrum very close to the yellow sodium D-line. It was not possible to produce this line in the laboratory. Sir Norman Lockyer (1836-1920), an English astronomer, recognized that no known element at that time gave this line and named the element helium for the sun. For many years helium was regarded as an element that might exist on the sun although it was unknown on the Earth. Spectroscopists at the time doubted the results concerning helium. However the claims initiated a search for the new element on planet earth. In 1895, Sir William Ramsay discovered helium after treating cleveite, a uranium mineral, with mineral acids. Ramsey sent samples of the gas to Sir William Crookes and Sir Norman Lockyer who identified helium. It was discovered independently in clevite by Cleve and Langley at about the same time. Lockyer and Professor Edward Frankland suggested the name helium.

Physical properties

•Melting point: 0.95 [or -272.2 °C (-458 °F)] K
•Boiling point: 4.22 [or -268.93 °C (-452.07 °F)] K
•Density of solid: 214 kg m-3

Orbital properties

•Ground state electron configuration: 1s2
•Shell structure: 2
•Term symbol: 1S0

Isolation

There is very little helium on earth as nearly all present during and immediately after the earth's formation has long since been lost as it is so light. Just about all the helium remaining on the planet is the result of radioactive decay. While there is some helium in the atmosphere, currently its isolation from that source by liquefaction and separation of air is not normally economic. This is because it is easier, and cheaper, to isolate the gas from certain natural gases. Concentrations of helium in natural gas in the USA are as high as 7% and other good sources include natural gas from some sources in Poland. It is isolable from these gases by liquefaction and separation of from the natural gas. This would not normally be carried out in the laboratory and helium is available commercially in cylinders under pressure.