Noble gases are those that are chemically inert, and do not react with any other elements under normal circumstances. Their outer shell has a full complement of electrons.
The gases are
Argon, Krypton, Neon, Xenon, Radon, and Helium
Their lack of reactivity is useful in some applications (Incandescent light bulbs are filled with argon, for instance). Argon makes up about 1% of the earth's atmosphere.
