Helium is some really special stuff. All elements have properties which make them unique and in some cases extraordinary, but helium is an element with a whole list of exotic circumstances and notable effects. It is the second most abundant element in the universe, representative of 23 % of all matter, and yet, it is a rare Earth element. It is also the second lightest element. The vast majority of helium in the universe was created during the Big Bang, but it is also produced by fusion in stars, and here on Earth, in the form of alpha particles emitted by the radioactive decay of uranium, radium, and other radioactive elements.
Helium was first discovered, not here on Earth, but on the Sun. In 1868, Astronomer Pierre Janssen was performing a spectral analysis of the Sun during an eclipse. He noticed a previously unknown bright yellow line. It was the spectral signature of helium. It would take another 30 years, before anyone was able to isolate the element on Earth and begin to study its unique properties.
Helium can be extracted in small traces from some minerals, but most of it on earth is found in concentrations of natural gas, averaging 7% by volume. Helium is separated from natural gas through a process called fractional distillation. Essentially, the natural gas is cooled to cause the methane and other components of it to liquefy and be drawn off. When all of the gasses have been liquefied, the remaining gas is pretty much pure helium. Helium can be liquefied, but only at extremely low temperatures below 4.22K. All of the helium in the universe, so far as is known, exists in a gaseous state; only on earth with a little human tinkering can helium be cajoled into a liquid or quasi solid state. In its liquid form helium defies gravity, creeping up and over the rim of any container its poured into.
Helium is one of only a few elements that exhibits a rare phenomenon called superfluidity. In this quantum phase of matter, helium exhibits zero viscosity and therefore does not experience friction. If you had a volume of liquid helium in a container, and stirred it with a spoon to get it all moving in one direction, you could return years later to find it still churning in the same direction, that is however, if you could find some way to keep it from creeping out of the container.
Elemental helium atoms consist of 2 protons, 2 neutrons and 2 electrons. The stable configuration of its outermost shell of electrons gives the element an inert status explaining its monatomic structure, and the fact that it won’t react with itself or other elements to form compounds, except under extremely rare conditions. This fact also makes helium inflammable. Helium is the lightest of a group of elements called the “noble gases” which share helium’s stable electron configuration and inert properties. Helium has two isotopes helium-4, the common variety and helium-3 a very rare form of the element.
In a plasma state, helium, like neon, glows brightly emitting a light of iridescent quality. Helium plasma is highly conductive and effected by magnetic and electrical fields. These characteristics are exploited in helium argon lasers to focus photons into a narrow beam. Neon gas is used in neon signs because it is denser than helium. Helium could be but is not used in this manner, it would eventually defuse right through the glass escaping into the atmosphere; the light given off by the remaining gas diminishing.
One property of helium most folks have experimented with at one time or another, is to breath some of it in and notice a change in pitch and tone of voice, while exhaling the gas and talking. It brings a Mickey Mouse quality to your voice, a result of the fact that sound travels through helium three times faster than it does through air.
Helium has a lot of uses, it is added to air mixtures breathed by deep sea divers and astronauts to prevent nitrogen narcosis (the bends). In liquid form it is used in cryogenics and the manufacture of semiconductors. Being a lighter than air gas, helium is used to make dirigibles float, and off course, to fill balloons. Released into the atmosphere, helium floats to its uppermost reaches and eventually escapes the earths gravity, floating off into space in a process known as outgassing. For this reason, helium is becoming a rarer and thus more expensive commodity here on Earth. When the reserves of helium trapped in natural gas beneath the Earth’s surface, and inventories man has in storage have been depleted, there will be no more of the element found on earth in any substantial quantity. It would seem that here on Earth at least, helium is getting more special all the time.