Back bonding is also called as “ π_co_ordinate bond ”

Compounds are of two types that show back bonding they are:-

1)compounds in which side atoms donating e-pair to central atom ex: BF3(boron triflouride).

2)compounds in which central atom donating the electron pair to side sources ex:N(SiH3)3.

Conditions for back bonding are:_

1)any one atom in the pair should contain atleast one lone pair.

2) atleast one atom belongs to 2nd period and other belongs to 3rd period.

Observe it once here central atom is electron deficient and side atom is rich ,both belongs to 2nd period ..

Note:_

Strength of back bonding is directly proportional to size of atom i.e

2p-2p > 2p-3p > 2p-3d

In terms of orbitals size

Here 2p-2p example is: BF3

2p-3p example is : BCl3

2p-3d example is : PF3