As part of a multi-institution study of student learning in inorganic chemistry, students answered questions about molecular orbital (MO) theory. While bonding has been discussed extensively in the chemistry education literature, few studies have explored student understanding of MO theory. It is important for chemistry instructors to understand student ideas about molecular orbitals. This study explored how students construct their own representations of molecular orbitals. Students were provided with an open-ended question that asked them to draw and interpret the bonding and antibonding MOs for LiH. By analyzing the identity of the orbitals used, the sign of the wavefunction, the relative contributions of different atoms, and the overall shape of the orbital, we were able to identify patterns and themes in these representations. Analysis of student drawings, collected from ~250 students at nine institutions taking a foundation course in inorganic chemistry, indicate that students do not have a complete understanding of the information conveyed by a sketch of a molecular orbital. In general, student drawings of bonding orbitals, as compared to antibonding orbitals, were more consistent with accepted models. While most students use s-orbitals in their pictures, ~15% do not attribute meaning to the sign of the wavefunction in their sketches, ~25% do not show differences in contributions of the different atoms to the MO, ~33% do not realistically represent orbital overlap, and 50% (bonding) / 67% (antibonding) do not accurately draw electron density around the two nuclei. Interpretations of these drawings, as well as recommendations for instruction, will be presented.

Student generated representations of molecular orbitals: ideas and implications for teaching

ACS Spring Meeting 2021

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