BITSAT2019Chemistryp Block Elements (Group 13 & 14)Actual
The order of acidic strength of boron trihalides
Options
- ABF 3 < BCl 3 < BBr 3 < BI 3
- BBI 3 < BBr 3 < BCl 3 < BF 3
- CBCl 3 < BBr 3 < BI 3 < BF 3
- DBBr 3 < BCl 3 < BF 3 < BI 3
Correct answer
A. BF 3 < BCl 3 < BBr 3 < BI 3
Step-by-step solution
The strength of acidic character of boron trihalides depends upon pπ - pπ back bonding. In boron trihalides, pπ - pπ -back bonding occurs due to empty orbital of boron and filled orbitals of halogens. The pπ - pπ back bonding is shown maximum by BF 3 , as the size of B and F are small and comparatively same. Due to this effect tendency of accepting lone-pair of electrons of boron decreases as size of halogen increases. The order of size of halogens are F < Cl < Br < I . Thu