The elements which belongs to the period 1 and 2 have two orbitals and the maximum number of electrons they can retain in their outermost shell is 8 therefore, they follow octet rule. The group of element which cannot expand their valency to the d orbital do not follow octet rule. This rule is followed by the elements like carbon, nitrogen, oxygen and halogens. Some of the metals do not follow this rule except sodium, magnesium etc. Moreover, hypervalent molecules, transition metals, free radicals and trivalent bonds also do not follow octet rule.
