Group 0 – Noble Gases
The group 0 elements are placed in the rightmost column of the periodic table. They are called the noble gases because they are all chemically unreactive (the term noble in chemistry signifies a lack of chemical reactivity). They are unreactive because their atoms have stable arrangements of electrons. All noble gases have the maximum number of electrons in their outer shell; i.e. 2 electrons for helium and 8 for the other five.
Noble gases are monoatomic, which means they exist as single atoms. This is because of their electronic stability. Unlike most common gases that exist as diatomic molecules like O2, N2, and Cl2, the noble gases exist as single atoms like He, Ne, Ar, i.e. they are monatomic molecules.