Noble gas

Noble gas, or inert gas, any of the elements in Group 0 of the Periodic Table, comprising helium, neon, argon, krypton, xenon, and radon. These are colorless, odorless gases whose outermost electrons are complete, making them chemically unreactive. Helium has 2 electrons in its outer shell; all the others have 8.

See also: Periodic table.