Dative bond or Co-ordinate covalent bond

Ø Lone pair: The pair of electrons which is not involved in any bond formation.

Co-ordinate covalent bond (or) Dative bond:

The bond formed by the sharing of electron pair between two atoms where one atom contributes both the electron.

Example 1  : Formation of Hydronium ion [H₃O⁺]:

  arrow between the atoms represents the co-ordinate covalent bond between Oxygen atom and Hydrogen where both the electrons coming from Oxygen atom but being shared by Oxygen and Hydrogen. This is due to the lone pair effect of Oxygen atom in water molecule.

Hydromium ion : 1-dative bond and 2 covalent bonds.

Example 2: Formation of Ammonium ion [NH₄⁺]:

Ammonium ion : 1- dative bond and 3- covalent bonds