Dot-and-cross becomes Lewis + VSEPR + formal charge + resonance + hybridisation

Draw dot-and-cross diagrams for simple molecules. Shape is not required. Double bonds appear in O₂ and CO₂.

A ladder of tools.

• Lewis formulas including lone pairs, with a systematic electron-count method.
• VSEPR (2.2.4): count electron domains around a central atom, get the electron-domain geometry, then the molecular shape after ignoring lone pairs; lone pairs repel more strongly, compressing bond angles (~2.5° per lone pair for the common cases). Bond angles must be quoted.
• Coordination (dative) bonds (2.2.3), where both electrons come from one atom.
• Resonance (2.2.11–2.2.12): benzene, carbonate, nitrate; the real structure is a single delocalised species, not an oscillation between forms.
• Expanded octets (2.2.13) and formal charge (2.2.14) as a tie-breaker between candidate Lewis structures. (HL)
• σ and π bonds (2.2.15) and hybridisation sp/sp²/sp³ (2.2.16). (HL)

Structure drawing becomes a predictive activity — from a formula you must derive geometry, polarity, and bonding character. This is heavily examined and is fully algorithmic once learned, which makes it high-value early practice.

VSEPR needs the idea of electron-pair repulsion in 3D; GCSE assessment is 2D.

Forgetting lone pairs when counting domains (giving CH₄, NH₃ and H₂O all as 109.5°); confusing electron-domain geometry with molecular shape; thinking resonance means the molecule flickers; assuming a molecule with polar bonds must be polar (CO₂, CCl₄ are the counterexamples).