Coordination (Dative) Bond
A coordination bond (historically called a coordinate bond or dative bond) is a covalent bond in which both electrons in the shared pair are provided by one atom (the donor). The other atom (acceptor) has an empty orbital.
Once formed, a coordination bond is identical in strength and length to an ordinary covalent bond. It is represented by an arrow (→) pointing from the donor to the acceptor.
Key Examples
Ammonium (NH4⁺)
NH₃ has a lone pair on nitrogen. When H⁺ (empty 1s orbital) approaches, nitrogen donates both electrons to form the 4th N-H bond. All four bonds become equivalent.
Carbon Monoxide (CO)
Carbon and oxygen share a triple bond. Two of the three bonds are conventional; the third is a coordination bond where oxygen donates a lone pair to carbon's empty orbital.
Hydronium (H3O⁺)
Water has two lone pairs on oxygen. When H⁺ bonds to water, oxygen donates one lone pair to form a coordination bond → H₃O⁺. This is how acids protonate water.
Ammonium (NH4⁺)
In Lewis diagrams, all four N-H bonds in NH₄⁺ are indistinguishable. The coordination bond is only different in how it was formed, not in its final properties. Don't mark one bond as "special" unless specifically asked about formation.
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