Question

Why $BC{I}_3$ is more acidic than $B{F}_3$ although the electro negativity is high for F than CI?

Answer 1

$BC{l}_3$ is more acidic than $B{F}_3$ because,in $B{F}_3$.

Boron in $S{P}^2$ hybridized with a vacant $2p$ orbital.

$F$ has one lone pair of electron which can overlap with vacant $2p$ orbital of boron which is called back bonding.

But in $BC{l}_3$,this effect is reduced as the size of $Cl$ is bigger in comparission to boron,so back bonding is less.

$BC{l}_3$ is more acidic than $B{F}_3$