Back Bonding JEE Questions
Q1: The bond dissociation energy of B–F in BF3 is 646 kJ mol-1, whereas that of C–F in CF4 is 515 kJ mol–1. The correct reason for higher B–F bond dissociation energy as compared to that of C–F is
- Significant pπ–pπ interaction between B and F in BF3 whereas there is no possibility of such interaction between C and F in CF4.
- Lower degree of pπ–pπ interaction between B and F in BF3 than that between C and F in CF4
- Smaller size of B-atom as compared to that of C-atom
- Stronger bond between B and F in BF3 as compared to that between C and F in CF4.
Solution:
Because of pπ – pπ back bonding in BF3 molecule, all B-F bonds have partial double bond character.
Hence option (1) is the answer.
Q2: The formation of molecular complex BF3–NH3 results in a change in the hybridisation of boron
- From sp3 to sp3d
- From sp2 to dsp2
- From sp3 to sp2
- From sp2 to sp3
Solution:
In BF3, Boron atom has 3 bond pairs of electrons and 0 lone pairs of electrons. It is sp2 hybridized. In F3B-NH3, Boron atom has 4 bond pairs of electrons and 0 lone pairs of electrons. It is sp3 hybridized. So the formation of molecular complex results in a change in the hybridization of boron from sp2 to sp3.
Hence option (4) is the answer.
Back Bonding
Back Bonding occurs between atoms where electrons jump from the atomic orbital to the anti-bonding orbital of the acceptor ligand. Back Bonding is also known as π-Back Bonding or Back Donation. It is a type of covalent bonding where electrons from a filled atomic orbital jump to an empty or partially filled atomic orbital.
In this article, we will learn what back Bonding is, its definition, characteristics, and Back Bonding in BF3 and Metal Carbonyls.
Table of Content
- What is Back Bonding?
- Characteristics of Back bonding
- Pi Back bonding
- Back Bonding in BF3
- Back Bonding in Metal Carbonyls
- Back Bonding vs Coordinate Bonding