Coordinate  covalent bond

A coordinate or a dative bond is established between two such atoms, one of which has a complete octet and possesses a pair of valency electrons while the other is short of a pair of electrons.

Note:  Coordinate bond after formation is indistinguishable from a covalent bond.

The formation of a coordinate bond can be looked upon as a combination of electrovalent and covalent bonds. The formation may be assumed to have taken place in two steps:

(a) The donor atom loses one electron and transferred to acceptor atom. As a result donor atom acquires a positive charge and the acceptor atom acquires a negative charge.

(b) These two charged particles now contribute one electron each and this pair is shared by both the atoms.

As the coordinate bond is a combination of one electrovalent bond and one covalent bond, it is also termed as semi polar bond.The compound consisting of the coordinate bond is termed coordinate compound.

Characteristics of Coordinate Compounds :

 The main properties are described below:

1. These compounds exist as gases, liquids and solids under ordinary conditions.

2. Melting and boiling points are higher than purely covalent compounds and lower than purely ionic compounds.

3. These are sparingly soluble in polar solvents like water but readily soluble in non-polar (organic) solvents.

4. These are as stable as the covalent compounds. The addition compounds are, however, not very stable.

5. Like covalent compounds, these are also bad conductors of electricity.

6. Molecular reactions: These undergo molecular reactions. The reactions are slow.

7. Isomerism: The bond is rigid and directional. Thus, coordinate compounds how isomerism.

8. Dielectric constant: The compounds containing coordinate bond possess high values of dielectric constants.