Uranium ore
Helium is an inert, monoatomic,lightest, colorless noble gas element. In 1868, Lockyer studied the spectrum of the sun during the total eclipse. From his investigations, he concluded that a new element was present in the atmosphere of the Sun. He called this new element as Helium (In Greek, Helos means the sun). Later on, in 1895, Ramsay heated Clevite, a mineral of uranium and obtained the same gas, i. e. helium. Thus, the gas is present both in the atmosphere of the sun as well as on the earth.
Helium presence was discovered in the atmosphere of the sun
Helium is second most abundant element in the universe. On earth the occurrence of helium is very rare, it is obtained as a result of radioactive decay of minerals of uranium, thorium, pitchblende etc. There are eight known isotopes of helium, but only helium–3 and helium–4 are stable. The most common isotope of helium is helium–4( radio decay element). Helium will remain liquid down to absolute zero at normal pressures. .Helium is commercially extracted by fractional distillation of natural gas . Commercially it is produced either as a liquid or gas.
Helium has the lowest boiling point and melting point. It crystallizes in a hexagonal closed packed (FCC) structure. Liquid helium on further cooling changes to another allotrope of Helium, called Helium(II), with negligible viscosity, fluid with low viscosity known is as superfluid. Therefore, when kept in a container Helium even goes uphill and flows out of the vessel.Clever engineering tricks such as a constriction etc., have to be made to the dewar holding liquid helium, so that this loss is prevented.
Helium balloon
Helium balloons fly, because helium is lighter than air. Helium weighs about 0.1785 grams per liter
Uses
- It is used in gas–cooled atomic reactors as a heat transfer gas.
- It is used for filling observation–balloons, due to its non–inflammability. Its lifting power is 92% of hydrogen gas.
- It is used as a cryogenic fluid (b.p. 4.2 K) helping to produce and maintain the lowest temperature for scientific research.
- A mixture of oxygen and helium is used as a respiration mixture by sea–divers. Since, helium does not dissolve in blood, hence it does not cause a painful sensation called bends, when the sea-diver comes out of water. Nitrogen gas being relatively more soluble in blood, cannot be used for the purpose.
- It is used for providing an inert atmosphere.
- Helium is also used to produce and sustain low temperatures required for super conductors, lasers, and super magnets. Super magnets are used in NMR spectrometers and magnetic resonance imaging (MRI) systems used in clinical diagnosis.