|Atomic mass||4.00260 amu|
Helium was discovered in 1868 by a French astronomer by observation of the sun's spectrum. Its name is derived from the Greek helios, meaning the sun. It was thought at the time to be a metal, hence its name-ending -ium. It ought to be called helion in order to be consistent with the other noble gases.
Helium is a light, colourless gas with no smell or taste. It heads the list of elements commonly called the noble gases. Helium is inert, lighter than any other gas except hydrogen, and is useful for its lifting properties. It is the gas of choice for weather and birthday balloons since it is non-flammable.
Helium remains in the gaseous state until - 267.9°C, a few degrees above absolute zero. Helium's usefulness goes far beyond toy balloons and making you talk like Donald Duck. Because of the extremely cold temperature of liquid helium, Fermilab uses it along with liquid nitrogen to cool the giant superconducting magnets at the heart of the world's most powerful accelerator, the Tevatron. The magnets lose their superconductivity if the temperature rises past a few degrees above absolute zero.
Shown above is the glow discharge of helium.
Helium is chiefly the product of decay of radioactive elements and is found associated with ancient deposits of natural gas. It occurs as a minor constituent of natural gas in some oil fields in North America. It also occurs in the sun where it is formed by nuclear fusion of hydrogen. The earth's atmosphere contains about 5 parts per million of helium.
There is plenty of helium in the universe. It is possible to obtain helium gas directly from the atmosphere but the expense is prohibitive. Commercial volumes of helium gas are extracted from raw natural gas. Helium is separated from natural gas either by:
- adsorbing the other gases (i.e. mainly methane with some nitrogen gas) in materials like charcoal, or
- cooling the other gases until all but the helium are liquefied. As the temperature drops, the methane liquefies first, followed by the nitrogen. Helium remains a gas and it can be pumped off.