Coordinate covalent bonds, also known as dative covalent bonds, are formed when one atom provides both electrons for the shared electron pair in the bond. Unlike typical covalent bonds where each atom contributes one electron, in a coordinate covalent bond, one atom "donates" its lone pair to another atom lacking electrons.
Here's a breakdown of the process:
-
Requirement: One atom must possess a lone pair of electrons (a pair of valence electrons not involved in bonding) and the other atom must have a vacant orbital or be electron-deficient.
-
Donation: The atom with the lone pair donates this pair to the atom with the vacant orbital.
-
Bond Formation: Once the lone pair is shared, a covalent bond is formed, just like a regular covalent bond. The only difference is the origin of the electrons.
-
Result: The atom that donates the electron pair gains a partial positive charge, while the atom that accepts the electron pair gains a partial negative charge.
Examples:
-
Formation of Ammonium Ion (NH4+): Ammonia (NH3) has a lone pair on the nitrogen atom. A proton (H+), which has no electrons, can accept this lone pair to form the ammonium ion.
NH3 + H+ → NH4+
In this case, nitrogen donates its lone pair to hydrogen, forming a coordinate covalent bond.
-
Formation of Hydronium Ion (H3O+): Similarly, a water molecule (H2O) can accept a proton (H+) to form the hydronium ion. The oxygen atom in water has two lone pairs, and it can donate one of these lone pairs to the proton.
H2O + H+ → H3O+
Key Differences from Covalent Bonds:
| Feature | Covalent Bond | Coordinate Covalent Bond |
|---|---|---|
| Electron Contribution | Each atom contributes one electron. | One atom contributes both electrons. |
| Formation | Sharing of electrons between two atoms. | Donation of a lone pair to an electron-deficient atom. |
| Electron Source | Both atoms provide electrons to the shared pair. | One atom provides both electrons for the shared pair. |
Once formed, a coordinate covalent bond is indistinguishable from a normal covalent bond. All bonds in a polyatomic ion like ammonium are equivalent.
