NTA Abhyas JEE Main2020Chemistryp Block Elements (Group 13 & 14)Practice
Which of the following statements is correct?
Options
- AB C l 3 and A l C l 3 are both Lewis acids and B C l 3 is stronger than A l C l 3
- BBoth B C l 3 and A l C l 3 are Lewis acids and A l C l 3 is stronger than B C l 3
- CBoth B C l 3 and A l C l 3 are equally strong Lewis acids
- DBoth B C l 3 and A l C l 3 are not Lewis acids
Correct answer
A. B C l 3 and A l C l 3 are both Lewis acids and B C l 3 is stronger than A l C l 3
Step-by-step solution
In B C l 3 , p π - p π back-donation occurs between the vacant 2p-orbital of 'B' and fully-filled 3p-orbital of Cl of a B - C l bond. This p π - p π overlapping is not much effective, because of dissimilar sizes of 2p and 3p-orbitals. But in A l C l 3 , p π - p π overlapping is more effective, because p-orbitals of Al and Cl belongs to the same energy levels and hence, they are of similar sizes. As a result of back-donation, the electron-deficiency of Al atom gets more compensated as compared with 'B' in B C l 3 an