JEE MainChemistryChemical Bonding and Molecular Structure
Two p-block elements A and B form trichlorides ACl ₃ and BCl ₃ . The molecule ACl ₃ has a dipole moment of zero, while BCl ₃ has a non-zero dipole moment. Which of the following statements correctly describes the Lewis acid/base character and the hybridization of the central atoms in ACl ₃ and BCl ₃ respectively?
Options
- AACl ₃ is a Lewis base ( sp ³ ) and BCl ₃ is a Lewis acid ( sp ² )
- BACl ₃ is a Lewis acid ( sp ² ) and BCl ₃ is a Lewis base ( sp ³ )
- CACl ₃ is a Lewis acid ( sp ³ ) and BCl ₃ is a Lewis base ( sp ² )
- DBoth ACl ₃ and BCl ₃ are Lewis acids with sp ² and sp ³ hybridizations respectively
Correct answer
B. ACl ₃ is a Lewis acid ( sp ² ) and BCl ₃ is a Lewis base ( sp ³ )
Step-by-step solution
A dipole moment of zero for ACl ₃ indicates a highly symmetrical geometry where the individual bond dipoles cancel out. For a molecule of type EX ₃ , this corresponds to a trigonal planar geometry. A trigonal planar geometry implies the central atom A has 3 bond pairs and 0 lone pairs (steric number = 3), which corresponds to sp ² hybridization. Since A has an incomplete octet (6 valence electrons), ACl ₃ can accept an electron pair, acting as a Lewis acid. A non-zero dipole moment for BCl ₃ indicates an asymmetric