The conceptual difficulties faced by students on the theme "isomerism" are attributed to basic problems, such as the understanding of structural theories, chemical bonds and representations of structural formulas. This study was aimed at the evaluation of the High School stu dents' learning evolution on the isomerism phenomenon. Our strategy was based on the students' previous conceptions and on the use of the construction of concept isomers. The results have been collected from a group of twenty-five students from third grade through pre and post tri als, and were analyzed using contents analysis technique. As conclusions, it was possible to verify a conceptual evolution on the majority of the stu dents, object of this study.
Chemistry teaching; isomerism; conceptual evolution