Short Answer

A coordinate covalent bond is a type of covalent bond in which both electrons in the shared pair come from the same atom. One atom donates a lone pair of electrons, while the other atom accepts it because it has an empty orbital. Once the bond is formed, it behaves just like a normal covalent bond.

This type of bond commonly forms in molecules such as ammonium ion (NH₄⁺), carbon monoxide (CO), and many complex ions. Coordinate covalent bonds help explain bonding in compounds where simple sharing of electrons is not enough to complete the outer shells of atoms.

Detailed Explanation :

Coordinate Covalent Bond

A coordinate covalent bond, also called a dative bond, is a special kind of covalent bond in which both electrons in the shared pair come from only one atom. In normal covalent bonds, each atom contributes one electron to the shared pair. However, in a coordinate covalent bond, one atom donates both electrons and the other atom accepts them. This bond is especially important in situations where an atom does not have electrons to share but has an empty orbital that can accept a lone pair.

Once the coordinate bond is formed, there is no difference in the behaviour of this bond compared to a regular covalent bond. The only difference lies in the origin of the electrons used to form the bond. This type of bonding helps explain many compounds and ions that cannot be fully understood by simple covalent bonding.

How a Coordinate Covalent Bond Forms

A coordinate covalent bond forms when:

• One atom has a lone pair of electrons (donor atom).
• Another atom has an empty orbital that can accept the lone pair (acceptor atom).

The donor atom provides both electrons to create a shared pair, and the acceptor atom provides the empty space. This allows both atoms to complete their valence shells and achieve stability.

Example: Formation of Ammonium Ion (NH₄⁺)

One of the best examples of this bond is the formation of the ammonium ion:

• Ammonia (NH₃) has a lone pair of electrons on the nitrogen atom.
• A hydrogen ion (H⁺) has no electrons, only a proton.
• Nitrogen donates its lone pair to the hydrogen ion, forming a coordinate covalent bond.

After the bond is created, the ammonium ion behaves as a stable ion with four N–H bonds, even though one of them was formed through coordination.

Example: Carbon Monoxide (CO)

Carbon monoxide is another classic example. In CO:

• Both carbon and oxygen share electrons, but oxygen donates one lone pair to carbon to complete its structure.
• This creates a coordinate covalent bond within the molecule.

This bond plays a major role in the structure and reactivity of carbon monoxide.

Example: Complex Ions and Coordination Compounds

Coordinate covalent bonds are extremely important in:

• Metal complexes
• Coordination compounds
• Ion formation

In many metal complexes, the metal ion has empty orbitals, and molecules like water, ammonia, or chloride donate lone pairs to form coordinate bonds. For example:

• In [Cu(NH₃)₄]²⁺, ammonia donates lone pairs to the copper ion.
• In [Fe(CN)₆]³⁻, cyanide ions donate lone pairs to iron.

This type of bonding explains the colour, magnetic behaviour, and structure of coordination compounds.

Characteristics of Coordinate Covalent Bonds

Some important features include:

1. Lone Pair Donation
   Only one atom provides electrons for the bond.
2. Presence of Donor and Acceptor Atoms
   The donor has a lone pair, and the acceptor has an empty orbital.
3. Once Formed, Behaves Like a Normal Covalent Bond
   Bond strength and length are similar to ordinary covalent bonds.
4. Often Found in Complex Ions
   Many metal ions use coordinate covalent bonds to form stable complexes.
5. Helps Complete Octets
   Useful when an atom cannot complete its octet by normal sharing.

Distinction Between Covalent and Coordinate Covalent Bond

Although both are covalent in nature, their formation is different:

• Covalent bond: each atom donates one electron.
• Coordinate covalent bond: one atom donates both electrons.

However, after formation, there is no difference in behaviour, strength, or bonding properties.

Importance in Chemistry

Coordinate covalent bonds are essential because:

• They help explain bonding in polyatomic ions (NH₄⁺, H₃O⁺).
• They play a key role in the field of coordination chemistry.
• They allow metals to bond with molecules through ligand donation.
• They help in the formation of stable biological structures, such as hemoglobin, where iron forms coordinate bonds.

These bonds are also used in industrial catalysts, where metal complexes speed up chemical reactions.

Conclusion

A coordinate covalent bond is formed when one atom donates both electrons to form a shared pair with another atom that has an empty orbital. Although different in formation from a regular covalent bond, the resulting bond behaves the same. Coordinate bonds are important in many molecules, ions, and metal complexes, helping atoms achieve stable structures where simple sharing of electrons is not possible.