Rabbit-ears hybrids, VSEPR sterics, and other orbital anachronisms

Abstract

We describe the logical flaws, experimental contradictions, and unfortunate educational repercussions of common student misconceptions regarding the shapes and properties of lone pairs, inspired by overemphasis on “valence shell electron pair repulsion” (VSEPR) rationalizations in current freshman-level chemistry textbooks. VSEPR-style representations of orbital shape and size are shown to be fundamentally inconsistent with numerous lines of experimental and theoretical evidence, including quantum mechanical “symmetry” principles that are sometimes invoked in their defense. VSEPR-style conceptions thereby detract from more accurate introductory-level teaching of orbital hybridization and bonding principles, while also requiring wasteful “unlearning” as the student progresses to higher levels. We include specific suggestions for how VSEPR-style rationalizations of molecular structure can be replaced with more accurate conceptions of hybridization and its relationship to electronegativity and molecular geometry, in accordance both with Bent's rule and the consistent features of modern wavefunctions as exhibited by natural bond orbital (NBO) analysis.