why b-f bond length in bf3 (130 pm) and bf4 (143 pm) difer
Answers
Because of back bonding
❤.BF3 is a planar molecule in which B is sp2 hybridised.
❤.It has an empty 2P -orbital .
❤.F-Atom has three lone pairs of electrons in the 2p-orbitals.
❤. Because of its small size and strong inter electronic repulsions, pTT -pTT back bonding or back donation occurs in which a lone pair is transfered from F to B .
❤. As a result of this back bonding , B-F bond acquries some double bond characters .
❤. In contrast,in [BF-4] ion, B is sp3 hybridised and hence does not have an empty p-orbital available to accept the electrons donated by the F -atom.
❤. Consequently, in B-F is a purely single bond.
❤. Since double bonds are shorter than single bonds, the B-F bond length in BF3:is shorter (130pm) than B-F bond length (143pm) in [BF-4]
