Assertion: $\mathrm{PF}_{5}, \mathrm{SF}_{6}$ and $\mathrm{H}_{2} \mathrm{SO}_{4}$ are the examples

Question

Assertion: $\mathrm{PF}_{5}, \mathrm{SF}_{6}$ and $\mathrm{H}_{2} \mathrm{SO}_{4}$ are the examples of expanded octet molecules.\ Reason : Octet rule is not applicable to the second period elements of the periodic table.

Professor PC Thomas Classes · Answer

(c):In $\mathrm{PF}_{5}, \mathrm{SF}_{6}$ and $\mathrm{H}_{2} \mathrm{SO}_{4}$, the central atom has more than eight valence electrons hence they exhibit expanded octet. This is possible due to availability of $3 d$ - orbitals.\ Elements in and beyond the third period of the periodic table do not follow octet rule thus it applies mainly to the second period elements of the periodic table.