Date of Award
Spring 2025
Project Type
Dissertation
Program or Major
Chemistry
Degree Name
Doctor of Philosophy
First Advisor
Christopher Bauer
Second Advisor
Carmela Amato-Wierda
Third Advisor
Anyin Li
Abstract
Molecular polarity is a key foundational concept for understanding structure-property relationships in chemistry. Classifying molecular polarity is challenging for novice students because it is abstract and depends simultaneously on the polarity of the covalent bonds and the three-dimensional (3D) symmetry of the molecule. Perceptual learning modules are designed to accelerate the development of pattern recognition and fluency through making many classifications based on varied structures and receiving immediate feedback; they are expected to produce long-lasting gains in generalization and fluency.
The first exploratory study compared three different treatment conditions of General Chemistry 1 students participating in a perceptual learning module that involved characterizing molecular polarity based on the perception of three-dimensional (3D) symmetry in molecular representations. The treatment groups differed based on the mode of presentation of exemplar molecules and the type of molecular representations, but they were controlled for time-on-task and number of exemplars. One treatment group only received feedback on ball-and-stick molecules presented sequentially, while the other two groups also viewed a simultaneous array of generic ball-and-stick polar and nonpolar exemplar molecules, with or without electrostatic potential map (EPM) overlays. All participants completed a final transfer block that tested their ability to generalize what they had learned to new molecules. A similar qualitative study recorded and transcribed the dialogue of nine pairs of students across the three treatment conditions completing similar online modules. The results showed that students across all treatment groups and time-cohorts were able to use the perceived 3D symmetry of molecules to classify molecular polarity based on ball-and-stick representations with roughly 90% accuracy for comparable new molecules after viewing 50+ exemplars total. Furthermore, participants across all treatment groups showed 73–84% accuracy in generalizing to larger more novel molecules. Most quantitative results showed no differences between the three treatment groups. However, the results of the qualitative analysis suggested that the simultaneous arrays helped to prompt greater sensemaking compared to the sequential condition, and the EPMs may have been overwhelming for students with low prior knowledge. Furthermore, the study transfer block data broken out by student achievement quartile revealed that students in the lowest achievement quartile struggled to characterize molecules with partial symmetry (i.e., those having a vertical symmetry plane, but no horizontal symmetry plane) (e.g., sulfur dioxide, cis-1,2-dichloroethylene) and they showed similar uncertainty for the trigonal pyramidal phosphorus trichloride. The results of long-term data at the end of General Chemistry 2 revealed students were still barely better than chance at characterizing molecular polarity from molecular formulas, with students showing roughly 60% accuracy across all the molecules tested; there was no evidence of long-term learning gains for study participants.
The follow-up intervention study used a Pre/Post design for a similar online learning module aimed at improving students' perceptual learning and conceptual understanding of molecular polarity. In the module, students reviewed molecular polarity concepts during guided inquiry / tutorial sections and then practiced assigning polarity over four sets of 10 molecules each. The intervention study contained a greater variety of exemplar molecules and provided higher quality feedback pages for each compared to the exploratory study. The quantitative results from the Pre/Post assessment indicated the molecular polarity intervention was generally quite effective in producing large student learning gains in correctly characterizing molecular polarity, demonstrating basic understanding of the connections between symmetry, bond polarity, and molecular polarity, and recognizing that both symmetry and bond polarity factors contribute simultaneously to molecular polarity. Furthermore, the Pre/Post results broken out by student achievement quartile suggested students in the higher achievement quartiles showed the largest gains for most measures, but students in the lower achievement quartiles showed the largest gains in demonstrating basic understanding of the connections between symmetry, bond polarity, and molecular polarity. The intervention also aimed to provide a scaffold for helping students learn to characterize polarity based on molecular formulas by transitioning gradually from only 3D ball-and-stick representations, to also including two-dimensional (2D) Lewis structures, and eventually molecular formulas by the end. Results from the practice molecules of different representations revealed most students were successful in accurately characterizing polarity for most 3D and 2D representations of molecules, but students were much less successful based on molecular formulas. The other most challenging aspects of the intervention included molecules that had partial symmetry (i.e., those having a vertical symmetry plane, but no horizontal symmetry plane) (e.g., dimethyl ether, Z-diazene) and molecules that were falsely represented as linear Lewis structures. Compared to the exploratory study, students in the intervention study experienced more widespread difficulty with molecules that had partial symmetry. The long-term effectiveness of the molecular polarity intervention was approximated by comparing the results of the total population of student respondents at the end of General Chemistry 2 following the intervention study with those following the exploratory study. Results showed there were more molecules showing larger and improved outcomes than worse outcomes, suggesting that participation in the molecular polarity intervention led to some long-term learning gains in students’ ability to correctly characterize polarity based on molecular formulas.
Recommended Citation
Lavoie, Cheryl, "Using perceptual learning modules to study learning of molecular polarity and visual representations in college chemistry students" (2025). Doctoral Dissertations. 2953.
https://scholars.unh.edu/dissertation/2953