Formation of electron deficient compounds like BeCl3 , BF3 , AlCl3 . Central atom has less than 8e .
Formation of hypervalent compounds like PCl5, SF6, IF7, H2SO4 in which central atom has more than 8 electrons.
Formation of compounds of noble gases like XeF2, XeF4, XeF6 .
Odd electron molecules like NO, NO2.