The value of modelling molecules

It is well known that a solid grasp of visual-spatial representations is essential for success in studying chemistry. One aspect of organic chemistry that makes it particularly challenging for students is the wide range of representations encountered during teaching. These include formulae (molecular, structural, displayed and skeletal), dash-wedge diagrams, along with Fisher and Newman projections.

While instructors may urge students to use molecular models to visualise spatial structures based on 2D representations, evidence shows they rarely do. Two recent articles, one by Andrew Stull and colleagues,¹ and the other by Boukhechem Mohamed-Salah and Dumon Alain,² explore the impact of model use on the ability of students to interpret and manipulate different types of representation.

Dealing with spatial representations is challenging because of the demand placed on our limited spatial working memory. Translating between different diagrams involves the difficult task of transforming representations, which often involves imagining a process of rotation. Manipulation of a model to visualise the process allows students to offload cognition onto an external object, so reducing the demand on their working memory.

Both articles present compelling evidence regarding the value of models in supporting student learning, through the demonstration of improved translation between multiple 2D formats. However, Dumon’s study suggests Fisher projections are still problematic due to the lack of coverage in teaching.

Andrew’s work emphasises the importance of actively demonstrating to students how they should use models while solving problems through the provision of teaching activities that encourage such an approach. The implication is that students will only use models proactively once they understand their value.  Furthermore, the study supports the suggestion that students who lack spatial reasoning capabilities can improve their skills in this area through their work with models.

Dumon emphasises the importance of explicitly discussing different types of diagram during teaching, and suggests students should have opportunities to draw and describe 2D diagrams with reference to ball and stick models. Finally, both articles stress the value of using models to deliver feedback to students in a way that allows them to confront illusions of understanding or overconfidence in performance, providing an opportunity to develop rich internal models that can be applied to the manipulation of representations in the future.