Teaching chemical bonding through project-based learning

Resumo

The concept of chemical bonding is essential in Chemistry. Nevertheless, it is a problematic topic for students. In our particular case, we teach a Quantum Chemistry course in the second year of Chemistry Degree. Through years, we have noticed that most of our students disconnect when the long mathematical deductions involved by chemical bonding are presented in the class room. This trend did not change when we simplified these deductions, skeeping part of the process and leaving it as personal work. The relevance of the concepts involved, and their importance for following the rest of the course, prompted us to look for alternative teaching strategies. Recently, we have designed short projects to lead the students into learning these concepts. Although the projects require the whole mathematical formalism behind chemical bond in monoelectronic and bielectronic systems, we highlight that our students response has changed significantly. In fact, we have found much better results in examinations after introducing this scheme. Moreover, the students display stronger abilities in solving numerical problems and have made use of informatics tools also. The projects are based on replacing the usual textbook mathematical developments of the well-established model by alternative ones which contrast the essential ideas of chemical bonding with opposite ones. For example, whereas the simplest chemical bonding case, H-2(+) cation is presented as a linear combination of two atomic orbitals the H atom centred on each nucleus, we propose replacing them by other functions (including atomic orbitals) centred on different points. Each group of students deals with a different possibility and "investigates" if their model gives rise (or not) to a chemical bond. Worksheets implementing numerical integration methods are provided. They also receive instruction on using them. We also warn about that choosing the appropriate coordinates system simplify their mathematical task. In this way, they see how fruitful is spending some time designing strategies to make problems easier. The results are presented in a seminar with short presentations by the students. Thus, the class explores the effect of overlap, suitable/unsuitable functions, different atomic orbitals, etc.