Student understanding of structure-property relationships (how the molecular-level structure of a molecule affects its properties) is vital in early chemistry courses because such courses are the gateway to other sciences. Predicting the shape of a molecule accurately is essential to determining its polarity, an important concept to learn under the umbrella of structure-property relationships. To engage students in the process of predicting the shape and thereby polarity, instructors use representations that either have an explicit visual marker representing the accurate shape or sufficient information for students to deduce the shape. Researchers in this study explored the impact of four representation types: chemical formula, Lewis dot structure, ball and stick model, and space filling model. Over 1,000 students in the first-semester general chemistry course were tasked to evaluate the shape and polarity of up to 12 molecules of varying shapes. Students were randomly assigned to one of the four representations for each molecule. They were asked to predict the molecular shape, determine polarity, and select a reason for their polarity determination. The following hypotheses were tested: 1) Lewis dot structures that required deducing the correct shape hinder students in determining molecular shape and polarity, 2) ball and stick and space-filling models portray shapes accurately thereby promote students in determining polarity correctly. To test the first hypothesis, students’ responses on molecules where the Lewis dot structures explicitly demonstrates the correct shape were compared to those where the correct shape had to be deduced. To test the second hypothesis, students’ responses with ball and stick and space filling models were compared to responses for chemical formula and Lewis dot structure, including a consideration of whether two-dimensional or three-dimensional symmetry is present. Implications on the limitations of representations that hinder the learning of polarity and instructional implications for the use of representations to promote the learning of polarity will also be discussed.

Understanding the impact of representations of molecules in students’ determination of molecular shape and polarity

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.