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The B-F bond length in BF3 is shorter th...

The B-F bond length in `BF_3` is shorter than that in `BF_4^(-)`. This is because of

A

resonance in `BF_3` but not in `BF_4^(-)`

B

`p pi-p pi` back bonding in `BF_4^(-)` but not in `BF_3`

C

`p pi-p pi` back bonding in `BF_3` but not in `BF_4^(-)`

D

`p pi-d pi` back bonding in `BF_3` but not is `BF_4^(-)`

Text Solution

Verified by Experts

The correct Answer is:
C
In `BF_3`, boron is `sp^3` hybridised. It has a vacant 2p-orbital. Each fluorine in `BF_3` has completely filled unutilized 2p-orbitals. Since, both of these orbitals belong to same energy level, `p pi-p pi` back bonding occurs in which a lone pair of electron-is transferred from unutilized, completely filled 2p-orbital of Fto vacant 2p-orbital of B. This type of bond formation is known as back bonding. Therefore, B-F bond has some double bond character. That.s why all the three boron-fluorine bonds are shorter than the usual single boron-fluorine bond.
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