2.2.1—Covalent bonding

A covalent bond is the electrostatic attraction between a shared electron pair and the nuclei of the bonded atoms. Lewis formulas show valence electrons and shared pairs.

Use the octet tendency to place shared and lone pairs, while remembering that the assessed Lewis scope allows up to four electron pairs around an atom.

Build a Lewis formula by counting all valence electrons, choosing a skeleton, completing outer octets and placing any remainder on the central atom. Then recount electrons and formal charge; a shared pair contributes to the attraction between both nuclei rather than belonging exclusively to either atom.

Charged-species check: NH₄⁺ has 5 + 4(1) − 1 = 8 valence electrons, so draw four N–H shared pairs, no lone pair on N, enclose the ion in brackets and write the overall + charge. A final audit must match the available electron total, complete the required outer-shell arrangements and reproduce the species charge; lone pairs, shared pairs and formal charges answer different parts of that audit.