The connection between the molecular-level structure of a substance and its physical and chemical properties (such as boiling point or relative acidity) is an integral chemistry concept and a thorough understanding of this relationship is key to understanding larger and more complex chemistry ideas. Previous research has shown that students possess a wide range of non-normative ideas about chemical and physical properties. Student difficulties with the connection between a chemical structure and the properties of the compound, however, are far more complex than a series of misconceptions. Using a qualitative approach, we interviewed seventeen students enrolled in either general or organic chemistry courses. We found that, while many students could correctly predict and rank melting and boiling points of various compounds, few successfully used the molecular level structure of each compound to predict and explain its properties. Instead, we identified several emergent themes that categorize the ways in which students tried to explain these trends. While some students discussed similar individual ideas, no two students connected these ideas in the same manner, resulting in a wide range of interconnected, albeit fragmented, ideas. Intermolecular forces (IMFs), the forces that govern interactions between molecules based on differences in polarity and electronegativity, play an important role in this connection between structure and properties. Because few students discussed IMFs when describing the connection between structure and properties in our interviews, we designed the Intermolecular Forces Assessment (IMFA) to specifically explore students’ understanding of IMFs using questions requiring both written responses and drawn representations. This assessment was given to several groups of students at various time points at two different universities. We found that the modality of a student’s response (e.g. drawing or writing) provided different insight into student understanding. Surprisingly, students’ written descriptions of IMFs did not always align with their provided representations and analyzing the writing alone would have given a false impression of their understanding. Constructed representations, however, often provided crucial spatial information needed to determine if the students understood IMFs as occurring between molecules rather than within molecules. Using the IMFA, we also studied the effect of an alternative general chemistry curriculum, Chemistry, Life, the Universe, and Everything (CLUE), on students’ understanding of IMFs. Using two matched groups of students, those enrolled in the CLUE course and those enrolled in a traditional general chemistry course, we found that CLUE students most often correctly represented IMFs as occurring between molecules unlike the majority of students enrolled in traditional general chemistry courses who incorrectly represented IMFs as forces within a single molecule. We replicated these findings with an additional cohort of students the following year and have preliminary data that suggest these results extend to an additional university and are more generalizable. While students’ drawing can certainly be illuminating when exploring their understanding, analysis of student drawings is not always practical in terms of assessment. We investigated the use of automated text analysis of students’ IMFA responses to explore its effectiveness in determining students’ ideas about IMFs. We include preliminary findings using automated analysis of students’ written responses to attempt to predict the drawing code a student would receive for their corresponding constructed representation of a specific IMF.
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