Coordinate bonds are formed by the sharing of a pair of electrons, in which both electrons come from one atom or molecule. This is different from a covalent bond, in which each atom contributes one electron to the bond.

*The donor atom* is the atom or molecule that donates the pair of electrons. The donor atom typically has a lone pair of electrons.

*The acceptor atom* is the atom or molecule that accepts the pair of electrons. The acceptor atom typically has an empty orbital or a low-energy orbital that can accept electrons.

For the coordinate bond to form, the donor atom must have a lone pair of electrons, and the acceptor atom must have an empty orbital or a low-energy orbital that can accept electrons.

Example: Carbon monoxide reacts with water to form a carbon monoxide-water complex. In this complex, the oxygen atom of the water donates a pair of electrons to the carbon atom of the carbon monoxide.

$$H_2O + CO \rightarrow H_2O-CO$$