Representing molecular behaviour

To those with little experience of the area, chemistry can be extremely daunting. Science has a reputation for being difficult to learn, and chemistry particularly so. Alex Johnstone offered an elegant explanation for this in his seminal paper on the subject.¹ He proposed that an expert in chemistry moves continuously between three distinct levels of thinking: the observable (macro) level, the molecular (sub-micro) level and the symbolic (representational) level.

At the observable level, the chemist sees, touches or senses in some other way the chemical change. At the molecular level, they use dynamic, imaginary mental images to explain observations in terms of structures and processes involving atoms, ions and – of course – molecules. Lastly, they describe, at the symbolic level, observed phenomena and molecularlevel structures and processes using chemical notation and mathematics. Considered this way, it is little wonder learners struggle.

The three thinking levels for the chemical reaction that occurs between silver nitrate solution and solid copper are shown in Figure 1. At the observable level, you can see dendritic silver crystals growing on the surface of the copper. At the molecular level, an animation can portray the dynamic, but imperceptible, formation of silver atoms as a growing crystal. Lastly, the equation summarises the reaction at the symbolic level.

Roy Tasker explains how molecular animations help students to achieve these three levels of thinking, potential issues around moldecular models, and the VisChem project, which aims to produce a suite of molecular animations which address student misconceptions identified in the literature.