What is the Back Bonding?

(1) Back bonding is a type of weaker π bond which is formed by sideways overlapping of filled orbital with empty orbital present on adjacent bonded atoms in a molecule.
(2) It is also considered as intermolecular Lewis acid-base interaction as it is a π bond.
(3) Back bonding is found to be effective and considerable in following type of overlapping.

                [(i) 2p-2p, (ii) 2p-3p, (iii) 2p-3d]
(4) The extent of overlapping order is 
                     [2p-2p> 2p-3d >2p-3p]
(4) dx²-y² and dx² Orbital’s does not participate in back Bonding.

ILLUSTRATIVE EXAMPLE: Which of the following options is/are true about back Bonding?
(A) Sigma-dative bond

(B) π- dative bond

(C) Intermolecular Lewis acid-base interaction

(D) Intramolecular Lewis acid-base interaction
SOLUTION: Options B and D are responsible for back Bonding and options A and C are responsible for Coordinate Bonding.

Realated Questions:

Which is/are the correct statement/s about structure of methyl isothiocyanate (H3CNCS) and Silyl isothiocyanate(SiH3NCO)?

Why trimethyl amine {(CH3)3 N:} is pyramidal while trisilyl amine {(SiH3)3N:} is trigonal planer?