Students' reasoning about basic chemical thermodynamics and chemical bonding: what changes occur during a context-based post-16 chemistry course?

A longitudinal study of 250 students following the Salters Advanced Chemistry (SAC) course probed a range of chemical ideas including the exothermicity of bond formation and the development of thinking about covalent, ionic and intermolecular bonds. Students responded to the same diagnostic questions on three occasions: at the start, after eight months and sixteen months of a twenty-month course. At the start, many students demonstrated misunderstandings about these chemical ideas, but in general their understanding improved as the course progressed. By the end of the study, about half knew that bond making is exothermic. Initially, few described covalent bonds accurately or understood hydrogen bonding. A majority gave responses at the final survey which were in line with ideas and language a chemist may use. Students attributed changes to the use of context-based materials including a drip-feed approach which allowed their understanding to develop over time. However, some aspects of chemical bonding, including ionic bonding and intermolecular bonds other than hydrogen bonds remained problematic for students despite explicit teaching. The findings have implications for post-16 chemistry teaching, suggesting that a review of teaching strategies is needed in some areas.