Lewis structure theory holds that atoms within a molecule arrange their valence electrons so each atom attains a complete octet (or, for hydrogen, a filled duet), following a systematic procedure of counting valence electrons, assigning bonding and lone-pair electrons, and placing the least electronegative (lowest ionization energy) atom centrally. Formal charge, computed as valence electrons minus lone-pair electrons minus half the shared electrons, provides a quantitative criterion for selecting the most stable among candidate structures by minimizing charge separation and favoring negative charge on the more electronegative atom. Resonance describes cases where a single Lewis structure cannot adequately represent a molecule's electron distribution, requiring two or more structures with identical atomic arrangement but different electron placement to represent delocalized bonding, belonging to the domain of pre-quantum-mechanical molecular structure theory in general chemistry.
Lewis structure theory holds that atoms within a molecule arrange their valence electrons so each atom attains a complete octet (or, for hydrogen, a filled duet), following a systematic procedure of …