Helium (atomic symbol He) is the second most abundant element in the universe after hydrogen. Along with hydrogen and lithium, helium is believed to have been created in the first three minutes of the universe’s existence. It is one of the six noble gases, which are characterized by their great stability. The noble gases have full outer shells and do not readily react with other elements. Helium is atomic number 2, group 18 and period one of the periodic table. It was first discovered on the sun and is named for the Greek god of the sun, Helios.
The discovery of helium goes essentially hand in hand with the discovery of the nature of stars, and a great number of people were involved. For a long time, it was believed that without getting a star into a laboratory it would be impossible to determine what they were made of. In the mid-1800s giant strides were made in spectroscopy and the development of spectroscopes. The German scientists, Gustav Kirchoff and Robert Bunson, began burning materials and then studying the light they emitted, concluding that various colored spectral lines were a way to identify elements contained in the materials. This information was then extrapolated to the study of stars and their spectra to determine their composition.
In 1868 a total solar eclipse occurred, allowing the French astronomer, Pierre Janssen, to look at the sun and record its spectra. He noted a yellow line that Sir Norman Lockyer, an English astronomer, realized had a wavelength not matching that of any known elements. Lockyer named the new element helium, but not everyone in the scientific community accepted it until it was found on Earth. In 1895 the Scottish chemist, Sir William Ramsay, isolated helium from the radioactive mineral clevite while looking for argon. He did not find argon, but found something he thought may be Lockyer's helium. He sent a sample of the gas along to Lockyer and William Crookes. Lockyer and Crookes established that the unidentified and stable gas matched the one found in Janssen’s spectra of the sun.
Although helium is the second most abundant element in the universe, it only makes up 0.0005% of the earth’s atmosphere. Helium is so light that earth’s gravity is not strong enough to hold it and it escapes into space. The helium lost is replaced because helium is a by-product of radioactive decay, mainly uranium and thorium. It accumulates in natural gas pockets and seeps through cracks in the earth. For commercial use it is recovered from those gas pockets.
Helium is used mainly to cool superconducting magnets in MRI machines. Mixtures of helium and oxygen are used for divers and other people who work under pressure because it allows faster decompression than nitrogen. It is also used in instances that require inert barriers for safety, and of course to fill balloons and blimps because it is so light.
Helium is non-toxic, odorless and colorless. Helium has the lowest melting point of any element and its boiling point is near absolute zero. It is one of only two elements that have never been observed bonding to another element, along with neon. It takes extremely low temperatures or greater than normal pressure to get helium to change its state from a gas. Helium is the only element that does not solidify at absolute zero temperatures with normal pressure. Instead of solidifying or even liquifying, it becomes a superfluid, which has zero viscosity and will climb over walls of containers it is put in and leak from containers that appeared to be airtight.