The noble gases are the nonmetal, inert elements in group 18 (previously known as group 0) of the perioic table. Chemically, they are very stable because they have the maximum number of valence electrons their outer shell can hold, causing them to rarely react with other elements. Under normal conditions, they are odorless, colorless, monatomic gases. The melting and boiling points for each noble gas are close together; consequently, only a small temperature range exists for each to be in a liquid state.