Lost in Lewis Structures:An Investigationof Student Difficulties in Developing Representational Competence

Many science, technology, engineering, and mathematics (STEM) students are required to take chemistry courses, even though the logic for this requirement is often opaque to them. A prime justification for such requirements is the assumption that chemistry is necessary for the development of a robust understanding of the relationship between molecular-level structure and the behavior of physical, chemical, and biological systems. The ability to predict the properties of a material from its molecular structure (and vice versa) is central to such an understanding. However, the links between molecular-level structure and properties are complex and require thoughtful study, practice, and skill. Without a robust understanding of these principles, students presented with the chemical structures of large biomolecules, for example, can only respond with surface-level learning and memorization. For many, the first step toward understanding structure-property relationships is the ability to draw and manipulate the simple chemical structures knownasLewis structures.These representations can convey a great deal of structural information and can be used to predict and explain a substance's physical and chemical properties. However, despite nearly four decades of literature describing “improved” ways of teaching Lewis structures (1-20), the creation of valid representations remains an elusive objective for many chemistry students, which leads us to the question: Why do students have such trouble with this task? After all, the rules for drawing Lewis structures are included in almost all chemistry texts, and indeed one author states (14, p 456) that “if students followa set of rules faithfully, the difficulties... [with student understanding] should not arise”. While the creation of Lewis structures is not an end in itself, it is a key component to understanding a wide range of chemical observations: flaws and ambiguities in students' ability to create correct structures will inevitably produce obstacles when they need to interpret and apply these structural representations. We believe that conventional approaches to introducing students to the skill of drawing a meaningful Lewis structure is in direct conflict with current understanding of how people actually learn, and likely to generate didaskalogenic (instruction-induced) confusions. What may appear to the expert to be a simple task is, in fact, inherently difficult, complex, counterintuitive, and all too often meaningless to many students.