Abstract: Traditional chemistry textbooks typically describe lone pairs as nonbonding electrons that do not participate in chemical bonding. However, emerging research demonstrates that lone pairs in ns² main-group cations can exhibit stereochemical activity through orbital coupling. This study employs a revised bonding model to elucidate the electronic origins of lone-pair activity, through examining representative systems including PbO/PbS, interstitial oxygen formation, and local distortions in halide perovskites. The work proposes educational strategies incorporating electronic-structure visualization and case-based learning to advance chemical bonding instruction toward an orbital-interaction–based understanding of structure–property relationships.

Key words: Lone-pair electron, Molecular orbital theory, Stereochemical activity, Revised bonding model, Case-based instruction