Why Are Group 18 Noble Gases Inert?

Noble gases are inert due to their complete electron shells. Their stable atomic structure makes the energy required to add or remove an electron prohibitively high, so the noble gases do not form compounds in natural conditions.

Although they are inert in nature, noble gases can form compounds in certain laboratory conditions. They must either be ionized or subjected to high pressure, and even under these conditions only bond with highly reactive elements. Halogens are the elements most likely to bond with noble gases in the laboratory; the resulting compounds are used as oxidizers in other chemical reactions. They are particularly useful in reactions where contamination from the oxidizing compound is not desirable, since the noble gas is released as part of the oxidizing reaction.

The noble gases form group 18 of the periodic table and are helium, neon, argon, krypton, xenon and radon. Although it is a member of group 18, the synthetic, radioactive element ununoctium is not classified as a noble gas. Ununoctium is highly unstable and only a few atoms have been produced in laboratories, but theoretical calculations predict that it is a solid rather than a noble gas. The only other radioactive element in group 18 is radon.