What are the rare gases?

Feb. 07, 2023

The rare gases, also known as the noble gases or the inert gases, are a group of six gaseous elements found in small amounts in the atmosphere: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Collectively they make up about one percent of Earth’s atmosphere. They were discovered by scientists near the end of the nineteenth century, and because they were so unreactive were initially called the inert gases. Although rare gases is used often to describe these elements, they are only rare in abundance relative to other gases found in the atmosphere of Earth.

Properties

The rare gases form group 18 of the periodic table of elements. This is the vertical column of elements on the extreme right of the periodic table. As with other groups of elements, the placement of all the rare gases in the same group reflects their similar properties. The rare gases are all colorless, odorless, and tasteless. They are also monatomic gases which means that they exist as individual atoms.

The most noticeable feature of the rare gases is their lack of chemical reactivity. Helium, neon, and argon do not combine with any other atoms to form compounds, and it has been only in the last few decades that compounds of the other rare gases have been prepared. In 1962, English-born American chemist Neil Bartlett (1932–), then at the University of British Columbia, succeeded in the historic preparation of the first compound of xenon. Since then, many xenon compounds containing mostly fluorine or oxygen atoms have also been prepared. Krypton and radon have also been combined with fluorine to form simple compounds. Because some rare gas compounds have powerful oxidizing properties (they can remove electrons from other substances) they have been used to synthesize other compounds.

The low reactivity of the rare gases is due to the arrangement of electrons in the rare gas atoms. The configuration of electrons in these elements makes them very stable and therefore unreactive. The reactivity of any element is due, in part, to how easily it gains or loses electrons, which is necessary for an atom to react with other atoms. The rare gases do not readily do either. Prior to Bartlett’s preparation of the first xenon compound, the rare gases were widely referred to as the inert gases. Because the rare gases are so unreactive, they are harmless to living organisms. Radon, however, is hazardous because it is radioactive.

Uses

The properties of each rare gas dictate its specific commercial applications. Because they are the most abundant, and therefore the least expensive to produce, helium and argon find the most commercial applications. Helium’s low density and inertness make it ideal for use in lighter-than-air craft, such as balloons and blimps. Although helium has nearly twice the density of hydrogen, it has about 98% of hydrogen’s lifting power. A little over 324.7 gal (1,230 l) of helium lifts 2.2 lb (1 kg). Helium is also nonflammable and therefore considerably safer than hydrogen, which was once widely used in gas-filled aircraft. Liquid helium has the lowest boiling point of any known substance (about -452°F; -269°C) and therefore has many low-temperature applications in research and industry. Divers breathe an artificial oxygen-helium mixture to prevent gas bubbles forming in the blood as they swim to the surface from great depths. Other uses for helium have been in supersonic wind tunnels, as a protective gas in growing silicon and germanium crystals and, together with neon, to make gas lasers.