Models play an important and central role in science as well as in science education. Chemical bonding is one of the most important topics at 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 with respect to students’ learning difficulties (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’ alternative conceptions and difficulties in understanding chemical bonding, which matched the findings found by other recent studies. Implications for textbooks’ authors and teachers are addressed.

Researchers have shown a growing interest in science teachers' professional knowledge in recent decades. The article focuses on how chemistry teachers impart chemical bonding, one of the most important topics covered in upper secondary school chemistry courses. Chemical bonding is primarily taught using models, which are key for understanding science. However, many studies have determined that the use of models in science education can contribute to students' difficulties understanding the topic, and that students generally find chemical bonding a challenging topic. The aim of this study is to investigate teachers' knowledge of teaching chemical bonding. The study focuses on three essential components of pedagogical content knowledge (PCK): (1) the students' understanding, (2) representations, and (3) instructional strategies. We analyzed lesson plans about chemical bonding generated by 10 chemistry teachers with whom we also conducted semi-structured interviews about their teaching. Our results revealed that the teachers were generally unaware of how the representations of models they used affected student comprehension. The teachers had trouble specifying students' difficulties in understanding. Moreover, most of the instructional strategies described were generic and insufficient for promoting student understanding. Additionally, the teachers' rationale for choosing a specific representation or activity was seldom directed at addressing students' understanding. Our results indicate that both PCK components require improvement, and suggest that the two components should be connected. Implications for the professional development of pre-service and in-service teachers are discussed.

Background: Textbooks are integral tools for teachers’ lessons. Several researchers observed that school teachers rely heavily on textbooks as informational sources when planning lessons. Moreover, textbooks are an important resource for developing students’knowledge as they contain various representations that in uence students’ learning. However, several studies report that students have di culties understanding models in general, and chemical bonding models in particular, and that students’ di culties understanding chemical bonding are partly due to the way it is taught by teachers and presented in textbooks.

Purpose: This article aims to delineate the in uence of textbooks on teachers’ selection and use of representations when teaching chemical bonding models and to show how this might cause students’ di culties understanding.

Sample: Ten chemistry teachers from seven upper secondary schools located in Central Sweden volunteered to participate in this study. Design and methods: Data from multiple sources were collected and analysed, including interviews with the 10 upper secondary school teachers, the teachers’ lesson plans, and the contents of the textbooks used by the teachers.

Results: The results revealed strong coherence between how chemical bonding models are presented in textbooks and by teachers, and thus depict that textbooks in uence teachers’ selection and use of representations for their lessons. As discussed in the literature review, several of the selected representations were associated with alternative conceptions of, and di culties understanding, chemical bonding among students.

Conclusions: The study highlights the need for lling the gap between research and teaching practices, focusing particularly on how representations of chemical bonding can lead to students’ di culties understanding. The gap may be lled by developing teachers’ pedagogical content knowledge regarding chemical bonding and scienti c models in general.