Covalent and Coordinate Covalent Bonds
Covalent Bond
Definition:
A covalent bond forms when two atoms each contribute one electron to form an electron pair that the atoms share.
Characteristics:
Commonly forms between nonmetals.
Follows the octet rule
Forms stable molecular structures
Example: Hydrogen, H₂
Each hydrogen atom contributes one electron to form a shared pair:
H • • H → H–H
Coordinate Covalent Bond
Definition:
A coordinate covalent bond forms when one atom donates an entire electron pair and the other provides an empty orbital to accept it.
Characteristics:
Once formed, it is indistinguishable from an ordinary covalent bond
Common between molecules with lone pairs and cations.
Common in acid–base reactions and coordination compounds
Example: Ammonium Ion, NH₄⁺
The nitrogen atom in NH₃ has a lone pair that it can donate to H⁺ to form a coordinate covalent bond:
:NH₃ + H⁺ → NH₄⁺
NH₄⁺ has four N–H bonds, one of which forms through coordinate bonding
| Item | Covalent Bond | Coordinate Covalent Bond |
|---|---|---|
| Electron Source | Each atom contributes one electron | One atom contributes an electron pair |
| Formation Conditions | Atoms attract one another and share electrons | One atom has a lone pair; the other is electron deficient |
| Distinguishability | Distinguished by how the bond forms | Once formed, no fundamental difference from a covalent bond |
| Examples | H₂, O₂, CH₄ | NH₄⁺, H₃O⁺, [Cu(NH₃)₄]²⁺ |