Question
Explain coordinate bond by the orbital concept.
Solution
A coordinate bond is formed by the overlapping of an orbital of an atom containing a lone pair of electrons with the empty orbital of the other atom.
Let us consider the formation of ammonium ion (N+H4). It is formed by the combination of ammonia molecule and hydrogen ion.
The central nitrogen atom of ammonia molecule has one orbital containing a lone pair of electrons while the other three orbitals are filled up with bond pairs of electrons.
On the other hand, hydrogen ion has empty is orbital. When the H+ ion approaches ammonia molecule, its empty orbital overlaps the orbital of nitrogen atom containing a lone pair to form a dative bond. 
