The six (seven when you include Ununoctium as one, but not everyone agrees or it doesn't seem to work that way) noble gases are labeled as group 18 of the periodic table. These elements were considered to be not-chemically reactive gases until the 1960's. That is because of their oxidation number of 0 prevents the noble gases from forming compounds readily. All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium 8 for all others) making them stable.
HELIUM
NEON
ARGON
KRYPTON
RADON
By Onaizah Fabrigas