The monatomic molecule here is
Diatomic molecules are
Polyatomic molecules are
Noble gases like
Elements that do need an extra electron to complete their outer shells include
If there are no other types of atoms present to react with, the atoms will react with each other to share an electron to complete their shells and become more stable as a diatomic molecule.
Polyatomic molecules occur as the result of special reactions and are often allotropes of a substance.