Two Models of Chemical Reactions

Abstract

This paper responses to the lack of a specific expectation on models of chemical reactions in secondary chemistry (e.g., in England and Hong Kong curriculums). It has been proposed that there are two submicro models. (a) Particle model - reactions are regarded as spatial rearrangement of simple particles. This model is commonly likened to rearrangement of Lego blocks. (b) Atomic model - reactions involve specific particles such as ions, atoms, molecules and electrons. The Lego analogy breaks down in this model because particles would change, say, from ions to molecules or from atoms to ions (cw. individual Lego blocks remained unchanged in spatial rearrangement). This paper reports results from a cross-sectional- and a 2.5-year longitudinal project that investigated Grades 10-12 students’ submicro representations of chemical reactions. It was found that students were adept at representing chemical reactions as the particle model – to the extent that they adopted this model for redox reactions, which should be represented more usefully by the atomic model. Also, this presentation conceptualizes variations within individual students as they represented the same reaction in different occasions (after they were taught acid/base reactions, electrochemistry, and at the end of their secondary schooling respectively). Instead of treating their representations as misconceptions or failure to learn, their preference for the particle model could be regarded as resources for the teaching of the atomic model. Implications for research and classroom practice based on the longitudinal data will be discussed.