The topic-specific nature of experienced chemistry teachers’ pedagogical content knowledge in the topics of interactions between chemical species and states of matter

Abstract

This study aims to determine the topic-specific nature of two experienced chemistry teachers’ pedagogical content knowledge (PCK) in the topics of interactions between chemical species and states of matter. The teachers’ PCK on these topics was investigated in terms of the following components: orientations toward science teaching (OST), knowledge of curriculum (KoC), knowledge of instructional strategies (KoIS), knowledge of learner (KoL), and knowledge of assessment (KoA). Data for the study were collected over five months using multiple data collection tools, including semi-structured interviews, observations, card-sorting activity, and field notes. PCK is identified in the literature as a topic-specific knowledge. Similarly, chemistry teachers’ PCKs in this study were found to be topic-specific in the topics of interactions between chemical species and states of matter. However, it was seen that some dimensions of the PCK components were not topic-specific. The results indicated that one of the participants’ OST was topic-specific, while the other's was not topic-specific. Further, it was determined that the participants focused on abstract nature in the topic of interactions between chemical species, but they focused on daily life examples in the topic of states of matter. To overcome the students’ difficulties and misconceptions, the participants highlighted abstract nature in the topic of interactions between chemical species and familiar examples in the topic of states of matter. Their KoC differed in terms of relations with other disciplines and curriculum sequence across the topics. Lastly, it was found that the participants’ KoAs consisted of general pedagogical knowledge for both topics. In the light of the results of this study, implications are stated and suggestions on improving the understanding of the topic-specific nature of PCK are provided for in-service chemistry education, pre-service chemistry teacher education, and chemistry education researchers.

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Introduction

Effective teaching is a mentally and physically challenging and demanding process, one that can only capably and thoroughly be performed by teachers who are equipped for the task (Shulman, 2015). When a classroom environment is observed from the outside, it is difficult to understand just how complex the underlying knowledge of instructional decisions can be, and often times, the failure to understand this makes it appear that the teaching carried out by the teacher is quite simple (Bransford et al., 2005), However, given the complex nature of teaching and the wide range of knowledge and skills it requires, the process of learning how to teach should be viewed as one that lasts a lifetime (Nilsson and Elm, 2017; Schneider and Plasman, 2011).

Cultivating teachers who possess a strong base of knowledge and make reliable decisions about their teaching by applying this knowledge base is becoming increasingly more important in contemporary societies (Bransford et al., 2005). In turn, the challenging task of identifying, classifying, and documenting teachers’ professional knowledge is also becoming increasingly more important (Berry et al., 2008). Although concepts related to the type of knowledge distinguishing teachers from field experts have been cited in earlier teacher education studies, the concept of pedagogical content knowledge (PCK), which refers to the knowledge type specific to a subject field, has gained wide appeal after being first introduced by Shulman (1986).

Shulman and succeeding researchers have defined PCK as a topic-specific knowledge type (Abell, 2008; Akın and Uzuntiryaki-Kondakci, 2018; Cooper et al., 2015; Magnusson et al., 1999; Mthethwa-Kunene, 2014; Park and Suh, 2015; Sande, 2010). In contemporary science education research literature, little attention is given to investigating topic-specific PCK within the same discipline (Abell, 2008; Lankford, 2010). Investigating this kind of PCK, through a holistic lens, is critically important, because it could provide insight into how topic-specific PCK develops (Aydin, 2012; Aydin et al., 2014; Sande, 2010). For this reason, further studies are needed to examine how the topic-specific nature of PCK is applied in real classrooms (Stender et al., 2017). PCK can be influenced by many factors; teaching experience is one factor that influences a teacher's PCK. According to Barnett and Hodson (2001), experienced teachers have more accessible and useful knowledge than pre-service and novice teachers. Since pre-service or novice teachers usually have limited PCK (Aydin and Boz, 2012; De Jong and van Driel, 2001; Lee et al., 2007), studies of experienced teachers might provide richer examples of teachers’ PCK and how they apply their PCK in the classrooms (Aydin et al., 2014). Despite the impact of experience on teachers’ PCK, most studies focus on examining pre-service teachers’ PCK (Abell, 2007; Aydin and Boz, 2012). To fill these gaps in the literature, this study aimed to determine the PCK of experienced chemistry teachers in the topics of interactions between chemical species and states of matter in real classrooms. To provide a holistic view of PCK, the current study intended to examine teachers’ PCK in terms of all five components suggested by Magnusson et al. (1999). The research question of this study was as follows:

“To what extent is the PCK of experienced chemistry teachers in the topics of interaction between chemical species and states of matter topic-specific?”

Theoretical framework

When Shulman first introduced PCK, it caused a paradigm shift in educational studies, and since its development in the 1980s, many researchers have adopted and developed this concept as the framework for their studies, as it has been supported by theoretical developments and empirical studies (Evens et al., 2015). The PCK model suggested by Magnusson et al. (1999) has been preferred by many researchers, particularly those conducting science education studies (Aydin and Boz, 2012; Aydin et al., 2014; Evens et al., 2015; Scharfenberg and Bogner, 2015), as it provides a handy systematic approach and a reliable framework capable of characterizing the individual PCK components from the unified perspective of the knowledge possessed by science teachers (Abell, 2007; Soysal, 2018). According to Abell (2008), the discrete components of this model can serve as useful tools for science researchers. Moreover, there are studies (e.g., Aydin et al., 2014; Chen and Wei, 2015; Hanuscin et al., 2011), on several topics that provide empirical support to use the transformative PCK model proposed by Magnusson et al. (1999). PCK is defined as a synthesised knowledge base for teaching in the transformative model. According to this model, content and pedagogy are integrated and transformed into classroom practice (Lee and Luft, 2008). Since experienced teachers can simultaneously use all domains of knowledge together (Ball and Bass, 2000; Davis, 2003; Grossman, 1990), the transformative PCK model is better able to represent experienced teachers’ PCK (Lee and Luft, 2008). Based on these reasons, we used the PCK model of Magnusson et al. (1999) in the current study. The model proposed by Magnusson et al. (1999) addresses PCK in terms of science education and states that PCK consists of five components: orientation toward science teaching (OST), knowledge of curriculum (KoC), knowledge of instructional strategies (KoIS), knowledge of learner (KoL), and knowledge of assessment (KoA).

According to Magnusson et al. (1999), PCK is a type of topic-specific knowledge. Similarly, PCK is defined as topic-specific professional knowledge in the new consensus model of PCK (Gess-Newsome, 2015). Moreover, PCK is defined as context-specific and PCK-in-action and PCK-on-action are differentiated in this new model. It is stated that PCK-on-action is the knowledge of, reasoning behind, and planning for teaching a particular topic. On the other hand, PCK-in-action is defined as the act of teaching a particular topic. According to Gess-Newsome (2015), PCK-on-action can be found in teachers’ instructional plans and the reasons behind their instructional decisions, but PCK-in-action can be captured by classroom observations. The new consensus model had not yet been published when the present study was designed and the data collected and analyzed. However, this new model includes components similar to the components in Magnusson et al.'s (1999) PCK model. Moreover, the present study used multiple data collection tools to try and capture both PCK-on-action and PCK-in-action, which are mentioned in the new consensus model of PCK.

In this study, the PCK model proposed by Magnusson et al. (1999) was modified in light of the related literature. In addition to Magnusson et al.'s (1999) nine orientations, exam-focused OST (Aydin et al., 2014) was added as a sub-dimension of OST. Purpose of assessment (Aydin et al., 2014) was added as a sub-dimension of KoA. Additionally, vertical and horizontal relations (Grossman, 1990) and altering the curriculum sequence (Friedrichsen et al., 2007) were added as sub-dimensions of KoC.

Literature review

A review of the science education studies showed that the topic-specific nature of PCK has been addressed in two ways: (i) for a single topic, and (ii) for multiple topics. For example, Geddis et al. (1993) examined the topic-specific nature of PCK for a single topic (isotopes) and reported that an experienced chemistry teacher tried to have the students achieve the objectives of the curriculum. In another study, Okanlawon (2010) investigated chemistry teachers’ PCK in reaction stoichiometry. The results of the study indicated that the teachers generally had a didactic OST and focused on solving numerical problems. Sande (2010) examined experienced chemistry teachers’ PCK in the topic of gas laws and found that the chemistry teachers explained gas laws using daily life examples. In another study, Rollnick and Mavhunga (2014) reported that most of the experienced chemistry teachers had insufficient KoL in the topic of electrochemistry.

Unlike the studies that concentrated on the topic-specific nature of PCK for a single topic, Aydin et al. (2014) investigated the topic-specific nature of PCK for two topics (electrochemical cells and nuclear reactions). They found that the chemistry teachers’ PCK in the topic of electrochemical cells was content-based and teacher-centered. In the topic of nuclear reactions, the results of the study showed that the participants’ PCK was less teacher-centered.

Significance of this study

Examining the PCK studies (e.g.Friedrichsen et al., 2009; Henze et al., 2008; Park and Chen, 2012; Rollnick et al., 2008) in Van Driel et al.'s (2014) review, it is seen that PCK has been investigated within a single topic and that only some components of PCK were examined in most of these studies. On the other hand, an effective teacher needs to develop knowledge of all of the topics she/he teaches, and all the components of PCK (Magnusson et al., 1999). Therefore, it is important to examine a teacher's PCK in multiple topics and in terms of all components of her/his PCK. With this in mind, the topic-specific nature of chemistry teachers’ PCK in this study was investigated for two topics, the first of which is interaction between chemical species. This topic is fundamental to the teaching of chemistry and directly related to the understanding of many chemistry concepts. Moreover, this topic involves several chemistry concepts and has proved very complex for teachers to regulate and apply (Tsaparlis et al., 2018). The second of the two topics examined is states of matter. This topic is one of the chemistry topics that students fail to understand. Furthermore, this topic is crucial, since it has some roles to explain real-life and environmental problems. Moreover, it is related to other chemistry topics, such as particulate nature of matter, physical and chemical changes, and chemical bonds (Ayyıldız and Tarhan, 2013). Since they possess such characteristics, this study examined chemistry teachers’ PCK in these topics. In addition, there were only a very limited number of studies investigating PCK in terms of all the components suggested by Magnusson et al. (1999) that is OST, KoIS, KoL, KoC, and KoA. By investigating all components for PCK of chemistry teachers working in public schools in two topics (interactions between chemical species and states of matter), something that has not been done before, within the same discipline through a holistic approach, this study may provide critically important information in terms of understanding the structure of PCK components and the topic-specific nature of PCK.

It is crucial to examine experienced teachers’ PCK to guide the training of pre-service and novice teachers (Henze et al., 2008; Schneider and Plasman, 2011). Considering that in science education, PCK can be best represented within studies conducted with experienced science teachers, those experienced science teachers who frequently discuss instruction may be able to shed some light on PCK (Lee and Luft, 2008). Unlike numerous PCK studies conducted with pre-service teachers, this study was conducted with experienced chemistry teachers having more than five years of professional experience because it is thought that studying with experienced chemistry teachers in real classroom environments provides PCK researchers with reliable information to understand PCK in action.

Methodology

This study took the form of a qualitative case study. Case studies are a type of qualitative research design wherein one or several cases are subjected to an in-depth holistic analysis without any intervention and questions as to why and how are investigated (Creswell, 1994; Yin, 2003). The subject of this particular case study is the topic-specific nature of two experienced chemistry teachers’ PCK in the topics of interactions between chemical species and states of matter.

Participants

The public schools where this study was conducted were selected using the convenience sampling technique. In the convenience sampling technique, the participants are selected based on time, location, money, and availability (Merriam, 2009). It was decided to conduct this study at two public schools in the same district. After choosing the public schools, the criterion sampling technique, a purposeful sampling method (Patton, 2002), was used to select the participants. The professional experience of teachers was used as the criterion in the current study. Berliner (2001); Martin et al. (2006) suggested that teachers should have at least five years of experience to be described as experienced teachers. For this reason, it was decided that the present study should include high school education chemistry teachers with professional experience of more than five years to investigate the topic-specific nature of PCK. Accordingly, the present study involved two experienced chemistry teachers. Zeynep (female) and Mehmet (male) with 21 and 8 years of teaching experience, respectively. The participants taught at the public schools. They had graduated from the chemistry education program and were certified as chemistry teachers for grades 9–12. Zeynep had a master's degree in chemistry education. Mehmet was still studying for his master's degree in chemistry education at the time of this study.

Context of the study

Compulsory nation-wide exams play an important role in the educational system in which this study was carried out. To be admitted to a university program, students have to, at the end of high school, take an entrance exam. These exams have impact on the curriculum and on teachers. Teachers are expected to adhere to the time specified in the curriculum for each topic while implementing it, and are asked to adhere to the objectives and special warnings of the curriculum. A such, teachers experience time constraints and constraints regarding the content of their lessons.

The schools where Zeynep and Mehmet worked are located in a large city in the country. They have similar instructional materials and technical equipment (e.g. laboratory, library, computers, smartboards, blackboards, conference room). Zeynep's class sizes ranged from 30 to 40 students. Mehmet's class sizes ranged from 20 to 25 students. The students’ ages ranged between 16 and 18 in both schools.

Ethical considerations

The necessary approvals relating to the conduct of this study (i.e. rights of teachers participating in the study and data collection) were obtained from the Ministry of National Education. Before conducting the study, the participants were informed about the process of the study and told that their participation was strictly on a volunteer basis and that they could withdraw from the study at any time they wished. All teachers participated in the study voluntarily. In this study, pseudonyms were used to keep the participating chemistry teachers’ identities confidential. In addition, the names of the public schools where the study was carried out were kept confidential.

Data collection tools

Park and Suh (2015) argued that due to the complicated nature of PCK, multiple measurements should be made to evaluate teachers’ PCK. Several instruments (interviews, observations, field notes, card-sorting activities, Content Representations (CoRes), Pedagogical and Professional experience Repertoires (PaP-eRs), and tests) have been successfully used to measure the topic-specific nature of PCK (Akın and Uzuntiryaki-Kondakci, 2018; Aydin et al., 2014; Henze et al., 2008; Mavhunga, 2016). In this study, we aimed to capture both PCK-in-action and PCK-on-action. Semi-structured interviews and card-sorting activities were used to determine teachers’ PCK-on-action, while PCK-in-action was captured via observations and field notes. The data collection tools and the participants’ statements were translated into English from another language.

The examples of the data collection tools are given in Appendix. The data collection process of the study is shown in Table 1.

Table 1 Data collection process of the study

Stages	Data collection process
Prior to teaching the topics	– Conducting pre-interviews with chemistry teachers on teaching chemistry
During ‘Interactions between chemical species’ and ‘States of matter’	– Card-sorting activity (at the beginning of the topic)
	– Observing lessons (throughout the topic)
	– Conducting weekly interviews (throughout the topic)
After teaching the topics	– Conducting interviews with the teachers on the two topics

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Observations and field notes. The participants’ lessons on two topics were observed three hours a week in their classrooms using a semi-structured observation form. During the observation of the teachers’ lessons, field notes were taken. The observation sessions were recorded with a camera. Field notes were taken regarding PCK components. For example, some points in the semi-structured observation form for KoL are:

“The teacher checks the student's pre-requisite knowledge about the topic.”

“The teacher knows that the students are having difficulties with the topic.”

“The teacher is aware of the potential misconceptions in the topic.”

“The teacher warns the students about known misconception in the topic.”

Interviews: semi-structured interviews were conducted with the teachers at different stages of the research process. These interviews lasted between 15–40 minutes. Studies in the literature (Aydin et al., 2014; Magnusson et al., 1999) were referred to when writing the semi-structured interview questions. Throughout the study, the interviews with the teachers were recorded with an audio recorder. Prior to the teaching of the topics, a pre-interview was conducted with the participants. In this interview, questions focused on the teachers’ demographic characteristics and their views on teaching chemistry.

When the participants taught the topics of interactions between chemical species and states of matter, weekly interviews were conducted with them on the lessons for that week and the lessons were observed. After the teaching of both topics was over, final interviews were conducted with the participants to have them compare how both topics were taught.

Card-sorting activities: the card-sorting activity was a data collection tool used to identify the OST that the teachers possessed to teach science to their students (Friedrichsen and Dana, 2003). This study had its participants perform the card-sorting activities for both topics to examine the OST component of PCK. Studies in the literature (Aydin et al., 2014; Friedrichsen, 2002; Friedrichsen and Dana, 2003) were referred to when writing the scenarios for the card-sorting activities. An example of a scenario used for academic rigor orientation was: “One way to teach bond energies effectively is to pose difficult and challenging questions for students”. An example of a scenario used for discovery orientation was: “One way to teach the effect of temperature on viscosity effectively is to plan an investigation for students that let them discover the viscosities of substances at different temperatures”. Participants were asked to sort scenario cards into three groups – best represents his/her teaching, does not represent his/her teaching, and unsure. Moreover, participants were asked to explain the characteristics of scenarios chosen from a group of cards.

Chemistry topics examined in this study

When this study was conducted, the participants taught in the 10th grade. The chemistry curriculum for the 10th grade was based on the constructivist approach. The content in the curriculum was prepared with a perspective that enables students to construct the knowledge themselves. Teachers are asked to prepare daily and annual plans based on the goals and objectives of this curriculum. In addition, they are asked to evaluate students’ higher-order thinking skills, such as solving problems encountered in daily life or making inferences based on observations. Therefore, it is suggested that teachers use both traditional assessment methods (e.g. multiple-choice tests, true/false questions, and open-ended questions) and alternative assessment methods (e.g. concept maps, performance tests, and portfolios) to assess students’ understanding. At the time this study was conducted, the 10th-grade chemistry curriculum included units on atomic structure, the periodic table, interactions between chemical species, states of matter, and mixtures. Interactions between chemical species and states of matter were chosen to examine participants’ PCK. Interactions between chemical species included chemical species, interactions between these species, strong interactions, and weak interactions. An example of learning outcomes stated in the curriculum for this topic was: “The student can explain the formation of metallic bonding”. States of matter included properties of gases, ideal gas laws, mixtures of gases, real gases, properties of liquids, changes between states of matter, non-crystalline solids, and crystalline solids. An example of learning outcomes stated in the curriculum for this topic was: “The student can examine the pressure–volume relationship of a certain amount of gas at a constant temperature (Boyle's law)”. The times stipulated in the curriculum for the topics of interactions between chemical species and states of matter were 20 hours and 24 hours, respectively. In addition, the activities that the teachers were expected to use when teaching these topics were included in the curriculum. For example, in the curriculum, the teacher was asked to use interactive virtual experiments during the teaching of ideal gas laws. Moreover, the teacher was asked to assess students’ understanding by using these interactive virtual experiments in the curriculum. Students were asked to derive formulas about pressure, volume and temperature using the results they have obtained via these interactive virtual experiments. In addition, students were expected to solve problems using these formulas. In another example in the curriculum, the teacher was asked to make an experiment in which her/his students could determine the surface tensions of ethyl alcohol and water.

Validity and reliability

In this study, long-term interaction (five months) and data triangulation (observations, interviews, and card-sorting activities) were employed for credibility. Consistency was achieved this way throughout the study. For confirmability, in addition to data triangulation, a chemistry educator whose dissertation was on chemistry teachers’ PCK conducted a peer examination by checking the stages related to the research process, data collection tools, data analysis, and interpretation of the results.

In this study, organizing the data obtained under themes and categories, supporting the data with direct statements, producing in-depth descriptions, describing the schools and classrooms in a detailed manner, and the criterion sampling technique were the methods used to increase transferability.

Data analysis

In this study, the data were first transcribed, and then the observation notes and interview transcriptions were read. Raw codes were developed. The codes derived from the data at the analysis stage were also added to the code list. Similar parts were collected under the same codes. The data were read at length several times, and coding was checked. After completing the coding process, the codes were collected by theme considering their common properties and their relationship with each other. The results were described in detail, supported by direct statements, and interpreted by the researchers. The raw data, data coding, and determination of themes were checked by a chemistry education expert who had conducted studies on PCK. To verify the consistency between the analyses conducted by the chemistry educator and the researchers, the formula [Agreement/(Agreement + Disagreement) × 100] suggested by Miles and Huberman (1994) was used. The results from this formula revealed a consistency of 91%. The disagreement was resolved by a consensus reached between the researchers and the chemistry educator. Examples of categories used in data analysis and their explanations were given in Table 2.

Table 2 Examples of the categories used in data analysis

Components of PCK	Categories	Explanation
OST	Teacher-centered OST	Teacher considers preparing students for the university entrance exam as the focus of her/his teaching of the topic. She/he often emphasizes the points of the topic that may be asked in the university exam and solve questions asked in these exams in previous years.
		Teacher applies lecture-based teaching approaches throughout her/his teaching of the topic. She/he often uses the question-answer technique. She/he acts as a knowledge transmitter.
KoA	General and traditional	Teacher uses traditional assessment methods to elicit students’ prior knowledge and understanding. She/he carries out diagnostic and formative assessments for a few students. Furthermore, summative assessment was carried out for the entire class. She/he judges the students’ understanding based on written test results.

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Results

In this part, the results for the topic-specific nature of the participants’ PCK in the topics of interactions between chemical species and states of matter are presented in terms of PCK components. These results are supported by direct statements from the participants. The participants’ PCK in both topics are presented separately for each participant in Tables 3 and 4. Moreover, the results obtained by card-sorting activities are given in Table 5.

Table 3 Zeynep's PCK in both topics

PCK components	Interactions between chemical species	States of matter
OST	Between student- and teacher-centered OST	Teacher-centered OST
KoC	Limited relations with other disciplines and following the curriculum sequence	More relations with other disciplines and altering the curriculum sequence
KoIS	Instruction based on embodying the abstract nature	Instruction based on daily life examples
KoL	Highlighting abstract nature	Highlighting familiar examples
KoA	General and traditional	General and traditional

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Table 4 Mehmet's PCK in both topics

PCK components	Interactions between chemical species	States of matter
OST	Teacher-centered OST	Teacher-centered OST
KoC	Limited relations with other disciplines and following the curriculum sequence	More relations with other disciplines and altering the curriculum sequence
KoIS	Instruction based on embodying the abstract nature	Instruction based on daily life examples
KoL	Highlighting abstract nature	Highlighting familiar examples
KoA	General and traditional	General and traditional

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Table 5 The results obtained by card-sorting activities

Scenarios in the card-sorting activity	Zeynep						Mehmet
	Interactions between chemical species			States of matter			Interactions between chemical species			States of matter
	i	ii	iii	i	ii	iii	i	ii	iii	i	ii	iii
i: “best represents how I would teach”, ii: “does not represent how I would teach”, iii: “unsure”.
Academic rigor			+			+		+			+
Activity-driven		+		+				+			+
Conceptual change	+			+			+			+
Didactic	+				+		+			+
Discovery		+				+	+				+
Guided-inquiry	+			+			+				+
Inquiry	+			+			+			+
Process	+			+			+			+
Project-based		+			+		+				+

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Orientations toward science teaching

According to the results of this study, in terms of OST, it was found that the OSTs revealed by the card-sorting activities were different from the OSTs revealed by the in-class observations. Although the participants talked about student-centered scenarios in the card-sorting activity, these OSTs were not observed in the participants’ lessons. In other words, their ideal OSTs were different from their working OSTs for both topics. When participants were asked about the reason for this difference; they stated that the curriculum was very loaded and they had to complete the curriculum on time, because of the pressure of the university entrance exam. They also stated that they had parental pressure on preparing students for the university entrance exam. For these reasons, they said that they could not use student-centered OSTs during their lessons even though they thought that these orientations were more effective.

In terms of observed OSTs, it was seen that the participants had multiple OSTs for both topics. Zeynep's OSTs differed depending on the topic. Her OSTs were between student- and teacher-centered for the topic of interactions between chemical species. On the other hand, she was observed to use teacher-centered OSTs for the topic of states of matter. Conversely, Mehmet's OSTs were not topic-specific. His OSTs were found to be teacher-centered for both topics.

Between student- and teacher-centered OST. While Zeynep's OSTs were didactic and exam-focused, in other words, teacher-centered, for the topic of states of matter, while her OSTs were more student-centered for the topic of interactions between chemical species. It was determined that Zeynep had a guided inquiry OST, also known as a student-focused OST, for the topic of interactions between chemical species. Zeynep asked questions to the students to start the inquiry process. It was seen that there were no hands-on activities in the inquiry process carried out by Zeynep. She conducted this process by applying only minds-on activities. In addition, she always asked her students to inquire and encouraged students with different opinions to explain them during these inquiries. A sample of one of the dialogues that took place during these discussions in Zeynep's lessons is provided below:

Zeynep: In a molecule like XY, by how much percent do the jointly used electrons stay in the atom X and Y? For example, in a water molecule, the jointly used electrons stay in the oxygen by 50% and in the hydrogen by 50%? In your opinion, what determines this?

Student 1: It changes based on the electronegativity.

Zeynep: Well, how does it change?

Student 1: For example, since the electronegativity of oxygen is three, electrons orbit it more than they do hydrogen. However, they also travel around the hydrogen. For example, let's say that they travel around the oxygen for three hours; in that case, they would travel around the hydrogen for one hour.

Zeynep: The electron mostly stays in the oxygen, right?

Student 1: Yes.

Zeynep: Your friend proposes that the electron stays for a longer time in the atom with a greater electronegativity. Does it make sense?

Student 2: It makes sense to me.

Zeynep: Why does it make sense? Based on what? How do you defend it? I asked in which atom the electron stays longer.

Student 3: In the bigger atom, the one with a greater radius.

Zeynep: Your friend also said the one with a greater electronegativity. Then, you should say no, if it stays in the one with a greater radius.

Student 2 and Student 3: It will stay longer in the atom with a greater electron radius.

Zeynep: Is this your idea? You bring forward an idea. What is the basis of your idea? Your idea could be correct or incorrect. Why do you think like this, what leads you to think like that? This is what interests me the most… (Observation, January 17, 2013)

Teacher-centered OST. Exam-focused OST is the OST that was predominantly observed for both topics. The participants continuously reminded their students of the university entrance exam and made regular mention of the questions that could be asked in this exam and they perceived preparing their students for the university entrance exam to be one of the primary purposes of teaching chemistry. They also added, however, that the university entrance exam constrained them, that they were forced to be exam-focused and that the university entrance exam influenced their decisions with respect to teaching, even though they were not pleased about this. Zeynep's and Mehmet's explanations regarding this issue are given below:

Zeynep: It is important that students understand the topic. However, since students also think of the university entrance exam, it is more important for them to solve test questions that may appear in this exam. (Interview, May 16, 2013)

Mehmet: The topic of interactions between chemical species is important, one on which there will be questions in the university entrance exam. (Interview, February 25, 2013)

The university entrance exam influenced both participants’ lessons for both topics. They emphasized the most likely points to be asked in this exam. After teaching the topics, the participants solved the questions asked in university entrance exams in previous years. For example, Zeynep spent two class hours solving these questions. Zeynep's explanation to her students is given below:

Zeynep: …Now we will solve questions asked on this topic in university entrance exams in previous years. Please listen carefully and try to understand, because similar questions may be asked again… (Observation, March 18, 2013)

In addition to the exam-focused OST, Mehmet had didactic OST for both topics. He always used the lecturing method. Mehmet's statements on how he conducted his lessons are given below:

Mehmet: My lessons are mostly lecture-based, where students take notes and solve example problems. This is generally the flow of my lessons. (Interview, March 11, 2013)

While Mehmet's OST on both topics was didactic, Zeynep's OST was didactic only in the topic of states of matter. She assumed the role of being a knowledge transmitter on this topic, performing her lessons through lecturing. It was observed that Zeynep deviated from the way of teaching she typically used for the topic of interactions between chemical species to complete the curriculum on time and to allocate more time for the next topic (mixtures). Her opinions regarding this style of teaching are given below:

Zeynep: Since I felt behind schedule in completing the curriculum, I felt rushed to get to the topic of mixtures, which is the topic after states of matter. That's why I taught the topic of states of matter in a didactic way. (Interview, May 16, 2013)

To summarize, both participants mostly had an exam-focused OST for the topics of interactions between chemical species and states of matter. Furthermore, while Zeynep applied guided inquiry for the topic of interactions between chemical species and had a didactic OST for the topic of states of matter. Mehmet had a didactic OST for both topics.

Knowledge of curriculum

When comparing participants’ KoC for both topics, it was identified that participants’ KoC were varied in some respects. For both topics, they had a rich knowledge of the objectives, the special warnings in the curriculum, and the vertical and horizontal relations in the curriculum. In other words, they were aware of the objectives and special warnings stated in the curriculum for both topics. Mehmet offered the following thoughts on this matter in the interview conducted after the lesson:

Mehmet: My target was to have the students gain the objectives stated in the curriculum… The targets of teachers cannot be different from these objectives… (Interview, February 25, 2013)

The participants took into consideration the special warnings stated in the curriculum during their lessons. Zeynep's explanation to her students about one of the special warnings for the topic of states of matter in the curriculum is given below:

Student: Are we going to address the topic of manometers, my teacher?

Zeynep: Your curriculum does not include the manometers; you will be introduced to manometers in the physics lessons. (Observation, May 13, 2013)

When teaching the topics, the participants presented vertical relations to help the students remember their chemistry knowledge from previous years and to prepare them for the following chemistry topics. The participants frequently showed the students how the topic of interactions between chemical species linked to chemical bonding, a ninth-grade topic. Moreover, the participants presented horizontal relations by establishing connections with the previous chemistry topics learned at the same grade level.

In contrast, their KoC varied in terms of relations with other disciplines and curriculum sequence across the two topics. In the topic of interactions between chemical species, they formed limited relations with other disciplines and followed the curriculum sequence. However, they used more relations with other disciplines and altered the curriculum sequence in the topic of states of matter.

Limited relations with other disciplines and following the curriculum sequence. The participants formed limited relations with other disciplines for the topic of interactions between chemical species. They linked the topic of interactions between chemical species to the topics in physics. Zeynep's presentation of how this topic is related to the physics subject is given below:

Zeynep: If the radius is small, the electrostatic gravity force between ions increases and the strength of the ionic bond increases. Why does the strength of the ionic bond increase as the charge increases? There was a formula we used in physics; do you remember it, Coulomb's law of gravitation? (Observation, February 19, 2013)

Moreover, Zeynep and Mehmet adhered perfectly to the curriculum in every aspect of the interactions between chemical species. For this topic, they followed the sequence stated in the curriculum.

More relations with other disciplines and altering the curriculum sequence. The participants connected the topic of states of matter to topics in physics, biology, mathematics, geography, and astronomy. A few examples of the multi-disciplinary relations presented to the students by the participants included relating Graham's law of effusion to kinetic energy, which the students learn in physics; explaining relative humidity through geography; and referring to mathematics when using direct and inverse proportion in the ideal gas laws. An example of how Zeynep used relations with other disciplines is given below:

Zeynep: You have seen the topic of relative humidity in the geography. What do you remember about relative humidity from geography?

Student 1: If the relative humidity is 100%, it rains.

Student 2: It depends on temperature.

Zeynep: Relative humidity is the ratio of the partial pressure of water vapor in the air to the equilibrium vapor pressure of water at the same temperature. (Observation, April 15, 2013)

For this topic, the participants made some changes in the curriculum that altered its sequence and that ignored its special warnings. Zeynep explained her reason for altering the curriculum sequence as follows:

Zeynep: …I felt like I needed to start addressing vapor pressure. Normally, this concept would be addressed later, but, since the students did not know about boiling and evaporation, I felt the need to mention vapor pressure. It was within the curriculum but scheduled for later, so I altered the sequence. (Interview, April 25, 2013)

In addition to altering the curriculum sequence, the participants sometimes touched on concepts related to states of matter that were not included in the curriculum. For example, although manometers are included in the physics curriculum, Mehmet strayed from the chemistry curriculum and taught manometers. He stated that he included manometers in his teaching because physics teachers are not sufficiently capable of teaching this, as it is a concept that has only recently been incorporated into the physics curriculum, and there are questions about manometers in the university entrance exam.

In summation, the participants were aware of the objectives and the special warnings in both topics and they presented vertical and horizontal relations in their lessons. Furthermore, they presented limited relations with other disciplines for the topic of interactions between chemical species and more interdisciplinary relations for the topic of states of matter. Moreover, they followed the curriculum sequence for the first topic, but they altered the curriculum sequence for the second topic.

Knowledge of instructional strategies

When comparing participants’ KoIS for two topics, it was found that participants did not use science-specific strategies in either of the topics. Moreover, it was determined that the topic-specific strategies used by the participants were different for both topics.

Science-specific strategies. The participants did not use science-specific strategies in either of the topics but frequently used either the lecturing method or the question-answer method to teach the topics. They generally asked a couple of questions on the topics at the beginning of the lesson before starting the lecture. After the lecture, they addressed the students’ questions or had their students solve numerical problems. It is stated that inquiry-based learning, the 5E instructional model, and the process of conceptual change can be used specific to science (Aydın et al., 2013; Aydin et al., 2014; Lee et al., 2007; Magnusson et al., 1999). In this study, the participants did not use any of these strategies. In other words, the teaching strategies that the participants used for both topics were not science-specific strategies; rather, they were general strategies that could be used in any discipline.

Topic-specific strategies. “Instruction based on embodying abstract nature” was used for teaching the topic of interactions between chemical species and “instruction based on daily life examples” was used to teach the topic of states of matter.
Instruction based on embodying abstract nature. To teach the topic of interactions between chemical species, the participants tried to have their students envision the particulate nature of matter and embody this topic for their students. To do this, they included topic-specific analogies in their lessons. For example, to teach electron distribution, Zeynep used the analogy of a solar system, associating the sun with the nucleus of the atom and the planets with the electrons. In another example, when teaching metallic bonds, Mehmet associated the positive charges with an island, negative charges with the sea and justified that he made this association for the sake of embodying. However, during the use of analogies, the participants did not indicate the similar and different features of the analogs and target concepts in their analogies and did not follow the stages of a model (such as Teaching-With-Analogies). Zeynep's and Mehmet's explanations about the analogies used by them are given below:

Zeynep: Since atoms are at the microscopic level, I tried to carry them to macroscopic level… (Interview, January 10, 2013)

Mehmet: When teaching metallic bonding, I used an example of an island and the sea. I did this to make it easier for students to understand the metallic bonding by embodying it. (Interview, March 04, 2013)

In addition to analogies, Zeynep used role-playing and Mehmet used molecule models (ball-stick models) to embody the abstract nature of the topic of interactions between chemical species. Since Mehmet did not provide enough explanation when using the models and did not have any of his students interact with the models; his use of the model was ineffective. Generally, Zeynep applied the role-playing strategies to explain abstract concepts (e.g. atoms, molecules, and ions) related to chemical species that the students struggled to grasp. However, she did not follow the stages of role-playing in this process; that is, she did not explicitly explain the purposes of the role-playing or the students’ roles, and there were no discussions after the process of role-playing. In other words, the implementation of the role-playing had some deficiencies and was not sufficiently effective. Zeynep's explanation of her use of role-playing is given below:

Zeynep: As the particles involved in the topic of interactions between chemical species are so small, I used role-playing… When students can visualize an idea, they can comprehend it more easily. (Interview, May 16, 2013)

In summation, participants used topic-specific strategies to embody the abstract nature of the topic of interactions between chemical species. However, the topic-specific strategies used by them were poor and not effective enough.

Instruction based on daily life examples. Daily life examples were the most frequent topic-specific strategies used by both Zeynep and Mehmet for the topic of states of matter. For example, they used the idea of a pressure cooker in explaining Gay-Lussac's law and the idea of a hot air balloon in explaining Charles's law. In another example, when explaining pressure, they referred to the balance between air pressure and blood pressure. Moreover, they gave examples of insects walking on the surface of water to explain the surface tension. Excerpts about the daily life examples used by the participants are given below:

Zeynep: We're not aware right now, but millions of gases hit us constantly. However, we do not feel the pressure of the air. Our blood pressure balances out air pressure. Our skin is like a vessel with piston. (Observation, March 27, 2013)

Mehmet: If I take a ball having constant pressure and a fixed amount of gas in it and put it out in the sun, its volume will increase over time. As the temperature increases, its volume also increases. As children, we would put a ball out in the sun and then we would play. (Observation, April 04, 2013)

When asked the reason for using daily life examples, Mehmet stated:

Mehmet: I used these examples to enable students to understand the applications of the concepts that they learned in the lesson in daily life. (Interview, April 08, 2013)

To sum up, participants generally performed their lessons by giving examples from daily life. However, they did not mention under what conditions the examples they used were valid or invalid. They did not adequately explain the relationships between concepts and daily life examples.

Knowledge of learner

When participants’ KoL were compared for two topics, it was seen that participants had a rich knowledge of students’ pre-requisite knowledge for the topics. They tried to determine their pre-requisite knowledge by using the question-answer technique and made necessary alterations in their lessons based on the students’ pre-requisite knowledge Conversely, they had very little knowledge of students’ difficulties and misconceptions in these topics. The participants’ knowledge of the students’ difficulties in the topics was mostly obtained through their professional experience. Moreover, their KoL differed in terms of student's difficulties and misconceptions for each topic. In the topic of interactions between chemical species, the participants highlighted the abstract nature of the topic to deal with students’ difficulties and misconceptions, while they cited familiar examples to deal with students’ difficulties and misconceptions in the topic of states of matter.

Highlighting abstract nature. For the topic of interactions between chemical species, the participants expressed that the students would have problems throughout the entire topic. They stated that students had difficulties in grasping the idea that a bond has both ionic and covalent characteristics, difficulties in envisioning chemical species, difficulties in understanding the p–p orbital overlap, and confusing molecule polarity and bond polarity. Moreover, they said that the reason for these difficulties was the abstract nature of the topic. The expression Mehmet gave is as follows:

Mehmet: The most difficult part about teaching the topic of interactions between chemical species is the abstract nature of the topic. (Interview, May 20, 2013)

Throughout the topic, the participants made explanations highlighting the abstract nature of the concepts to deal with students’ difficulties on this topic. However, they rarely warned their students about the misconceptions they were aware of, they did not carry out any activities to eliminate these misconceptions in their lessons. They tried to eliminate students’ misconceptions just by emphasizing abstract nature. For example, in one of her lessons on this topic, Zeynep warned her students about the misconception that protons are exchanged in chemical events. Zeynep expressed her opinions about the reason for this misconception as follows:

Zeynep: Students who do not fully comprehend the atom models are unable to understand chemical events and bond formation. Some students think that protons play a role in bond formation. I underlined the fact that the particle that is exchanged is the electron. (Interview, January 10, 2013)

Highlighting familiar examples. For the topic of states of matter, the participants used examples familiar to students to prevent students from experiencing difficulty or having misconceptions. While explaining the concepts on this topic, they always gave daily life examples that were familiar to the students. The participants verbally warned their students about the difficulties and tried to prevent these difficulties by highlighting familiar examples. For example, they explained the surface tension with the example of insects walking on the water because they thought that students might have difficulty in understanding this concept. They warned their students about the misconceptions that evaporation does not happen without boiling, and that evaporation and boiling are the same things, and they tried to remove these misconceptions using the experiences of students about evaporation and boiling in daily life. In addition, Zeynep conducted one activity for a misconception she noticed thanks to her professional experience. In this activity, she brought a Celsius thermometer to the classroom and had all her students examine the thermometer. When asked in the interview after the lesson why she carried out this activity, she answered:

Zeynep: Students think of the Celsius thermometer as a pipe of 100 cm. It was from previous years that I noticed this about my students. I was so surprised about that; I never expected such a thought from my students. To prevent this misconception, I brought a thermometer to the classroom. (Interview, April 04, 2013)

In summation, in both topics, the participants obtained their KoL from their professional experience, did not have enough level of knowledge about student difficulties and misconceptions in these topics, and did not follow studies that have been conducted in this field. To prevent difficulties and misconceptions, they highlighted abstract nature in the topic of interactions between chemical species and familiar examples in the topic of states of matter.

Knowledge of assessment

When examining the participants’ KoA, it was seen that their KoA consisted of general pedagogical knowledge. The participants’ KoA in the topics did not differ according to the topic.

How to assess and purpose of the assessment. The participants evaluated the students’ prior knowledge about the topics by asking a few questions. The questions that were asked to reveal prior knowledge were generally at a low cognitive level and were asked to refresh the students’ memory about the topics, such as “How does an ionic bond form?” and “What are the differences between liquids and gases?”. When assessing the students’ prior knowledge, participants did not assess the entire class; rather, they only established the prior knowledge of the few students who answered their questions. Similarly, in terms of formative assessment, the participants only assessed a few students’ understanding during the teaching process. They used the question-answer technique as a formative assessment method for both topics. In addition to this, they tried to understand, informally, whether the students understood by looking at the students’ faces. Examples of the questions asked by the participants during the teaching process are given below:

Zeynep: What is the definition of chemical species? (Observation, January 07, 2013)

Mehmet: In a volume-stable container, there is H₂ gas containing 6.02 × 10²³ atoms, 2.8 g of N₂ gas, and 6.4 g of CH₄ gas. If the total pressure is 300 mmHg, then, what is the total pressure of the N₂ gas? (Observation, April 05, 2013)

At the end of the topics, the participants carried out a summative assessment for the entire class using traditional assessment methods. They judged the students’ understanding based on written test results. When the exam questions they applied were investigated, it was found that the questions were formed in such a way as not to prompt high-level thinking of the students but rather to elicit the exact responses memorized from the questions posed in the lessons. For both topics, the questions in the exams were like the questions used in the lessons and problems requiring mathematical operations. In the exams, they used true/false, matching, multiple-choice, open-ended and fill-in-the-blank questions. Examples of exam questions used by the participants are given below:

Exam question (Mehmet): Some chemical species are given below. Please indicate the interactions among these chemical species.

(a) Na⁺/H₂O (b) I₂/CCl₄ (c) H₂O/CH₃COOH

Exam question (Zeynep): How many kJ of heat should be given to increase the temperature of 125 g of pure water from 20 °C to 80 °C? (c_water = 4.18 J g⁻¹ °C⁻¹)

(a) 20.90 (b) 31.35 (c) 41.80 (d) 62.70 (e) 94.05

What to assess. The participants generally only assessed the science content of interactions between chemical species and the science content of states of matter. They often did not consider points like scientific process skills, nature of scientific understanding, daily life relations, or interdisciplinary relations when carrying out assessment in either of the topics. However, they did assess scientific process skills albeit at a very basic level for the topic of states of matter. For example, while teaching ideal gas law, the participants assessed the students’ skills in drawing and interpreting graphs. In assessing the students’ understanding, they generally used questions at a low cognitive level, which served only to determine whether the students remembered, not their conceptual understanding.

In terms of KoA, exams were the basic tools that the participants used to perform summative assessments. Here, the focus was on the students’ ability to make mathematical operations. In addition, the participants did not go beyond the traditional assessment methods in the exams. In summary, the participants’ KoA in the topics of interactions between chemical species and states of matter were not topic-specific.

Conclusions and discussion

This study aimed to investigate the topic-specific nature of two experienced chemistry teachers’ PCK in the topics of interactions between chemical species and states of matter. PCK is identified in the literature as a topic-specific knowledge type (Abell, 2008; Magnusson et al., 1999; Mthethwa-Kunene, 2014; Veal and MaKinster, 1999). In this study, it was found that both teachers’ PCKs were specific on the interactions between chemical species and states of matter. However, the topic-specific nature was not observed in terms of certain sub-dimensions of PCK. This suggests that despite their professional experiences, the chemistry teachers were not sufficiently knowledgeable on how to shape their teaching in such a way as to be specific to a topic. PCK is not only topic-specific but also context-and person-specific and the development of PCK is influenced by professional experience (Aydin, 2012; Cooper et al., 2015; Friedrichsen, 2002; Friedrichsen and Dana, 2003; Park and Suh, 2015; Sande, 2010). It is probable that throughout the chemistry teachers’ professional careers, the components of their PCK might not have developed equally and their PCKs were influenced by the university entrance exam, anxiety to complete the curriculum on time, and parent pressure.

It was found that the chemistry teachers’ OSTs were similar and exam-focused for both topics. The current nature of the educational system, which places great emphasis on preparing students for the university entrance exam, was reflected in their OSTs (Nargund-Joshi et al., 2011). According to Aydin et al. (2014); Friedrichsen et al. (2009) OSTs are not topic-specific. We found that Mehmet's OSTs were teacher-centered for both topics, but Zeynep's OST for the topic of interactions between chemical species was between student-and teacher-centered and her OST for the topic of states of matter was teacher-centered. Since Zeynep was more experienced than Mehmet in terms of determining students’ prior knowledge and being aware of former students’ misconceptions, she had a more student-centered OST. It implies that teaching experience influences a science teacher's OST (Akın and Uzuntiryaki-Kondakci, 2018) and a teacher with a student-centered OST has greater in-depth student knowledge (Walter, 2013). However, Zeynep had didactic OST for the topic of states of matter. Since she had more concepts to teach on this topic, she was anxious to complete the curriculum on time and returned to teacher-centered teaching. Time constraint was one of the main contextual factors that influenced Zeynep's OST. It seems that teachers prefer teacher-centered teaching when they have more concepts to teach to save time (Aydin, 2012; Friedrichsen and Dana, 2005; Samuelowicz and Bain, 1992).

Both teachers’ KoC were similar in terms of knowledge about the objectives, the special warnings in the curriculum, and vertical and horizontal relations in the curriculum. The topics of interactions between chemical species and states of matter are interrelated and placed consecutively in the chemistry curriculum. In addition, the horizontal and vertical relations in these topics that can be established with other chemistry topics are similar. It is likely that KoC of the teachers might not be topic-specific in some respects because of the relations among the topics. However, the teachers’ KoC differed in terms of relations with other disciplines and curriculum sequence across the topics. While they followed the curriculum sequence for the topic of interactions between chemical species, they altered the curriculum sequence to make positive changes in students’ understanding of the topic of states of matter. According to Ekiz-Kiran and Boz (2020); Lee and Luft (2008), experienced teachers reorganize the curriculum to affect their students’ learning in a positive way and make their instruction relevant to their students.

Neither teacher used science-specific strategies in their lessons for either topic. According to Ekiz-Kiran and Boz (2020); Park and Chen (2012), the teaching strategies that teachers use are affected by their OSTs. It seems that as a result of their teacher-centered OSTs, the teachers presented the content through lecturing without doing the experiments suggested by the curriculum for either topic. Conversely, both teachers’ topic-specific strategies were found to be specific on interactions between chemical species and states of matter. While the chemistry teachers focused on abstract nature and used analogies, role-playing, and ball-stick models in the topic of interactions between chemical species, they focused on daily life examples in the topic of states of matter. Although there are concepts that they can explain in the topic of states of matter through abstract nature; they preferred daily life examples that students are familiar with to facilitate student learning. This seems to be in line with the principle of learning from concrete to abstract. However, the microscopic level, which is one of the most important levels in students’ learning in chemistry, was therefore missed by the teachers. Analogies, role-playing, and ball-stick models are the methods that can be used to embody the abstract concepts, such as the concepts in the topic of interactions between chemical species, and make these concepts understandable for students (Braund, 2015; Coll et al., 2005; Dagher, 1998; Maharaj-Sharma, 2008; Treagust and Harrison, 2000). However, in this study, the implementation of topic-specific strategies by the chemistry teachers had some deficiencies and was not sufficiently effective. It seems that the teachers use analogies without planning for them and create them extemporarily (Dagher, 1995; Thiele and Treagust, 1994) and prefer daily life examples to connect science and students’ life (Sande, 2010; Şen, 2014).

In terms of KoL, the teachers were found to be knowledgeable in both topics in terms of students’ pre-requisite knowledge. However, their knowledge of students’ difficulties and misconceptions, was limited in both topics. To overcome these difficulties and misconceptions, they highlighted the abstract nature in the topic of interactions between chemical species and familiar examples in the topic of states of matter. When the results obtained for KoIS and KoL are considered together, it can be said that when there are examples of students familiar with the topic, the teachers focus on these examples during their teaching. According to Walter (2013), teachers, thanks to their professional experience, can gain expertise in determining points where students have difficulties. This suggests that, despite their professional experience, KoL of the chemistry teachers might not have been developed enough in the present study.

Both teachers’ KoAs were found to be general pedagogical knowledge in both the interactions between chemical species and states of matter. While their teaching on these topics differed from each other, neither teacher's KoA was topic-specific. They only assessed the science content of the topics and often solved questions requiring mathematical operations just like in the university entrance exam. Moreover, they did not use alternative assessment methods suggested by the curriculum for either topic. The preferences for their assessment approaches can likely be attributed to their exam-focused OSTs. In other words, it can be concluded that the traditional and exam-focused lenses through which the chemistry teachers viewed teaching prompted them to carry out similar assessment approaches. Magnusson et al.'s PCK model (1999) considered KoA as topic-specific however our findings are similar to previous studies conducted by Aydin et al. (2014); Hanuscin et al. (2011) that challenge the situation of KoA on Magnusson et al.'s (1999) model. It seems that KoA needs more time to develop rather than the other PCK components (Hanuscin et al., 2011; Henze et al., 2008). On the other hand, PCK for assessment may not be topic-specific, and targeted professional development may be required for topic-specific KoA (Aydin et al., 2014).

Implications

This study investigated the topic-specific nature of only two experienced chemistry teachers’ PCK in the topics of interactions between chemical species and states of matter. Therefore, the results of this study cannot be generalized to different teachers, topics, and contexts. Nevertheless, due to the impact of PCK on teachers’ professional knowledge and its role in teacher training, the results of this study have implications for in-service chemistry teacher education, pre-service chemistry teacher education, and chemistry education researchers.

This study underlined the need to train teachers in developing their topic-specific PCK and in constructing their topic-specific teaching to help them improve their topic-specific PCK. It is recommended that in-service training be provided to present instructional strategies for teaching a chemistry topic and, to show teachers how to benefit from the curriculum governing this topic, how to assess learners’ pre-requisite knowledge of the topic, and how to remove the misconceptions stated in the literature about the topic. In this way, chemistry teachers’ PCK can become more topic-specific. Furthermore, even though teachers’ professional knowledge specific to a topic has been developed, teachers may not be able to use this knowledge effectively in a classroom application due to the many filters that a teacher's topic-specific PCK must pass through, such as their beliefs and OST, context, and personal abilities. Therefore, in addition to the in-service training targeted at improving their topic-specific PCK, further investigation into how teachers apply this knowledge in their classrooms and the factors causing any deficiencies in practice is recommended.

This study showed that chemistry teachers obtained their knowledge in some components of PCK through their professional experience. As stated in the literature, experienced teachers have more robust PCK than pre-service teachers. However, chemistry teacher educators should focus on how the content can be taught in a topic-specific way, as well as the content itself, to develop pre-service chemistry teachers’ topic-specific PCK.

The topics of interactions between chemical species and states of matter were 10th-grade chemistry topics when this study was conducted. Grade level is one of the elements that can influence a teacher's PCK. For this reason, further studies should analyse chemistry teachers’ PCK in contexts where the topics of interactions between chemical species and states of matter are taught under the chemistry curriculum at different grade levels and investigate whether teachers’ PCK in these topics differ according to grade level.

In this study, some components of PCK or some sub-dimensions of components were not found to be topic-specific for the topics of interactions between chemical species and states of matter. The reasons for this may be that these two topics are interrelated and successive. Therefore, it is recommended that chemistry education researchers examine the topic-specific nature of PCK for interrelated (e.g. reaction rate and chemical equilibrium) and unrelated (e.g. modern atomic theory and thermochemistry) topics in future studies. In this way, the differences and similarities that may arise from interrelated and unrelated topics could contribute to the understanding of the topic-specific nature of PCK.

Conflicts of interest

There are no conflicts to declare.

Appendix

Sample scenarios in card-sorting activities prepared for both topics

• An effective way to teach students about the factors affecting evaporation rate is to create suitable learning environments in which students can develop their science process skills. (Process)

• One way to teach bond energies effectively is to solve difficult and challenging questions for students. (Academic rigor)

• A good way to teach students about the kinetic theory of gases is to present information through lecturing and to ask questions to see if students know scientific facts. (Didactic)

• One way to teach real gases effectively is to do an activity and/or to ask a question that will check the prior knowledge of the students, and try to eliminate their misconceptions by using an analogy and/or doing an experiment etc. (Conceptual change)

• One way to teach the effect of hydrogen bonding on boiling point effectively is to have students do hands-on activities based on verification or exploration. (Activity-driven)

• One way to teach the effect of temperature on viscosity effectively is to plan an investigation for students that allows them to discover the viscosities of different substances at different temperatures. (Discovery)

• An effective way to teach Graham's diffusion law is to have students prepare a project on how diffusion is used to enrich the uranium-235 (²³⁵U) isotope. (Project-based science)

• A good way to teach the relationship between pressure and volume in gases is to allow students to explore and describe the problem related to the topic, conduct research, design their experiments, make inferences, and evaluate the validity of knowledge from their own conclusions. (Inquiry)

• An effective way to teach the relationship between bond energy and bond strength, under the guidance of the teacher, is to have students design their own experiments for solving the problem posed by the teacher, obtain their data, assess the validity of their data, and make inferences according to their results. (Guided inquiry)

The interview questions about the card-sorting activity

• You thought that these scenarios represent your teaching well. Why do they reflect your teaching? Could you please explain the similarities between these scenarios in this group? What are the common properties of these scenarios? (the scenarios that best represent her/his teaching)

• You thought that these scenarios do not represent your teaching. Why do not they reflect your teaching? Could you please explain the similarities between these scenarios in this group? What are the common properties of these scenarios? (the scenarios that do not represent her/his teaching)

• You stated that you are not sure whether these scenarios reflect your teaching or not. Why are you unsure about them? Could you please explain the similarities between these scenarios in this group? What are the common properties of these scenarios? (the scenarios that she/he is unsure)

Sample points in the semi-structured observation form used in the observations made during the lessons

OST:

• The teacher explains why the topic should be learned.

• The teacher explains how the topic can be learned better.

KoC:

• The teacher makes connections with other chemistry topics/other disciplines in the topic.

• The teacher changes the curriculum sequence based on something that occurs in the classroom.

KoIS:

• The teacher uses an analogy/role-playing/an example/a molecule model/a daily life example, etc. to explain a concept.

• The teacher makes an instructional decision that changes the flow of the lesson.

KoL:

• The teacher does or does not recognize potential difficulties or misconceptions of students.

• The teacher does or does not do something to overcome students’ difficulties or misconceptions.

KoA:

• The teacher does or not does use traditional or/and alternative assessment methods.

• The teacher does or does not assess the understanding/prior knowledge/scientific process skills/nature of science etc. of the students.

Sample questions in weekly semi-structured interviews done after the lesson

• What were your purposes for this week's lesson? How do you plan your lesson according to these purposes? (for OST/KoC)

• Which sources did you use while planning the lesson? (for KoC)

• Did you carry out your lesson as planned? Did you stray from your plan? If you strayed from your plan, can you explain why? (for KoC/KoIS)

• How did the curriculum guide you while you were teaching? Did you change anything from the curriculum? If you did, could you please explain why you made this change? (for KoC)

• Can you tell me something about the analogy/role-playing/example/molecule model/daily life example etc. you use? Why did you use that? How did this analogy/role-playing/example/molecule model/daily life example etc. help students’ understandings about this topic? (for KoIS)

• Do you think students had difficulties at any point? Why do you think they had difficulties at that point? How did you overcome these difficulties for students? Have you detected any misconceptions in your students? How did you notice this misconception? What did you do to correct the student's misconception? (for KoL)

• What do you think the students learned as a result of this lesson? How did you find out that the students learned them? (for KoA)

Sample questions in final semi-structured interviews done to compare the teachings in both topics

• What are the similarities in teaching the topics of interactions between chemical species and states of matter?

• What are the differences in teaching these topics?

• Do you think teaching one of them is more difficult than teaching the other? Why do you think so?

• Which analogy/role-playing/example/molecule model/daily life example, etc. do you use for teaching the topics of interactions between chemical species and states of matter? Can you compare the features of these strategies used for teaching the topics of interactions between chemical species and states of matter?

• Can you tell me about your knowledge about students’ difficulties and misconceptions in the topics of interactions between chemical species and states of matter? How do you overcome these difficulties and misconceptions for both topics?

• How do you assess your students in the topics of interactions between chemical species and states of matter? Which assessment techniques do you use to assess the students for both topics? Can you compare them? What do you assess in your students for both topics?

References

1. Abell S. K., (2007), Research on science teacher knowledge, in Abell S. K. and Lederman N. G. (ed.), Handbook of research on science education, New Jersey: Lawrence Erlbaum Associates, pp. 1105–1149.
2. Abell S. K., (2008), Twenty years later: Does pedagogical content knowledge remain a useful idea? Int. J. Sci. Educ., 30(10), 1405–1416.
3. Akın F. N. and Uzuntiryaki-Kondakci E., (2018), The nature of the interplay among components of pedagogical content knowledge in reaction rate and chemical equilibrium topics of novice and experienced chemistry teachers, Chem. Educ. Res. Pract., 19(1), 80–105.
4. Aydin S., (2012), Examination of chemistry teachers’ topic-specific nature of pedagogical content knowledge in electrochemistry and radioactivity (unpublished doctoral dissertation), Ankara: Middle East Technical University.
5. Aydin S. and Boz Y., (2012), Review of studies related to pedagogical content knowledge in the context of science teacher education: Turkish case, Educ. Sci.: Theory Pract., 12(1), 479–505.
6. Aydın S., Demirdöğen B., Tarkın A., Kutucu S., Ekiz B., Akın F. N., Tuysuz M. and Uzuntiryaki E., (2013), Providing a set of research-based practices to support preservice teachers’ long-term professional development as learners of science teaching, Sci. Educ., 97(6), 903–935.
7. Aydin S., Friedrichsen P. M., Boz Y. and Hanuscin D. L., (2014), Examination of the topic-specific nature of pedagogical content knowledge in teaching electrochemical cells and nuclear reactions, Chem. Educ. Res. Pract., 15(4), 658–674.
8. Ayyıldız Y. and Tarhan L., (2013), Case study applications in chemistry lesson: gases, liquids, and solids, Chem. Educ. Res. Pract., 14, 408–420.
9. Ball D. L. and Bass H., (2000), Interweaving content and pedagogy in teaching and learning to teach: Knowing and using mathematics, in Boaler J. (ed.), Multiple perspectives on the teaching and learning of mathematics, Westport, CT: Ablex, pp. 83–104.
10. Barnett J. and Hodson D., (2001), Pedagogical context knowledge: Toward a fuller understanding of what good science teachers know, Sci. Educ., 85(4), 426–453.
11. Berliner D. C., (2001), Learning about and learning from expert teachers, Int. J. Educ. Res., 35(5), 463–482.
12. Berry A., Loughran J. and van Driel J. H., (2008), Revisiting the Roots of Pedagogical Content Knowledge, Int. J. Sci. Educ., 30(10), 1271–1279.
13. Bransford J., Darling-Hammond L. and LePage P., (2005). Introduction, in Darling-Hammond L. and Bransford J. D. (ed.), Preparing teachers for a changing world: What teachers should learn and be able to do, San Francisco, CA: Jossey-Bass, pp. 1–39.
14. Braund M., (2015), Drama and learning science: An empty space?, Br. Educ. Res. J., 41(1), 102–121.
15. Chen B. and Wei B., (2015), Examining chemistry teachers’ use of curriculum materials: In view of teachers’ pedagogical content knowledge, Chem. Educ. Res. Pract., 16, 260–272.
16. Coll R. K., France B. and Taylor I., (2005), The role of models/and analogies in science education: Implications from research, Int. J. Sci. Educ., 27(2), 183–198.
17. Cooper R., Loughran J. and Berry A., (2015), Science teachers’ PCK: Understanding sophisticated practice, in Berry A., Friedrichsen P. and Loughran J. (ed.), Re-examining pedagogical content knowledge in science education, New York, NY: Routledge, pp. 60–74.
18. Creswell J. W., (1994), Research design: Qualitative & quantitative approaches, Thousand Oaks, CA: Sage.
19. Dagher Z. R., (1995), Analysis of analogies used by science teachers, J. Res. Sci. Teach., 32(3), 259–270.
20. Dagher Z. R., (1998), The case for analogies in teaching science for understanding, in Mintzes J. J., Wandersee J. H. and Novak J. D. (ed.), Teaching science for understanding: A human constructivist view, California: Academic, pp. 195–211.
21. Davis E. A., (2003), Knowledge integration in science teaching: Analysing teachers’ knowledge development, Res. Sci. Educ., 34(1), 21–53.
22. De Jong O. and van Driel J., (2001), The development of prospective teachers’ concerns about teaching chemistry topics at a macro-micro-symbolic interface, in Behrednt H., Dahncke H., Duit R., Graber W., Komorek M., Kross A. and Reiska P. (ed.), Research in science education: Past, present and future, Dordrecht, The Netherlands: Kluwer Academic, pp. 271–276.
23. Ekiz-Kiran B. and Boz Y., (2020), Interactions between the science teaching orientations and components of pedagogical content knowledge of in-service chemistry teachers, Chem. Educ. Res. Pract., 21, 95–112.
24. Evens M., Elen J. and Depaepe F., (2015), Developing pedagogical content knowledge: Lessons learned from intervention studies, Educ. Res. Int., 1–23.
25. Friedrichsen P. J., (2002), A substantive-level theory of highly-regarded secondary biology teachers’ science teaching orientation (unpublished doctoral dissertation), Pennsylvania: The Pennsylvania State University.
26. Friedrichsen P., Abell S. K., Enrique P. M., Brown P. L., Lankford D. M. and Volkmann M. J., (2009), Does teaching experience matter? Examining biology teachers’ prior knowledge for teaching in an alternative certification program, J. Res. Sci. Teach., 46(4), 357–383.
27. Friedrichsen P. M. and Dana T. M., (2003), Using a card-sorting task to elicit and clarify science-teaching orientations. J. Sci. Teach. Educ., 14(4), 291–309.
28. Friedrichsen P. M. and Dana T. M., (2005), Substantive-level theory of highly regarded secondary biology teachers’ science teaching orientations, J. Res. Sci. Teach., 42(2), 218–244.
29. Friedrichsen P., Lankford D., Brown P., Pareja E., Volkmann M. and Abell S., (2007), The PCK of future science teachers in an alternative certification program, Paper presented at the National Association for Research in Science Teaching Annual Conference, New Orleans, LA.
30. Geddis A. N., Onslow B., Beynon, C. and Oesch J., (1993), Transforming content knowledge: Learning to teach about isotopes, Sci. Educ., 77(6), 575–591.
31. Gess-Newsome J., (2015), A model of teacher professional knowledge and skill including PCK: Results of the thinking from the PCK summit, in Berry A., Friedrichsen P. and Loughran J. (ed.), Re-examining pedagogical content knowledge in science education, New York: Routledge, pp. 28–42.
32. Grossman P. L., (1990), The making of a teacher: Teacher knowledge and teacher education, New York: Teachers College.
33. Hanuscin D. L., Lee M. H. and Akerson V. L., (2011), Elementary teachers’ pedagogical content knowledge for teaching the nature of science, Sci. Educ., 95(1), 145–167.
34. Henze I., van Driel J. H. and Verloop N., (2008), Development of experienced science teachers’ pedagogical content knowledge of models of the solar system and the universe, Int. J. Sci. Educ., 30(10), 1321–1342.
35. Lankford D., (2010), Examining the pedagogical content knowledge and practice of experienced secondary biology teachers for teaching diffusion and osmosis (unpublished doctoral dissertation), Columbia: University of Missouri.
36. Lee E., Brown M., Luft J. A. and Roehrig G., (2007), Assessing beginning secondary science teachers’ PCK: Pilot year results, Sch. Sci. Math., 107(2), 418–426.
37. Lee E. and Luft J. A., (2008), Experienced secondary science teachers’ representation of pedagogical content knowledge, Int. J. Sci. Educ., 30(10), 1343–1363.
38. Maharaj-Sharma R., (2008), Using role-play to develop science concepts, Caribbean Curr., 15, 25–43.
39. Magnusson S., Krajcik J. and Borko H., (1999), Nature, sources and development of pedagogical content knowledge for science teaching, in Gess-Newsome J. and Lederman N. G. (ed.), Examining pedagogical content knowledge, Dordrecht, Netherlands: Kluwer Academic Publishers, pp. 95–132.
40. Martin N. K., Yin Z. and Mayall H., (2006), Classroom management training, teaching experience and gender: Do these variables impact teachers’ attitudes and beliefs toward classroom management style?, Paper presented at the Annual Meeting of the Southwest Educational Research Association, Austin, Texas.
41. Mavhunga E., (2016), Transfer of the pedagogical transformation competence across chemistry topics, Chem. Educ. Res. Pract., 17, 1081–1097.
42. Merriam S., (2009), Qualitative research: A guide to design and implementation, San Francisco, CA: Jossey-Bass.
43. Miles M. B. and Huberman A. M., (1994), Qualitative data analysis: An expanded sourcebook, 2nd edn, Thousand Oaks, California: Sage.
44. Mthethwa-Kunene K. E. F., (2014), Exploring science teachers’ pedagogical content knowledge in the teaching of genetics in Swaziland (unpublished doctoral dissertation), Pretoria: University of Pretoria Faculty of Education.
45. Nargund-Joshi V., Park Rogers M. A. and Akerson V. L., (2011), Exploring Indian secondary teachers’ orientations and practice for teaching science in an era of reform, J. Res. Sci. Teach., 48(6), 624–647.
46. Nilsson P. and Elm A., (2017), Capturing and developing early childhood teachers’ science pedagogical content knowledge through CoRes, J. Sci. Teac. Educ., 28(5), 406–424.
47. Okanlawon A. E., (2010), Teaching reaction stoichiometry: Exploring and acknowledging Nigerian chemistry teachers pedagogical content knowledge, Cypriot J. Educ. Sci., 5(2), 107–129.
48. Park S. and Chen Y. C., (2012), Mapping out the integration of the components of pedagogical content knowledge (PCK): Examples from high school biology classrooms, J. Res. Sci. Teach., 49, 922–941.
49. Park S. and Suh J. K., (2015), From portraying toward assessing PCK: Drivers, dilemmas, and directions for future research, in Berry A., Friedrichsen P. and Loughran J. (ed.), Re-examining pedagogical content knowledge in science education, New York, NY: Routledge, pp. 104–119.
50. Patton M. Q., (2002), Qualitative research and evaluation methods, 3rd edn, Thousand Oaks, CA: Sage.
51. Rollnick M., Bennett J., Rhemtula M., Dharsey N. and Ndlovu T., (2008), The place of subject matter knowledge in pedagogical content knowledge: A case study of South African teachers teaching the amount of substance and chemical equilibrium, Int. J. Sci. Educ., 30(10), 1365–1387.
52. Rollnick M. and Mavhunga E., (2014), PCK of teaching electrochemistry in chemistry teachers: A case in Johannesburg, Gauteng Province, South Africa, Educ. Quimica, 25(3), 354–362.
53. Samuelowicz K. and Bain J. D., (1992), Conceptions of teaching held by academic teachers, High. Educ., 24(1), 93–111.
54. Sande M. E. (2010), Pedagogical content knowledge and the gas laws: A multiple case study (unpublished doctoral dissertation), Minnesota: University of Minnesota.
55. Scharfenberg F. J. and Bogner F. X., (2015), A new role change approach in pre-service teacher education for developing pedagogical content knowledge in the context of a student outreach lab, Res. Sci. Educ., 1–24.
56. Schneider R. M. and Plasman K., (2011), Science teacher learning progressions: A review of science teachers’ pedagogical content knowledge development, Rev. Educ. Res., 81(4), 530–565.
57. Shulman L. S., (1986), Those who understand: Knowledge growth in teaching, Educ. Res., 15(2), 4–14, retrieved from http://www.fisica.uniud.it/URDF/masterDidSciUD/materiali/pdf/Shulman_1986.pdf.
58. Shulman S., (2015), PCK: Its genesis and exodus, in Berry A., Friedrichsen P. and Loughran J. (ed.), Re-examining pedagogical content knowledge in science education, New York, NY: Routledge, pp. 3–13.
59. Soysal Y., (2018), An exploration of the interactions among the components of an experienced elementary science teacher's pedagogical content knowledge, Educ. Stud., 44(1), 1–25.
60. Stender A., Brückmann M. and Neumann K., (2017), Transformation of topic-specific professional knowledge into personal pedagogical content knowledge through lesson planning, Int. J. Sci. Educ., 39(12), 1690–1714.
61. Şen M., (2014), A study on science teachers’ pedagogical content knowledge and content knowledge regarding cell division (unpublished master's thesis), Ankara: Middle East Technical University.
62. Thiele R. B. and Treagust D. F., (1994), An interpretive examination of high school chemistry teachers’ analogical explanations, J. Res. Sci. Teach., 31(3), 227–242.
63. Treagust D. F. and Harrison A. G., (2000), In search of explanatory frameworks: An analysis of Richard Feynman's lecture ‘Atoms in motion’, Int. J. Sci. Educ., 22(11), 1157–1170.
64. Tsaparlis G., Pappa E. T. and Byers B., (2018), Teaching and learning chemical bonding: Research-based evidence for misconceptions and conceptual difficulties experienced by students in upper secondary schools and the effect of an enriched text, Chem. Educ. Res. Pract., 19, 1253–1269.
65. Van Driel J. H., Berry A. and Meirink J., (2014), Research on science teacher knowledge, in Lederman N. G. and Abell S. K. (ed.), Handbook of research on science education, New York, NY: Routledge, pp. 848–870.
66. Veal W. R. and MaKinster J. G., (1999), Pedagogical content knowledge taxonomies, Electron. J. Sci. Educ., 3(4), retrieved from http://wolfweb.unr.edu/homepage/crowther/ejse/vealmak.html.
67. Walter E. M., (2013), The influence of pedagogical content knowledge (PCK) for teaching macroevolution on student outcomes in a general education biology course, (unpublished doctoral dissertation), Columbia, Missouri: University of Missouri.
68. Yin R. K., (2003), Case study research: Design and methods, 3rd edn, Thousand Oaks, CA: Sage.

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Footnote

† This study has been developed from the doctoral thesis conducted by the first author under the supervision of second author. We thank The Scientific and Technological Research Council of Turkey (TÜBİTAK) due to the support it provided to the first author of this study throughout her doctoral dissertation.

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