Abstract:

Introduction and Aims: Although understanding polarity provides students with insight into fundamental properties of molecules, research suggests that assigning polarity to molecules is often demanding. Work has shown that polarity can be made more meaningful for novices by exploiting different visualizations of charge distribution. This study aimed to investigate students’ assignment of chemical polarity using three modes representing electrostatic potential. The modes consisted of a colour gradient that maps the potential on the molecular surface, coloured lobes that indicates regions of negative (red) and positive (blue) potential, and a novel representation that uses green surface(s) to show the interface between regions of positive and negative potential. Given the importance of understanding and visualizing the concept of polarity in learning chemistry, this study raised the following research questions:

• Which of the modes will students use most successfully for accurately assigning polarity?
• Which of the modes will students use to assign polarity the fastest?

Methods: Students’ ability to assign polarity using the three visual modes was evaluated using a web-questionnaire. It contained 20 different molecules that were each displayed in the three modes together with a transposed ball-and-stick figure to indicate molecular geometry, yielding a total of 60 images. Molecules selected for inclusion consisted of 10 polar and 10 non-polar molecules which, in turn, comprised of 10 ‘simple’ and 10 ‘complex’ molecules. This ensured an equal representation with respect to both molecular polarity and structural complexity. Students were shown the images in a random sequence and required to assign polarity to each displayed molecule by clicking a “polar” or “non-polar” box. Nine first year student volunteers enrolled in an introductory chemistry course responded to the questionnaire. Responses were analyzed in the form of an accuracy score (correct/incorrect assignment of polarity) and time taken to assign polarity for each molecule.

Results: Students were able to successfully assign polarity to molecules using all the modes. Mean scores indicated that students used the red and blue lobes and the green surface representations most successfully for assigning polarity, while the electrostatic map mode was more difficult to use. Specifically, students were less successful in assigning polarity to polar molecules in comparison with non-polar molecules using the map mode. Interestingly, on average, students used the map mode to assign polarity the fastest. Thus, it seemed that students did not find assigning polarity using the map representation challenging, although it was least effective. A possible explanation for the lower scores for this mode is that the representational power of the map as a polarity assignment tool is compromised by the graphical detail of the colour gradient, especially when the molecule is both complex and polar. In this regard, the green surface representation was found to be a sensitive visual tool for assigning polarity to complex polar molecules.

Conclusions: The red and blue lobes and green surface modes are both powerful visualizations for assigning polarity. This was particularly evident in assigning polarity to simple polar molecules. Given the possible perceptual constraints associated with the map mode, the green surface mode offers a potentially valuable alternative for visualizing molecular polarity.

Keywords:

Visualization, Chemical polarity, Visual tools, Molecular representations, Web-based data collection, Teaching and learning, Chemical education.