Many of the learning difficulties in the specific domain of chemistry are found not only in the ideas already possessed by students but in the strategic and procedural knowledge that is characteristic of everyday thinking. These defects in procedural knowledge have been described as functional fixedness and functional reduction. This article assesses the procedural difficulties of students (grade 12 and first and third year of university) based on common sense reasoning in two areas of chemistry: chemical equilibrium and geometry and polarity of molecules. In the first area, the theme of external factors affecting equilibria (temperature and concentration change) was selected because the explanations given by the students could be analyzed easily. The existence of a functional fixedness where Le Chatelier's principle was almost exclusively applied by rote could be observed, with this being the cause of the incorrect responses given to the proposed items. Functional fixedness of the Lewis structure also led to an incorrect prediction of molecular geometry. When molecular geometry was correctly determined by the students, it seemed that other methodological or procedural difficulties appeared when the task was to determine molecular polarity. The students showed a tendency, in many cases, to reduce the factors affecting molecular polarity in two possible ways: (a) assuming that polarity depends only on shape (“geometric functional reduction”) or (b) assuming that molecular polarity depends only on the polarity of bonds (“bonding functional reduction”). © 2000 John Wiley & Sons, Inc. Sci Ed 84:545–565, 2000.

Research evidence has shown that students often have views of scientific concepts that differ from those generally accepted by the scientific community. In chemistry, research on student understanding and misconceptions has been conducted in several conceptual areas. Recent studies have been carried out on misconceptions of covalent bonding and structure of molecules. According to the constructivist models of learning, the persistence of these learning difficulties could be explained because traditional teaching doesn't pose as an aim the conceptual change of students. In our opinion, it requires taking into account not only the students' previous ideas, but also the ways of reasoning they use to form their constructions.The aim of this paper is to analyze what grade 12 and university students of chemistry should "know" (declarative knowledge) and should "know how to do" (procedural knowledge, in terms of reasoning) concerning the geometry and polarity of molecules. At the same time, we try to diagnose the conceptual and procedural difficulties that the students could have to achieve meaningful learning of these chemical concepts.

We analyze how the basic concepts about atomic models are introduced into the Spanish educational system. We considered the textbooks most currently used in the educational levels from 8th FOB to the 1st University level. We finally discuss the possible sources of misconceptions.