3.4.1—Covalent bonding examples

A covalent bond is the electrostatic attraction between the positive nuclei of two atoms and a shared pair of outer-shell electrons. The atoms share rather than transfer electrons, allowing the specified non-metal atoms to reach a more stable outer-electron arrangement.

One shared pair gives a single covalent bond; two shared pairs give a double bond; three shared pairs give a triple bond. Use the outer-shell electrons to account for the shared pairs in the specified molecules, including H₂, O₂, N₂, Cl₂, HCl, CO₂, NH₃, CH₄, C₂H₆ and C₂H₄.

In a dot-and-cross representation, show only the relevant outer-shell electrons, use dots and crosses to distinguish the two atoms, and place shared electrons as pairs between the nuclei. Keep lone pairs and shared pairs visible when they are needed to justify the structure.

For the supported Period 3 cases SO₂, PCl₅ and SF₆, the central atom may have an expanded octet. A coordinate bond is still a shared pair, but both electrons originate from one donor atom: use NH₃ + H⁺ → NH₄⁺ and Al₂Cl₆ only at this source-supported level. Orbital overlap, hybridisation, bond energy and bond length belong to neighbouring objectives.