Lewis Structures
Lewis structures show the arrangement of valence electrons in molecules. Master electron counting, octet rule, formal charges, resonance structures, and molecular geometry prediction.
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Study Tips
- ✓Count total valence electrons: group number for main group elements
- ✓The least electronegative atom is usually central (except H)
- ✓Minimize formal charges for the best Lewis structure
- ✓Check that total electrons match your count after drawing
Common Mistakes to Avoid
Students often miscount valence electrons, forget to show lone pairs, confuse molecular geometry with electron geometry, or draw resonance structures with atoms in different positions. Remember: resonance structures only move electrons, never atoms.
Lewis Structures FAQs
Common questions about lewis structures
Formal charge = Valence electrons - Non-bonding electrons - (1/2 x Bonding electrons). For the best Lewis structure, minimize formal charges and place negative formal charges on more electronegative atoms.
Atoms in period 3 and below can expand their octet because they have d orbitals available. Common examples include SF6, PCl5, and XeF4. Never expand octets for atoms in period 2 (C, N, O, F).
Electron geometry considers all electron domains (bonding and lone pairs) around the central atom. Molecular geometry describes only the positions of atoms. For example, water has tetrahedral electron geometry but bent molecular geometry.
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