Helium (
He) is a colorless, odorless, tasteless, non-toxic,
inert monatomic chemical element that heads the
noble gas group in the
periodic table and whose
atomic number is 2. Its
boiling and
melting points are the lowest among the elements and it exists only as a
gas except in extreme conditions.
An unknown yellow
spectral line signature in light was first observed from a
solar eclipse in 1868 by French astronomer
Pierre Janssen who is jointly credited with the
discovery of the element with
Norman Lockyer who observed the same eclipse and was the first to propose this was a new element which he named helium. In 1903, large reserves of helium were found in the
natural gas fields of the
United States, which is by far the largest supplier of the gas. The substance is used in
cryogenics, in deep-sea breathing systems, to cool
superconducting magnets, in
helium dating, for inflating balloons, for providing lift in
airships and as a protective gas for many industrial uses (such as
arc welding and growing
silicon wafers). Inhaling a small volume of the gas temporarily changes the timbre and quality of the human voice. The behavior of liquid helium-4's two fluid phases, helium I and helium II, is important to researchers studying
quantum mechanics (in particular the phenomenon of
superfluidity) and to those looking at the effects that temperatures near
absolute zero have on
matter (such as
superconductivity).
Helium is the second lightest element and is the second most
abundant in the observable Universe. Most helium was formed during the
Big Bang, but new helium is being created as a result of the
nuclear fusion of hydrogen in
stars. On Earth, helium is relatively rare and is created by the natural
radioactive decay of some elements, as
alpha particles that are emitted consist of helium
nuclei. This radiogenic helium is trapped with
natural gas in concentrations up to seven percent by volume, from which it is extracted commercially by a low-temperature separation process called
fractional distillation.
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