In which of the following molecules octet rule is not obeyed and why?

(A) BF3
(B) SF4
(C) NF3
(D) H2O2?

Question

In which of the following molecules octet rule is not obeyed and why? (A) BF3 (B) SF4 (C) NF3 (D) H2O2?

Answer

In BF3,octet rule is not followed as boron forms only three bonds(6 electrons)....B is a 2nd period element and hence has a maximum covalency of 3....  also due to absence of vacant d-orbitals it is unable to expand it's octet.... hence it is electron deficient in nature....thus it behaves as a Lewis acid(electron acceptor)....

Answer

Boron commonly makes only three covalent bonds, resulting in only six valence electrons around the B atom. A well-known example is BF 3: The third violation to the octet rule is found in those compounds with more than eight electrons assigned to their valence shell.

Answer

In BF3, the octet rule is not followed as it has only 6 electrons in its Lewis structure. This is because boron has 3 electrons only for sharing and it cannot extend its covalency beyond 3 due to absence of d orbital. The compound is thus called electron deficient compound. So, option a is correct.

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