Account for the following observations : Though fluorine is more electronegative than chlorine yet BF_3 is a weaker Lewis acid than Cl_3.

Account for the following observations : Though fluorine is more elec

1.	Account for the following observations : Though fluorine is more electronegative than chlorine yet BF_3 is a weaker Lewis acid than Cl_3.
Answer» Solution :In `BF_3`, boron has a VACANT 2P orbital and fluorine has one of the 2p orbital completely FILLED and unutilized. Both have same energy and can OVERLAP effectively to give `ppi-ppi` bond. While such type of bonding is not possible in `BCl_3` as there is no effective overlapping between the 2p-orbital of boron and 3p-orbital of chlorine. Therefore electron deficiency of B is higher than that of `BF_3`. Therefore `BF_3` is weaker Lewis ACID.