We discuss how to reduce the incongruence between the outcomes (both cognitive and affective) of the conventional secondary chemistry curriculum and what is to be attained: the meaningful connection of students' learning to daily life and societal issues. This problem is addressed by a design study with one curriculum unit about "Water Quality". With several research cycles using developmental research, we developed an emergent understanding about an instructional framework for curriculum units that embodies a coherent "need-to-know" principle and is based on authentic practices. Using this framework we show with some other examples how a context-based chemistry curriculum can be constructed based on the developed "need-to-know" principle.

This study investigated the development of pedagogical content knowledge (PCK) within a group of 12 preservice chemistry teachers (all M.Sc.) during the first semester of their one-year post-graduate teacher education program. The study focused on PCK with respect to a central issue in science teaching, that is, the relation between observable phenomena, like chemical reactions, and macroscopic properties (e.g., boiling point, solubility) on the one hand, and their interpretation in terms of corpuscular characteristics on the other hand (macro -micro). For secondary school students, shifting mentally between the macro and micro levels is usually problematic, whereas their teachers are often unaware of students' learning difficulties in this domain. The collection of data involved two written questionnaires, interviews with each preservice teacher and their respective mentors, and an audio recording of a specific workshop session in the teacher education program. Results indicated a growing awareness among the preservice teachers concerning the need, in teaching situations, to explicitly relate the macro and micro levels to each other. Moreover, the importance of the careful and consistent use of language was noticed by many preservice teachers. The growth of PCK was influenced mostly by the preservice teachers' teaching experiences. Also, the workshop contributed substantially. Finally, for some preservice teachers, their mentors had influenced the growth of PCK. Implications for

In this article, we describe the results of a study of the pedagogical content knowledge (PCK) of preservice chemistry teachers in the context of a postgraduate teacher education program. A group of preservice teachers (n = 12) took part in an experimental introductory course module about the use of particle models to help secondary school students understand the relationship between phenomena (e.g., properties of substances, physical and chemical processes) and corpuscular entities (e.g., atoms, molecules, ions). The module emphasized learning from teaching by connecting authentic teaching experiences with institutional workshops. Research data were obtained from answers to written assignments, transcripts of workshop discussions, and reflective lesson reports, written by the participants. The outcomes of the study revealed that, initially, all participants were able to describe specific learning difficulties, such as problems secondary school students have in relating the properties of substances to characteristics of the constituent particles. Also, at this stage, all preservice teachers acknowledged the potential importance of using models of molecules and atoms to promote secondary school students' understanding of the relationship between phenomena and corpuscular entities. After teaching, all preservice teachers demonstrated a deeper understanding of their students' problems with the use of particle models. In addition, about half of the participants had become more aware of the possibilities and limitations of using particle models in specific teaching situations. Through learning from teaching, the preservice teachers further developed their PCK of using particle models, although this development varied among preservice teachers studied. © 2005 Wiley Periodicals, Inc. J Res Sci Teach 42: 947–964, 2005

Models play an important and central role in science as well as in science education. Chemical bonding is one of the most important topics in upper secondary school chemistry, and this topic is dominated by the use of models. In the past decade, research has shown that chemical bonding is a topic that students find difficult, and therefore, a wide range of alternative conceptions are developed by students. This study focuses on analyzing the models of chemical bonding in chemistry textbooks at upper secondary level and aims to investigate the content of chemical bonding presented in chemistry textbooks related to students' alternative conceptions and difficulties in understanding. Chapters concerning chemical bonding in five chemistry textbooks at upper secondary level in Sweden were analyzed. The results showed that the models of chemical bonding represented in the school textbooks might cause students to have alternative conceptions and difficulties in understanding chemical bonding, which matched the findings found by other recent studies. Thereby, the results indicate a need for filling in the gap between research and textbook writers. Implications for textbook authors and teachers are addressed.

Although there is growing interest in studies of teachers' actions and conceptions, little is known about content-related teaching problems arising in science classrooms. This article presents a case study of problems which can occur when teaching the topic of redox reactions to Grade 11 students. Two chemistry teachers, a senior and a junior teacher, were involved in the study. Their reflective comments on the teaching problems were also investigated. Research data were obtained from classroom observations and audiotaped recordings of classroom practice. After the lessons, we conducted semistructured interviews with the teachers. The teaching problems are reported in terms of teaching activities causing difficulties for students in considering new conceptions to be necessary, intelligible, plausible, or fruitful. Analyses of the teachers' comments on these teaching activities clarifies a number of reasons why they acted as they did. It can be concluded that teachers' scientific expertise is an important source of difficulties when teaching redox reactions. Implications for an improvement of current chemistry classroom practice and contentrelated teacher training are offered.