Any of the elements in group 0 of the periodic table. In order of increasing atomic number, they are Helium, Neon, Argon, Krypton, Xenon, and Radon. Sometimes called the rare gases (although argon makes up 1% of the atmosphere), they are colorless, odorless and tasteless.

Inert gases have very low chemical activity because their outermost, or valence, electron is complete, containing two electrons in the case of helium and eight in the remaining cases.