Addressing the Hypervalent Model: A Straightforward Explanation of Traditionally Hypervalent Molecules

Abstract

The concept of an atom with an expanded octet, known as hypervalency, has persisted in the general chemistry curriculum, despite abundant theoretical work disputing its veracity. Here, the electronic structure of traditionally hypervalent molecules (H2SO3, H2SO4, PF5, and SF6) is explored through quantum chemical calculations to illustrate the inaccuracies of hypervalency. Through the framing of ionic and dative bonding, an alternative way to conceptualize bonding in such molecules is introduced based on the octet rule already canonized in the general chemistry curriculum. These results are used to construct new Lewis structures that more accurately describe their chemical nature while simultaneously reducing the complexity of drawing Lewis structures. Teaching applications and heuristics are discussed with the hope that these models may eventually supplant hypervalency in the curriculum.