Over the years, there has been remarkable debate among researchers in the field of teacher education about the criteria for being a qualified teacher. One of the criteria, pedagogical content knowledge (PCK), was introduced to the science education community by Shulman (1986). Shulman first conceptualized PCK as a special amalgam of content and pedagogy that guides ‘‘ways of representing and formulating the subject that make it comprehensible to others’’ (p. 9). Since the inception of PCK, researchers have proposed various PCK models (e.g., Grossman, 1990). Although these PCK models identified the components, they do not indicate how the components interact with each other (Friedrichsen, Van Driel, & Abel, 2011). Park and Oliver (2008a) stated that the components interact with each other in highly complex ways and also the interaction among the components is important for PCK development. According to the scholars, in order to effectively plan and enact instruction for a certain group of students in a specific context, teachers must be able to integrate those components into PCK in a coherent way (Loughran, Berry, & Mulhall, 2006).

Surprisingly, careful and deliberate consideration of how these components interplay with each other to structure PCK has been an unexplored issue for science teacher educators until recently (e.g. Park & Chen, 2012), considering the long history of PCK. A few scholars have recently focused on investigating the nature of interaction among all components (e.g. Park & Chen, 2012). Other research only focused on one or two components, examining how two specific components are related (e.g., Cohen & Yarden, 2009), or how the development of one component affects the whole of PCK and one's teaching practice (e.g., Matese, 2005). Therefore, research should elaborate on how teachers use PCK components coherently in order to make the topic more understandable to learners (Friedrichsen et al., 2011; Park and Chen, 2012).

With this in mind, this study explored the nature of the interplay of the five components of PCK: (a) Science Teaching Orientations (STO): teachers' knowledge and beliefs about the goals and purposes of teaching science at a specific grade level, (b) Knowledge of Learner (KoL): teachers’ knowledge about students' difficulties in learning specific topics, and misconceptions related to those topics, (c) Knowledge of Instructional Strategies (KoIS): teachers’ knowledge about science-specific strategies (e.g. Learning cycle) and strategies for specific science topics (e.g., illustrations and analogies), (d) Knowledge of Curriculum (KoC): teachers’ knowledge about both curriculum goals and curricular materials, and (e)Knowledge of Assessment (KoA): teachers’ knowledge about how to assess student performance (e.g., through portfolios or written tests) and what to assess (e.g., science process skills).  

This study was conceptually and analytically grounded in the pentagon model, which defines PCK as interplay of the five components that are mutually related to one another (Park & Oliver, 2008b). In fact, Magnusson et al.’s (1999) PCK model consisted of the same five components as the pentagon model. In addition, Magnusson et al. stated that the significance of the interplay and harmony among the components; however, their model did not reflect their ideas. Their model represented the five components in a linear way. On the one hand, the pentagon model shows the components in a pentagonal form to put emphasis on the reciprocal relation among them putting equal weight on each interplay. Accordingly, the research question guiding this study was: What is the nature of interplay among PCK components of chemistry teachers with different levels of teaching experience in chemical equilibrium topic? 

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