Co-ordinate covalent bond

Coordinate covalent bond (dative bond) is a special type of covalent bond. It is proposed by Sidgwick. It is formed by the sharing of electrons between two atoms in which both the electrons of the shared electron pair are contributed by one atom and the other atom nearly participates in sharing.

The bond is represented as (“\longrightarrow“) an arrow starting from the donor atom and directed towards the acceptor atom.

Examples : Ammonia – Boron trifluoride   \text {H}_{3} \text {N} : \longrightarrow \text {BF}_{3}

Ammonia combines with boron trifluoride to give ammonium boron trifluoride.

coordinate covalent bond Ammonia - boron trifluoride
In ammonia nitrogen has a complete octet and also it has a lone pair of electrons. In \text {BF}_{3} the boron atom has a total of six electrons after sharing with fluorine. Nitrogen donates the electron pair to boron to form a co – ordinate covalent bond between ammonia and boron trifluoride.

2) Ammonium ion \text {(NH}_{4}^{+})

Ammonium ion
Hydronium ion \text {(H}_{3} \text {O}^{+})

Hydronium ion

Properties of coordinate covalent bond :

The bond does not ionize in water.

The compounds are generally soluble in organic solvents and are sparingly soluble in water.

These compounds exhibit space isomerism because the bond is rigid and directional.

The bond is semipolar in nature – so their volatility lies in between covalent and ionic bonds.