In traditional chemistry instruction, teachers write on the blackboard, students listen, memorize the facts or rules and answer when they are asked (concisely, chalk and talk). Such learning may be seen as a ladder with too many rungs that students have to climb (overloaded curriculum). But the students often do not know why they are climbing the ladder, and fail to see the connection between adjacent rungs. Traditional chemistry education is, moreover, quite resistant to reform. But content (subject mater of knowl-edge) should be selected on a ‘need-to-know’ basis to develop coherent mental maps of chemistry knowledge and to increase the relevance of the subject (Pilot and Bulte 2006a).