The bond dissociation energy of B-F in BF_(3) is 646 kJ "mol"^(-1) whereas that of C-F in CF_(4)is 515 kJ "mol"^(-1).The correct reasonfor higherB-Fbond dissociationenergy as compared to thatof C-F is

The bond dissociation energy of B-F in BF_(3) is 646 kJ "mol"^(-1) whe

1.	The bond dissociation energy of B-F in BF_(3) is 646 kJ "mol"^(-1) whereas that of C-F in CF_(4)is 515 kJ "mol"^(-1).The correct reasonfor higherB-Fbond dissociationenergy as compared to thatof C-F is
Answer» stronger `sigma`-bond between B and F in `BF_(3)` as compared to that between `C` and `F` in `CF_(4)` significant `ppi-ppi`interactionbetween B and F in `BF_(3)` whereas there is no POSSIBILITY of suchinteraction between C and F in `CF_(4)` LOWER degree of `ppi-ppi`interactionbetween B and F in `BF_(3)` than that between C and F in `CF_(4)`. smaller size of B-atom as compared to that of C-atom Solution :Due to identical size of 2p-orbitalson B and F,back donation of a LONE PAIR of electrons from the filled 2o-orbitals of F to the empty 2p-orbital of B occurs to a considerable extent. As a result , `B-F`bond has some double character and hencebond dissociationenergy of `B-F`bond in `BF_(3)`is much higherthan that of C-F bondin `CF_(4)`.the reasonbeingthat C does not have an empty 2p-orbitals and hence back donation does notoccur.