Helium is a so-called “noble” gas, meaning that under almost any conditions, it does not chemically react with other elements. It contains a full outer valence shell of electrons, making each atom very reluctant to either donate or share valence electrons with surrounding elements to form bonds. Helium is therefore inherently unreactive, at least under anything but the most strenuous of reaction conditions. This very characteristic, which at first would seem to hamper its use, is key to its commercial applications. Lighter than air (density = 0.178 g/ml), colorless, odorless, and nontoxic, helium is valued for its many unique applications. It can be put to work way above ground, above ground, on the Earths surface, and below the surface. It is certainly ubiquitous and this curious and versatile element finds uses all around use.
Various space programs find use for helium when it comes to pressurizing liquid fuel rockets. As mentioned elsewhere on this site, liquid fuels are temperamental beasts, often filled with corrosive substances that would quickly react with the interior surfaces of the metal rocket casing. By filling and pressuring the interior with inert helium, this problem is avoided. As a companion in the skys, helium gas is used to fill everything from carnival balloons to full scale blimps (zeppilins, named after Court Ferdinand von Zepplin, a German general who perfected the design). Unlike hydrogen, helium is not flammable, and since it is lighter than air the zeppilin rises.
More down to earth, helium can be used as a cooling medium for nuclear reactors, as it does not absorb the neutron flux in most typical nuclear flux. It can also be used as an inert gas “blanket” when arc welding reactive metals such as titanium, which would normally react with the oxygen in the air. Divers find use for helium underwater by mixing their breathing tanks to a mixture of 80% helium and 20% oxygen.
Liquid helium (bp = -452 degrees Fahrenheit ) can save more than divers lives; it is commonly used to cool superconducting magnets, such in the MRIs found in hospitals as well as the magnets found in the Large Hadron Collider in CERN, Switzerland.
Helium is in fact so valuable that the United States Government decided in 1925 to establish a “National Helium Reserve” near Amarillo, Texas – an underground dome filled with an astonishing billion cubic meters of the gas. It is truly a remarkable substance.