<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The noble gases (historically also the inert gases) make up a group of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemical reactivity . The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). Oganesson (Og) is variously predicted to be a noble gas as well or to break the trend due to relativistic effects; its chemistry has not yet been investigated . </P> <P> For the first six periods of the periodic table, the noble gases are exactly the members of group 18 . Noble gases are typically highly unreactive except when under particular extreme conditions . The inertness of noble gases makes them very suitable in applications where reactions are not wanted . For example, argon is used in light bulbs to prevent the hot tungsten filament from oxidizing; also, helium is used in breathing gas by deep - sea divers to prevent oxygen, nitrogen and carbon dioxide (hypercapnia) toxicity . </P> <P> The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be "full", giving them little tendency to participate in chemical reactions, and it has been possible to prepare only a few hundred noble gas compounds . The melting and boiling points for a given noble gas are close together, differing by less than 10 ° C (18 ° F); that is, they are liquids over only a small temperature range . </P>

Where are noble gasses found on the periodic table