He

He, with the chemical symbol He and atomic number 2, is a noble gas and the second lightest element. It is colorless, odorless, tasteless, and extremely inert, making it essentially nonreactive under normal conditions. The most common isotope is helium-4, with a rarer helium-3 isotope also occurring naturally. Helium is the second most abundant element in the observable universe by mass, formed mainly in the Big Bang and produced in stars.

Discovered in 1868 through spectroscopy of the Sun’s atmosphere by Jules Janssen and Norman Lockyer, it was named after Helios, the Greek god of the sun. On Earth, helium is scarce in the atmosphere (about 5 parts per million by volume) but accumulates in natural gas deposits, from which it is commercially extracted. Production involves processing natural gas and, in some cases, cryogenic separation of air to obtain helium.

Helium has an exceptionally low boiling point of 4.2 kelvin at one atmosphere, so it remains liquid at very low temperatures and is used as a coolant in cryogenics and in superconducting magnets, including MRI machines and research magnets. It also has applications in lifting balloons and airships, leak detection, and as an inert shielding gas in welding and various industrial processes. Although non-toxic and non-flammable, helium can cause asphyxiation if it displaces oxygen in enclosed spaces.

Because helium is a finite resource, its supply is closely managed, with attention to recycling and alternative cooling methods as demand remains high in industry and research.