Question

In which of the following species bond length is
less than expected?
(1) NH3
(3) CC14
(4) BF3
(2) BF4-​

Answer 1

Answer:

In $BF_{3}$ the bond length is less than expected.

Explanation:

In case of $BF_{3}$ the octet of B is not completed as it has total six electrons (3 electrons of B itself and 3 electrons shared by F atoms) in its outer most shell. Also there is a vacant p orbital in B atom so the formation of pπ-pπ back bonding occurs between B and F atoms by the donation of electron from F to B. This back bonding generates a double bond character between B and F and results in the decrease in bond length.