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In two experiments, we examined how professional chemists (i.e., experts) and undergraduate chemistry students (i.e., novices) respond to a variety of chemistry representations (video segments, graphs, animations, and equations). In the first experiment, we provided subjects with a range of representations and asked them to group them together in any way that made sense to them. Both experts and novices created chemically meaningful groupings. Novices formed smaller groupings and more often used same-media representations. Experts used representations in multiple media to form larger groups. The reasons experts gave for their groupings were judged to be conceptual, while those of novices were judged to be based on surface features. In the second experiment, subjects were asked to transform a range of representations into specified alternative representations (e.g., given an equation and asked to draw a graph). Experts were better than novices in providing equivalent representations, particularly verbal descriptions for any given representation. We discuss the role that surface features of representations play in the understanding of chemistry, and we emphasize the importance of developing representational competence in chemistry students. We draw implications for the role that multiple representations-particularly linguistic ones-should play in chemistry curriculum, instruction, and assessment. © 1997 John Wiley & Sons, Inc. J Res Sci Teach 34: 949-968, 1997. The expansion of the universe, tectonic plate drift, evolution of the species, and molecular structure and reactivity are all scientific phenomena that are not available to direct experience. Whether the phenomenon is cosmological, geological, biological, or chemical, our window on the world is really very small. But perhaps more than other sciences, understanding chemistry relies on making sense of the invisible and untouchable. Much of what is chemistry exists at a molecular level and is not accessible to direct perception. Whereas the experiments used in classroom demonstrations are carefully selected to denote chemical processes by changing color, precipitating a solid, or giving off heat, most chemical reactions in the real world occur at rates that are so fast or slow, or their products are so dispersed, colorless, or odorless, as to make them difficult to detect.

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A prototype multimedia program, Multimedia and Mental Models in Chemistry (4M:CHEM), was developed to facilitate student learning in the classroom. 4M:CHEM utilizes a computer split-screen design to show simultaneous videos of real experiments, molecular-level animations of these experiments, real time graphs of macroscopic properties or structural diagrams, and chemical equations. These four windows can be shown individually or in any combination. When multiple windows are activated, actions in each are synchronized. These synchronized views of chemical phenomena may be paused and restarted in order to aid discussions of connections between and limitations of macroscopic, microscopic, and symbolic representations. The prototype program involves 32 experiments dealing with physical, gaseous, solution, and heterogeneous equilibria. Both qualitative and quantitative experiments are included to assist students in building chemical understanding and intuition as well as enhancing their quantitative problem solving abilities. An initial assessment of 4M:CHEM in two lecture sections for two one-hour presentations showed an increase in students' understanding of characteristics of systems at equilibrium and a marked decrease in misconceptions of chemical equilibrium.