Coordination Bonds: A Special Type of Covalent Bond
What is a Coordination Bond?
Definition
Coordination bond
A coordination bond (also known as a dative covalent bond) forms when both electrons in the shared pair come from the same atom.
This occurs when one atom, the donor, has a lone pair of electrons available, and another atom or ion, the acceptor, has an empty orbital ready to accommodate them.Example
- Consider a hydrogen ion ($H^+$), which is essentially a proton with no electrons.
- When it encounters a water molecule ($H_2O$), the oxygen atom in water can donate a lone pair of electrons to bond with the hydrogen ion, forming a hydronium ion ($H_3O^+$).
- The bond between the oxygen atom and the additional hydrogen ion is a coordination bond.
Key Characteristics:
- Once formed, a coordination bond behaves identically to a regular covalent bond.
- The donor atom is typically a Lewis base (an electron pair donor).
- The acceptor atom or ion acts as a Lewis acid (an electron pair acceptor).
Lewis acids and bases are discussed at HL level in Reactivity 3.4 topic.
Example- Consider the ammonium ion (NH₄⁺).
- It forms when ammonia (NH₃), which has a lone pair of electrons on its nitrogen atom, donates this pair to bond with a hydrogen ion (H⁺).
- This creates a coordination bond between nitrogen and the added hydrogen.
Real-World Examples of Coordination Bonds
1.Hydronium Ion ($H_3O^+$):
- When an acid dissolves in water, it releases $H^+$ ions.
- These ions immediately form coordination bonds with water molecules, resulting in hydronium ions ($H_3O^+$⁺).
This process is fundamental to understanding acidity in aqueous solutions.
2.Ammonium Ion ($NH_4^+$)
- The ammonium ion ($NH_4^+$) forms when ammonia ($NH_3$) acts as a base and accepts a proton ($H^+$).
- The nitrogen atom in ammonia has a lone pair of electrons, which forms a coordination bond with the proton, creating a positively charged ion.
This process is essential in acid-base chemistry and commonly appears in reactions involving ammonium salts, such as ammonium chloride ($NH_4Cl$).
3.Carbon Monoxide (CO)
- Carbon monoxide ($CO$) contains a coordination bond when it binds to metal centers in coordination complexes, such as in hemoglobin or metal catalysts.
