covalent bond
A covalent bond is a chemical bond formed when two atoms share one or more pairs of electrons so that each can achieve a more stable electron configuration, often a full outer shell. This shared pair of electrons is attracted by the nuclei of both atoms, creating a stable link between them.
What is a covalent bond?
- A covalent bond is an interatomic link created by sharing an electron pair between atoms rather than transferring electrons as in ionic bonding.
- It typically occurs between non‑metal atoms with a small electronegativity difference (usually less than about 2), so neither atom fully takes the electrons away from the other.
- The sharing of electrons helps atoms reach a more stable valence configuration, often satisfying the octet rule (or duet for hydrogen).
Types of covalent bonds
- Single bond : One shared pair of electrons (2 electrons), as in H₂ and CH₄.
- Double bond : Two shared pairs (4 electrons), as in O₂ and CO₂.
- Triple bond : Three shared pairs (6 electrons), as in N₂ and C₂H₂.
By polarity
- Nonpolar covalent bond : Electrons are shared equally because the atoms have the same or nearly the same electronegativity, as in H₂, O₂, and N₂.
- Polar covalent bond : Electrons are shared unequally when electronegativity differences are between about 0.1 and 2, creating partial positive and negative charges, as in H₂O and HCl.
Coordinate (dative) covalent bond
- In a coordinate covalent bond, both shared electrons come from the same atom, but once formed it behaves like an ordinary covalent bond.
- Common examples include bonds in NH₄⁺, H₃O⁺, and some metal–ligand complexes like BF₃·NH₃.
Quick real‑world examples
- Water (H₂O): Oxygen forms two polar covalent bonds with hydrogen, giving the molecule partial charges and many of its unique properties.
- Methane (CH₄): Carbon forms four single covalent bonds with hydrogen, creating a stable tetrahedral molecule.
- Nitrogen gas (N₂): Two nitrogen atoms are joined by a strong triple covalent bond, making N₂ very stable and relatively unreactive under normal conditions.
How to picture a covalent bond
- In a Lewis structure, a covalent bond is shown as a line between atoms, representing a shared electron pair (for example, H–H or O=O).
- Diatomic molecules like H₂, O₂, and N₂ are classic examples where two identical atoms share electrons, often forming pure nonpolar covalent bonds.
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