Chemical bonding in Swedish upper secondary school education: a force-based teaching model for enhanced understanding
Catalin
Koro Arvidsson
Sven Erikson's High School, Sven Eriksonsplatsen 1 Borås, Boras 501 80, Sweden. E-mail: catalin.koro.arvidsson@edu.boras.se
First published on 9th November 2024
Abstract
This study investigates if a force-based teaching approach, based on quantum mechanical principles and developed in a lesson study, would enhance the understanding of chemical bonding among upper secondary school students. The teaching approach was based on research on the teaching and learning of chemical bonding. The study included first-year students in upper secondary school in a pretest–intervention–posttest design. During four lessons the students were introduced to the underlying forces leading to the formation of all chemical bonds, specifically focusing on ionic- and covalent bonds. The first lesson, which included a presentation of coulombic interaction as a common basis of bond formation, was developed and improved through a lesson study. The lesson was revised based on feedback from 75 students describing why chemical bondings occur. After the four-lesson series about chemical bonding, a total of 67 of the 75 enrolled students had completed both a pre- and a posttest. The students’ answers to the tests were analyzed based on Bernstein's theory of vertical hierarchical and vertical horizontal discourse. The results of the posttests show that 60% of the students demonstrated solely or predominantly vertical hierarchical knowledge structure. These results indicate that most of the students could understand the force-based approach of chemical bonding by using a general theory, spanning over a wide range of the natural science field, with an abstract and specialized language. Moreover, the students who internalized a hierarchichal knowledge discourse about chemical bonding earned higher final grades in the upper secondary school chemistry when compared to students using a horizontal knowledge discourse, indicating that a force-based approach might facilitate a deeper understanding of other subareas within chemistry. In chemistry education research, the effect of using a force-based approach to teach chemical bonding has not previously been widely tested among upper secondary school students. This study responds to the need to test alternative teaching models to facilitate students’ understanding of chemical bonding.
Introduction
Chemical bonding is a fundamental concept in chemistry education and stands as a cornerstone for comprehending general chemistry (Taber and Coll, 2002; Levy Nahum et al., 2010). Given its abstract and theoretical nature, chemical bonding poses a significant challenge for student comprehension (Rocksén, 2022). Several studies identify the topic as associated with a wide range of alternative concepts, misconceptions, and alternative conceptual frameworks due to simplified teaching models about how chemical bonds are formed (for a review see: Özmen, 2004; Ünal et al., 2006; Hunter et al., 2022). One example is the commonly used conceptual model in teaching, the octet framework, which explains the formation of chemical bonds (Taber, 1998; Bergqvist et al., 2013; Croft and de Berg, 2014). The pedagogic approach described can pose problems as it often encourages the belief that atoms are actively “seeking” to achieve “octets” or “full outer shell” configurations, which is an anthropomorphic view. In some cases, anthropomorphic language can be the first stage in developing an understanding of chemical bonding as part of the abstract nature of the atomic world. However, if the students consider that the atoms’ desire to obtain octets can be a sufficient cause of bond formation, the students have no reason to seek other levels of explanation, which is problematic since this explanation offers no help in discussing other important chemical concepts e.g., bond polarity, hydrogen bonding, or van der Waals forces (Taber and Watts, 1996). Thus, this belief may hinder the learning of chemistry at higher levels, as students may struggle to accept chemical processes that do not result in octets. Therefore, it is important to consider the “octet rule” as a rule of thumb rather than a scientific explanation for the formation of molecular bonds.Chemistry textbooks for upper secondary school students (aged 16–19) introduce various bond models and types, which can be challenging for students to grasp (Hurst, 2002; Bergqvist et al., 2013). These models, like the octet framework mentioned earlier, provide simplified explanations of bonding types that can be easily misunderstood by students (Bergqvist and Chang Rundgren, 2017; Tsaparlis et al., 2018). The bonding types presented in chemistry textbooks are traditionally categorized into three major groups – ionic, covalent, or metallic (Hurst, 2002). Typically, the formation of ionic- and covalent bonds resulting from chemical reactions is dichotomously explained as either electron transfer or electron sharing, respectively. Overemphasis on these categories may mislead students and hinder the learning process, especially since many materials cannot be forced into one of the categories due to their bonds being partly ionic and partly covalent.
Levy Nahum and colleagues (2008), amongst others, problematize these traditional approaches by highlighting that chemical bonds are not fundamentally different, as they share the same underlying principles grounded on quantum mechanical principles. To avoid misconceptions regarding the formation and nature of chemical bonds, these researchers propose a new force-based framework for teaching chemical bonding at high school- and university levels, wherein all chemical bonds are treated on a conceptual uniform footing (Taber and Coll, 2002; Levy Nahum et al., 2008; Stevens et al., 2010). In this approach, chemical bonding occurs due to electrostatic forces, proximity, and energy. As a result of Coulomb's law, charged particles within the atoms interact due to simultaneous attractive and repulsive forces. At a specific interatomic distance, the atoms reach equilibrium, reducing the potential energy of the system and resulting in the formation of chemical bonds (Fig. 1; Hägg, 1963, pp. 96–98). It is no doubt that the concept of charge is central for the understanding of the scientifically conditioned idea of the chemical bond. However, charge is rarely described in chemistry textbooks at the upper secondary school-level, which can result in several misconceptions regarding chemical bonding (Croft and de Berg, 2014). Thus, it is important to include an elaboration of the meaning of charge in a force-based teaching-approach. However, some studies suggest that a force-based approach grounded on quantum mechanical principles might be overly demanding at the high school level (Levy Nahum et al., 2008; Stevens et al., 2010). Based on existing research, only one study has investigated the impact of a force-based representation of chemical bonding among lower secondary school students (Joki et al., 2015), one among upper secondary school students (Zohar and Levy, 2019), and one among university students (Venkataraman, 2017). However, these studies include relatively few participating students (38, 21, and 18, respectively). Thus, there is a need to develop and test pedagogic strategies to determine if a force-based framework for teaching chemical bonding is suitable for upper secondary school students.
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| Fig. 1 A schematic energy diagram for two atoms that interact due to attractive and repulsive forces. The figure was inspired by Hägg (1963). | ||
When implementing a new teaching approach, it is important to provide the teachers with three basic supports: (1) high-quality instructional resources, such as teacher manuals or published research about teaching and learning of the specific topic; (2) practice-based opportunities to try out new teaching approaches, and (3) collegial learning that enables the development of shared knowledge, and improvement of lessons (Lewis et al., 2012). These supports become available to teachers when conducting a lesson study, which has been suggested as an effective method to enhance student learning (Ming Cheung and Yee Wong, 2014; Wang et al., 2022), being valuable for developing teachers' knowledge (Lewis et al., 2009) and fostering students' higher-order thinking in science education (Jansen et al., 2021). A lesson study is an iterative research method in which a team of teachers collaborate to improve an actual classroom lesson designed to investigate and improve the teaching of a particular topic. During the research lesson, the lesson study team gathers data on student thinking and learning to visualize what aspects of the lesson design enhance or hinder student learning. The research lesson is improved by the lesson study team and re-evaluated in a post-lesson meeting (Lewis et al., 2012). A graphic illustration of the lesson study cycle has been designed and described by Lewis and colleagues (2006) and has been used as a guideline in the present study (Fig. 2).
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| Fig. 2 Stages in the lesson study cycle as described by Lewis et al. (2006). | ||
Theoretical framework
In this study, Bernstein's concept of the pedagogic discourse is used as a conceptual framework for the analysis Bernstein (1999, 2000). The pedagogic discourse describes the pedagogic communication in classrooms, i.e., what is taught and in what ways (by the teacher) and how it is acquired (by the students).According to Bernstein (2000), the pedagogic discourse is the embedding of two discourses: a regulatory, moral discourse that creates order, relationships, and identities (the how), and an instructional discourse focusing on teaching content, which creates specialized knowledge skills (the what). The instructional discourse is further divided into a horizontal discourse or a vertical discourse based on what knowledge structure it represents. The horizontal discourse could be considered as practical everyday knowledge, or common sense, as it is segmentally organized and context dependent. The vertical discourse is, on the other hand, coherent, explicit, and hierarchically organized. One example of vertical discourse is knowledge structures in scientific or theoretical knowledge, which can be seen as more abstract. Thus, knowledge taught in a school context can be seen as vertically organized. Bernstein describes further that the vertical discourse can be divided into a horizontal and a hierarchical part (Bernstein, 1999). If a vertical hierarchical discourse is used, the teaching includes general theories with a more specialized language, typical for a certain subject. This can be applied to chemical bonding education when a common quantum physical phenomenon is taught, which describes the formation of chemical bonds that can be applied to all atoms (regardless of character) because of electrostatic forces, which results in lower potential energy (described above). This type of education contains more subject-specific concepts and is based on abstract and general theories. To fully understand this, it is important that the teaching includes physical and quantum mechanical concepts, such as energy and how charged particles attract or repel each other according to Coulomb's law. Additionally, students need to understand the structural composition of atoms and the physical properties of their constituents regarding chemical charge. Conversely, in a vertical horizontal discourse setting, elements of a horizontal discourse are recontextualized within the teaching practice, usually to make the teaching more accessible to the students. For instance, different segments of knowledge may be presented independently (i.e., not hierarchically structured). This approach can be applied to the teaching of chemical bonding by divergently introducing various chemical bonds, such as ionic and covalent bonds, dichotomously through electron transfer or sharing mechanisms, respectively. This may be manifested by a teaching model in which basic theories and concepts for a certain phenomenon are avoided. Instead, everyday language and anthropomorphic descriptions of bonding formation may be used.
It is, however, relevant to question whether a vertical hierarchical discourse contributes to better learning, in terms of a higher level of scientific development. Research by Morais (2002) reveals that when there is a weak classification between various scientific contents to be learned (i.e., where the boundaries between content to be learned are blurred as opposed to emphasized), children achieve higher levels of abstraction and, therefore, a more meaningful science education. In addition, the students are given more time to learn because of the repetition of previously learned concepts. Moreover, according to Young (2009), as cited in McLean et al. (2013), students must understand the vertical hierarchal knowledge of their discipline since it will give them access to a more abstract and, thus, more “powerful” knowledge (McLean et al., 2013, p. 267). A more powerful knowledge through a vertical hierarchical discourse will not only give rise to a higher level of critical thinking. It will also give students tools to analyze the world and “voice themselves” by using all discourses available to them (Bourne, 2003). Therefore, learning a vertical hierarchical discourse in chemistry education will give the students broad and powerful knowledge in chemistry and within a large part of the natural science field. This will probably facilitate future studies in chemistry at higher levels and result in a deeper understanding of science.
In this study, a vertical hierarchical discourse is shortly called hierarchical discourse and a vertical horizontal discourse is shortly called horizontal discourse.
Research aims and questions
The present study aims to investigate if teaching a force-based framework as an explanatory model of chemical bonding, developed in a lesson study, is suitable for 16–17-year-old students at the upper secondary school level with no previous knowledge about quantum mechanics. Furthermore, the study aims to investigate if a force-based teaching approach will generate a deeper (hierarchical) knowledge structure of chemical bonding based on scientific explanations of why chemical bonding occurs. These aims are divided into the sub-questions:1. To what extent does a lesson, improved by a lesson study, develop a vertical hierarchical knowledge discourse about ionic bonds, and nonpolar- and polar covalent bonds among upper secondary school students?
2. Will a higher degree of a vertical hierarchical knowledge discourse about chemical bonding correlate with higher final grades in upper secondary school chemistry?
Methods
This study conducted a lesson study to develop a force-based approach for teaching chemical bonding, similar to the approach described by Levy Nahum et al. (2008). The study investigates whether 16–17-year-old students can understand a force-based approach when learning about chemical bonding and if this approach fosters a hierarchical knowledge discourse about chemical bonding among the students. Before the teaching of chemical bonding, students were asked to complete a pretest in class that included eight questions. The pretest was used to assess students’ prior understanding of the nature of chemical bonds. When the teaching of the four-lesson series about chemical bonding ended, the students completed a posttest, which was aimed at analyzing students’ progression about the subject and if the discourse, when the students described chemical bonding, had changed after the educational experience. The pre- and posttest results were analyzed to answer the research questions. The following sections will describe the context of the study, the lesson study and the pre- and posttest in detail.Context of the study
In the Swedish school system, the teaching of chemistry begins at the lower secondary grade (grades 7–9). The Swedish lower secondary chemistry curriculum describes the topics briefly and at a general level. For instance, the teaching of chemical bonds is not directly expressed. However, teachers are obliged to teach about “elements, molecular and ionic compounds and substances transformed through chemical actions”, which indicates that at least covalent and ionic bonds should be mentioned. On the other hand, the curriculum doesn’t state for how long or to what degree this topic should be treated, which means that the students participating in this study may have received differing levels of understanding of chemical bonding before entering upper secondary school. The curriculum for the upper secondary school chemistry first year, which builds on knowledge from compulsory school, states that teaching should cover “models and theories for the structure and classification of matter” and “chemical bonding and its impact on, for instance, occurrence, properties and areas of use for organic and inorganic substances”. In Sweden, this is traditionally taught by the octet framework. Textbooks also present different bonding types, such as covalent and ionic bonds, separately and/or dichotomously. A holistic approach to the common foundation of the chemical bonding is, moreover, missing and the term electrostatic force is rarely used in Swedish chemistry textbooks (Bergqvist et al., 2013).The study participants, drawn from three intact school classes (designated as groups A, B, and C), represents a diverse range of abilities. While the total number of students in these classes were 80, five students did not provide informed consent and were consequently excluded from the study. Therefore, the final sample size consisted of 75 participating students enrolled in the lesson study focusing on the first lesson in the four-lesson series. However, eight of the 75 students did not complete both the pre- and posttest, and were excluded from the part of the study investigating the extent to which students can internalize a hierarchical knowledge discourse about chemical bonding at the end of the four-lesson series and if the degree of hierarchical knowledge about chemical bonding correlate with higher final grades in upper secondary school chemistry. The majority of the students were registered in the city where the school is situated, in the western part of Sweden. The city encompasses ten lower secondary schools. Additionally, some participants were registered in neighboring municipalities, suggesting the participating students are drawn from a relatively extensive area within western Sweden.
Planning and designing of the lessons about chemical bonding
Four chemistry teachers operating at the same school and one researcher (the first author) were enrolled in the lesson study team. The events of the lesson study are outlined in Table 1. Initially, the researcher introduced the chemistry teachers in the lesson study team to the concept of lesson study as a research methodology. Additionally, the researcher presented research findings on learning challenges associated with chemical bonding. Subsequently, team members were invited to share their experiences regarding common student misconceptions about chemical bonding and discuss strategies to address these misconceptions based on the presented research. The team discussed how the Swedish curriculum's learning goals for chemical bonding are typically addressed in chemistry textbooks and how these concepts are introduced in classroom settings. The force-based approach, as described by Levy Nahum et al., (2008), was then introduced to the chemistry teachers (stage 1, Table 1). During a subsequent meeting (stage 2, Table 1), the lesson study team evaluated how this force-based approach aligns with the learning goals in the Swedish curriculum and considered ways it might be efficiently implemented in the lessons on chemical bonding. Thereafter, four lessons about chemical bonding were planned by the researcher and presented to the chemistry teachers in the lesson study team (stages 3–5 in Table 1). The content was designed to cover four 90-minute lessons. The lessons were planned to be carried out consecutively according to the chemistry teachers’ work schedule. As a result, the time between lessons ranged from one to three working days. Subsequently, the chemistry teachers and the researcher discussed and revised the lessons, generating a design model. The four lessons that made up the design model were performed by two of the chemistry teachers in three first-year upper secondary school classes (one teacher in student group A with 27 students and one teacher in student groups B and C, which both consisted of 24 students (stages 7–11 in Table 1)). An overview describing the final versions of the four lessons in the design model is presented in Table 2. The lesson content and order of the lessons are inspired by the force-based framework for teaching chemical bonding first described by Levy Nahum et al., (2008). Approaches to specifically teach the quantum mechanical content in relation to chemical bonding are summarized in Table 3. The summary is intended to assist teachers who use a force-based approach when teaching chemical bonding.| Events in the lesson study | |
| 1 | Seminar for the chemistry teachers in the lesson study team on lesson study |
| The lesson study team discusses common student misconceptions about chemical bonding based on its own experiences and previous research | |
| The lesson study team discusses learning goals concerning chemical bonding according to the Swedish curriculum and how they usually are implemented in chemistry textbooks for upper secondary school students | |
| 2 | The lesson study team discusses how a force-based approach to teaching chemical bonding aligns with the learning goals in the Swedish curriculum |
| The lesson study team discusses learning goals for teaching chemical bonding using a force-based approach | |
| 3 | The lesson study team discusses and revises the content of Lesson 1 |
| 4 | The lesson study team discusses and revises the content of Lesson 2 |
| 5 | The lesson study team discusses and revises the content of Lesson 3 and 4 |
| 6 | The lesson study team discusses and revises the pre- and posttest |
| 7 | The chemistry teachers in the lesson study team conduct the pre-test with students in school |
| 8 | A chemistry teacher in the lesson study team teaches Lesson 1. The rest of the team observes the lesson. The lesson ends by letting the students answer the question: “Why do atoms form chemical bonds” |
| 9 | The lesson study team analyzes and improves Lesson 1 based on classroom observations and the students’ answers to the question described in stage 8 above |
| 10 | The lesson study team repeats the cycle twice with new classes (stages 8–9) |
| 11 | The chemistry teachers in the lesson study team teach Lessons 2, 3, and 4 on different occasions. The researcher observes the lessons. |
| 12 | The chemistry teachers in the lesson study team conduct the posttest with students at the school |
| Lesson | Topics by the curriculum | Teaching content | Detailed description of the teaching design |
|---|---|---|---|
| 1 | Chemical bonding. | Coulombic interaction as a common basis of bond formation. | The lecture included text, digital animations, and short videos demonstrating how oppositely and equally charged objects attracted or repelled each other, respectively. The lecture also included graphs showing enthalpy changes when molecules are formed. |
| Models and theories for the structure and classification of matter. | When chemical bonds are formed, atoms reach a lower energy level, which is the driving force in the formation of all chemical bonds. | A digital simulation was used to show graphs of the potential energy caused by the interatomic distance between two atoms (Physics Education Technology (PhET) Interactive Simulations, 2024). | |
| The Bohr-model and the quantum mechanical model of the atom. | The students answered written exercises linked to the current lesson. The lesson ended by letting the students write an explanation of why two atoms bind to each other by using their own words. | ||
| 2 | The influence of chemical bonds on the occurrence of substances | Ionic bonds form because of the attraction between oppositely charged ions. These bonds are created by electrostatic attractive and repelling forces. | The lecture included text and graphs showing enthalpy changes when ionic compounds are formed, 2D- and 3D models of ionic compounds, and pictures of salt crystals. The teachers also presented 3D models made of balls and sticks and salt crystals created in the lab. |
| When ionic bonds are formed, ionic compounds reach lower potential energy. | The Bohr model of the atomic structure was used to explain how atoms can reach a lower energy level by forming octets. | ||
| The octet framework is a rule of thumb. | The students answered written exercises linked to the current lesson. | ||
| 3 | The influence of chemical bonds on the occurrence of substances | Covalent bond formation, including single, double, and triple bonds. | The lecture included text and graphs showing enthalpy changes when molecules are formed. |
| Models and theories for the structure and classification of matter. | The differences and similarities between ionic bonds and covalent bonds. | The Bohr model of the atomic structure was used to explain how atoms can reach lower potential energy by forming octets. This was done by repeating how electrostatic forces resulted in lower potential energy and bond formation. | |
| The difference between the Bohr model and the quantum mechanical model of the atom. | The students were shown two models of the H2 molecule: the Bohr model and the quantum mechanical model. The students discussed the pros and cons of the models in pairs and subsequently with the teacher. | ||
| The octet framework is a rule of thumb. | The students answered written exercises linked to the current lesson. | ||
| 4 | The influence of chemical bonds on the occurrence of substances | The formation of polar covalent bonds. | The lecture included an explanation of Pauling's scale of electronegativity. |
| Electronegativity. | Digital models of nonpolar molecules, polar molecules, and ionic compounds were illustrated by using the Bohr model and the quantum mechanical model. | ||
| Nonpolar covalent bonds, polar covalent bonds, and ionic bonds can be understood on a continuum scale. | The students answered written exercises linked to the current lesson. | ||
| Aspects of quantum mechanics | Approaches to teaching the quantum mechanical content | Significance for teacher |
|---|---|---|
| The action of charged particles within the atomic system | Force was introduced to the students as the change in velocity of objects in a specific direction. In contrast, electrostatic force was explained by the interaction between charged objects or particles. Specifically, electrostatic force was introduced to the students at a macroscopic level by visualizing how oppositely charged objects attracted each other and how equally charged objects repelled each other. The concept was thereafter used to explain the behaviour of electrons and protons during bond formation (i.e. attraction and repulsion as interatomic forces). | Even if electrostatic force is based on the theory of Coulombs’ law, this theory was not described in detail. Instead, the action of charged particles was established by experiment at a macroscopic level, as described previously. |
| The quantum mechanical model | The wave-particle duality of electrons was reintroduced to the students before showing a quantum mechanical model of hydrogen gas. The visualization of orbitals was explained as the probability of finding an electron at a specific region around the nucleus. | The theory of wave-particle duality of electrons is associated with Heisenberg's indeterminacy principle. However, neither the wave-particle theory nor Heisenberg's indeterminacy principle was explained in detail, since it was considered too demanding for the students to understand. |
| The students compared the Bohr model and the quantum mechanical model of hydrogen gas and highlighted the pros and cons of the different models. | The lectures were limited to only showing the 1s-orbital in hydrogen gas since the goal was to understand the nature of chemical bonding and not to learn the shapes of the different orbitals. | |
| How energy is manifested at an atomic and subatomic level | The emergence of chemical bonds was described as leading to decreased potential energy of the atoms. It was important to state that the formation of chemical bonds do not occur due to the octet formation but because of the laws of thermo dynamics, which implies energy minimization of bound atoms. The formation of chemical bonds will subsequently result in a reduction of chemical reactivity, which is often (but not always) connected to the noble gas structure. | Instead of focusing on the octet framework, energy minimization is a more useful explanation of why chemical bonds are formed. Mainly because senior chemistry textbooks tend to focus on the octet as a model rather than a law (Croft and de Berg, 2014) and to prevent students from developing an anthropomorphic view of bond formation. |
| To demonstrate how the potential energy of the atoms is changed during chemical bond formation, a digital simulation was used (Physics Education Technology (PhET) Interactive Simulations, 2024). | ||
The four lessons about chemical bonding
The intention with the first lesson (Lesson 1, Table 2) was to introduce how all chemical bonds are formed by using a general scientific explanation based on quantum mechanical principles. During this lesson, it was important to explain the concepts of energy and force, and their relation before introducing Coulomb's law as a common basis for bond formation. In specific, the concept of electrostatic force was introduced to the students at a macroscopic level by showing how oppositely charged objects attracted each other and how equally charged objects repelled each other. This was visualized by demonstrating how a charged plastic rod attracted small pieces of paper and made an empty aluminum can roll and, furthermore, how charged balloons interacted when approaching each other (Table 3). To comprehend how charged subatomic particles interact during bond formation, students need to be introduced to the quantum mechanical model of the atom. In this model, electrons are viewed as quantum waves that form orbitals. However, some believe that the quantum mechanical model of atoms, despite being the best-known description of atoms and their interactions, may be too complex for upper secondary school students (Taber, 2001), indicating that the Bohr model is more appropriate when describing the atom since it is less complex and is a sufficient tool for solving simple chemical problems. However, several studies have shown that both the Bohr model and the quantum mechanical model can be introduced to students during the same course since teaching the Bohr-model is not an obstacle to learning the quantum mechanical model (Müller and Weisner, 2002; Kalkanis et al., 2003; McKagan et al., 2008). On the contrary, when students are introduced to both models, they might learn more about a particular case by comparing it to other cases rather than studying it alone (Lowenstein et al., 2003). Therefore, the quantum mechanical model, in combination with the Bohr model, was used to teach why atoms form chemical bonds. Students were also asked to compare the models in pairs and discuss the advantages and disadvantages of using the models. In the first lesson, only the quantum mechanical model of hydrogen gas was shown to the students. This model only involves the interaction of electrons in the 1s-orbital, which was considered as sufficient learning content when approaching chemical bonding for the first time (Table 3).As a second step, a lesson about ionic bonds was designed (see the description of Lesson 2 in Table 2). In line with the force-based approach, the teaching focused on the attractive forces between oppositely charged ions that form an ionic bond, rather than representing ionic bonding in terms of electron transfer and electron receiving to obtain noble gas structure. The octet framework was introduced as one way for the atoms to reach lower energy but was stressed as a role of thumb rather than the reason atoms form chemical bonds. Beginning a series of lessons with ionic bonds before introducing covalent bonds has been suggested by others (Taber and Coll, 2002). However, Lesson 2 was designed to repeatedly refer to Lesson 1 to remind the student that all chemical bonds are formed due to electrostatic attraction- and repulsion between charged subatomic particles to reach lower potential energy.
The intention of Lesson 3 was to introduce single, double, and triple covalent bonds. To avoid presenting ionic and covalent bonds dichotomously, the students were asked to find both differences and similarities between the bond types. Once again, the octet framework was described as a rule of thumb when describing the formation of covalent bonds, and the quantum mechanical model was compared with the Bohr model, as described previously (Lesson 3, Table 2).
Finally, Lesson 4 aimed at describing non-polar covalent bonds, polar covalent bonds, and ionic bonds as a continuum scale, as proposed by Levy Nahum et al. (2008). The lecture included an explanation of Pauling's scale of electronegativity. During this lesson, the quantum mechanical model was used to visualize that the electron cloud is bigger around the most electronegative atom in a polar covalent bond (Lesson 4, Table 2).
Qualitative analysis and revision of Lesson 1
The first lesson intended to explain electrostatic attraction- and repulsion due to Coulomb's law. The students were also introduced to the basic principles of why all chemical bonds are formed due to the driving force of reaching as low interatomic energy as possible. Since the first lesson formed the basis of the entire subject content, the students must understand the content before introducing specific bond types. Hence, the students were asked to write a summary explaining why atoms form chemical bonds at the end of the first lesson (stage 8, Table 1). This task has several benefits. First, retrieval practice is a more effective learning strategy compared to, for example, repeated reading, regardless of individual differences among the learners (Bertilsson, 2023). Second, the students' summaries were used for formal formative assessment, providing insight into the student's understanding of the lesson content. The feedback was directed to the teacher and formed the basis for lesson improvement (Harlen, 2012). Finally, a task directly related to a lesson indicates the learning impact of the lesson content and the interventions made between teaching the student groups. To identify recurrent themes in the students’ summaries, the researcher in the lesson study team conducted an inductive thematic analysis. The data was read from one class at a time, and the themes found in the dataset from one class were presented during a lesson study meeting before the revision of Lesson 1 (stage 9, Table 1). The thematic analysis was made inductively by reading and categorizing the data repeatedly, which made it possible to derive the themes from the data itself, rather than from prior theory or research (Boyatziz, 1998; Braun and Clarke, 2006). The themes were reviewed by the researcher several times to ensure that the themes worked in relation to the quotes from the student answers. Quotes from the data extract were grouped under the thematic headings providing both a description of the theme and visualizing the prevalence of each theme in each class. The frequency of a particular theme offers a sense of extent to which a certain understanding of the lesson content was common among the students, and hence to what degree the quantum mechanical approach was understood by the students.The discussions with the lesson study team during the lesson study meetings and subsequent iterative revisions of the first lesson were based on classroom observations and the thematic analysis of the students’ answers to the question “Why do atoms form chemical bonds?”. To remember the arguments for improvement of Lesson 1, the discussions were audio recorded.
Following the analysis of the first lesson conducted with student group A, the teachers and the researcher decided to improve the lesson by placing more emphasis on the repelling and attractive forces and the particles involved in this process. To achieve this, one of the visuals, which depicted attractive and repelling forces in a hydrogen gas molecule (Fig. 3), was enhanced by adjusting the arrows. The lecture's written content was also slightly modified to highlight how specific atomic particles interact during bond formation. Additionally, the chemistry teachers and the researcher suspected that the students found it challenging to comprehend the schematic diagram representing the potential energy level as a function of the internuclear distance between two atoms (Fig. 1). Consequently, the focus of this diagram was narrowed down to solely describe the strength of the attractive versus the repulsive forces at different internuclear distances and the particles in the atoms involved when the atoms attract and repel each other. It was also decided to perform a “live demonstration” showing how negatively and positively charged objects attract each other, for instance, how a charged plastic rod attracted small pieces of paper. The lesson study team further decided to begin the lesson with a presentation of the learning goals. Finally, the working questions were revised to better align with the lesson.
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| Fig. 3 Two versions of a model representing two hydrogens atoms that form hydrogen gas. (A) shows the model presented to student group A during Lesson 1. (B) shows the revised version of the model, which was used for student group B and C during Lesson 1. | ||
When discussing the lesson taught in student group B, the lecturing teacher described that there was not enough time to let the students work independently at the end of the lesson, mainly because the demonstrations visualizing how negatively and positively charged objects attracted each other was too time-consuming. During the lesson, the teacher showed how a charged plastic rod attracted small pieces of paper with opposite charges and a video clip of how a charged plastic rod made an empty aluminum can roll due to the movement of oppositely charged particles and their attraction to the rod. To save time, the lesson study team revised the lesson by including only one demonstration, which showed the electrostatic attraction between the plastic rod and the paper. Subsequently, student group C got more time to process the lesson content by answering study questions individually and in pairs.
Taken together, the lesson study meetings following Lesson 1 made it possible to pinpoint learning difficulties and clarify key concepts in the lesson content. For example, after teaching student group A the lesson was improved by emphasizing the different forces involved in bond formation and eliminating redundant information when explaining the schematic diagram representing the potential energy level as a function of the internuclear distance between two atoms (Fig. 1). After teaching student group B, the length of the lecture was adjusted, making it possible for the students to process the lesson content.
Design of the pre- and posttest
The intentions with the pre- and posttest were different. The pretest was designed to assess students’ understanding of chemical bonding before the teaching. Students were asked to answer which bonding types they knew from before and how they explained the formation of the bonds by using words and/or by drawing models. The students were also asked if they knew the concept of “electrostatic attraction” from before since this is a key concept in the force-based teaching approach. Moreover, the pretest contained more general questions than the posttest to prevent students from memorizing specific questions that could emerge in the posttest (see appendix). On the other hand, the posttest was designed to assess and evaluate what students had learnt about the lesson content and if the force-based approach, which requires a hierarchical discourse when explaining the formation of chemical bonds, was too demanding for the students (see appendix). The students wrote the posttest approximately one week after ending the last lecture in the study and the students were encouraged to study for the test by their chemistry teachers.Qualitative analysis of the test results
The researcher in the lesson study team analyzed pre- and post-tests using theoretical thematic data analysis (Braun and Clarke, 2006). The theoretical approach in this paper is driven by the interest in finding categories based on Bernstein's theory of vertical horizontal and vertical hierarchical discourse (Bernstein, 1999). Since the data only exists as written test results the categories were identified at a semantic level and no interpretation of the written text was done to look for anything beyond the test answers. To discover the extent to which a vertical hierarchical discourse was used by the students and to identify commonalities among their answers, the tests were analyzed as a whole, rather than analyzing one question at a time. The thematic analysis, inspired by Braun and Clarke (2006), followed several steps. In the first step, the posttests were read several times to identify interesting segments in the raw data and initial ideas of how the data could be organized. The segments of interest were organized into meaningful groups (codes). For instance, the data was coded by categorizing students’ overall description of chemical bonding. In this example, the students’ descriptions were categorized based on whether they described chemical bond formation as the atoms desiring to achieve noble gas structure or by using physical concepts. The codes identified in the raw data were divided into five categories, including (1) how chemical bonding was described in general; (2) if ionic and covalent bonds were described dichotomously or with a similar force-based explanation; (3) how the students explained covalent bond formation; (4) how the student explained ionic bond formation, and; (5) whether the students explained the formation of nonpolar covalent bonds, polar covalent bonds, and ionic bonds as a continuum scale. Finally, subcategories could be identified out of the five categories by showing either a horizontal knowledge structure or a vertical knowledge structure, based on Bernstein's theory of vertical horizontal and vertical hierarchical discourse (Bernstein, 1999). The subcategories were numbered as Horizontal (Ho)1–5 or Hierarchical (Hi)1–5 and are summarized in Table 4. The analysis of the pre- and posttests yielded an analytical tool (Table 4) that was utilized to examine the frequency of each theme for each student, as well as the extent to which students employed horizontal- or hierarchical knowledge discourse when describing chemical bonding. The categories and subcategories are further described in the following sections.| Categories | Horizontal discourse | Hierarchical discourse |
|---|---|---|
| 1. Overall description of chemical bonding | Ho 1 : Anthropomorphic description of chemical bonds | Hi 1 : Quantum mechanical description of chemical bonds |
| The student explains why one or several chemical bonds are formed with anthropomorphic language. Example of student answer: | The student uses one or more physical concepts to describe whether chemical bond is formed because of: | |
| 1. The atoms want to achieve noble gas structure. | 1. Electrostatic attractions, | |
| 2. The atoms want to achieve a lower energy. | 2. or repulsion and/or attraction between particles, | |
| 3. and one of the explanations (1 and/or 2) leads to a lower energy state. | ||
| 2. Description of ionic- and covalent bonds as a different (dichotomous) or a similar model | Ho 2 : Dichotomous explanation of ionic- and covalent bonds | Hi 2 : Quantum mechanical explanation for consistency |
| The student explains why ionic- and covalent bonds are formed with dichotomous explanatory models. Example of student answers: | The student describes why both ionic- and covalent bonds are formed with a similar, hierarchical explanatory model by mentioning all of the following: | |
| 1. By transfer or sharing of electrons. | 1. Ionic and covalent bonds are formed because of electrostatic forces, even if only the attraction force between oppositely charged particles is mentioned when describing the formation of ionic bonds; | |
| 2. When two or more non-metal atoms bond they form a covalent bond. | 2. The bond formation results in a lower energy level; | |
| 3. When one metal and one non-metal atom bond they form an ionic bond. | 3. The student can also describe the difference between ionic- and covalent bonds. | |
| 3. Description of the formation of covalent bonds | Ho 3 : Simple description of the formation of covalent bonds | Hi 3 : Quantum mechanical description of the formation of covalent bonds |
| Describes why covalent bonds are formed with a simple description model, without showing any understanding of quantum mechanical principles. Example of student answers: | The student describes why covalent bonds are formed by connecting the minimum-energy principle, electrostatic forces and the octet rule by describing all of the following: | |
| 1. The student describes that the electrons are forcing atoms to stick together. | 1. The student describes how electrostatic forces/attractions between particles results in chemical bond formation; | |
| 2. Atoms share electrons to reach noble gas structure. | 2. The student also mentions that covalent bond formation results in a lower energy level; | |
| 3. Covalent bonds are formed since the difference between the electronegativity between the atoms is zero. | 3. Noble gas formation is one way of reaching a lower energy level. | |
| 4. Description of the formation of ionic bonds | Ho 4 : Simple description of the formation of ionic bonds | Hi 4 : Quantum mechanical description of the formation of ionic bonds |
| The student describes why ionic bonds are formed with a simple description model, without showing any understanding of quantum mechanical principles. Example of student answers: | The student describes why ionic bonds are formed by connecting the minimum-energy principle, electrostatic forces and the octet rule by describing all of the following: | |
| 1. Ionic bonds are formed because of transferring or receiving electrons. | 1. The student describes how ionic bonds are formed because of electrostatic attractions between oppositely charged ions; | |
| 2. Ionic bonds are formed because atoms strive to achieve noble gas structure. | 2. The student also mentions that ionic bond formation results in a lower energy level; | |
| 3. Ionic bonds are formed because oppositely charged ions attract each other. | 3. Noble gas formation is one way of reaching a lower energy level. | |
| 5. Description of chemical bonds as a continuum scale | Ho 5 : Chemical bonds are not described as a continuum scale | Hi 5 : Chemical bonds are described as a continuum scale |
| The student knows that different atoms have different electronegativity but cannot describe the connection between electronegativity and the formation of nonpolar covalent bonds, polar covalent bonds and ionic bonds as a continuum scale. | The student can describe the connection between electronegativity and the formation of nonpolar covalent bonds, polar covalent bonds and ionic bonds as a continuum scale. | |
Statistical analysis
Wilcoxon matched-pairs signed rank test was used to compare the median of the response groups after the pretest and the posttest. This test was considered appropriate because the differences between paired individuals did not meet the assumption of a normal distribution. Correlation between the ranking of response group and final grade in the chemistry course was assessed using Spearman's rank testing. The statistical tests were performed using GraphPad Prism version 10.2.3.Ethical considerations
The study adhered to the ethical guidelines outlined by the Swedish Research Council (2017). Before participating in the research project, the students and their parents were informed that they could choose to decline or withdraw from participating at any time. Additionally, it was communicated that all collected data would be anonymized. Furthermore, the students and their parents were informed that the four chemistry lessons would be video recorded, and if the videos were shared outside the lesson study team, the students' faces would be blurred. The video recordings were not used in the present study since the focus of the students’ learning process did not require analysis of the recorded lectures. In the educational setting, the first author served as a researcher rather than a teacher and had no personal relationship with the participating students. Signed informed consent was obtained from all participants and their parents. To ensure that all students could benefit from the revised version of Lesson 1, the students was provided with access to the final version of the lesson in PDF format following the completion of the posttest. Additionally, the content of the final version of Lesson 1 was revisited with all students before their completion of a graded test on chemical bonding.Results
Lesson study results of Lesson 1
To elicit student understanding about the content of Lesson 1, the 75 students in group A, B, and C were asked to respond to the question prompt “why do atoms form chemical bonds?”, after completing Lesson 1. The student's responses were divided into six themes (see Table 5). In student group A, the majority of the students (74%) stated that chemical bond formation results from atoms striving to reach a lower energy level. 63% and 75% of students in groups B and C, respectively, provided similar answers. Among the students in group A, only three (11%) mentioned that bond formation occurs due to both attractive and repelling forces, while in group B, two students (8%) mentioned the same. However, 16 students (67%) in student group C mentioned both attractive and repelling forces as causes of bond formation, indicating that this student group had an easier time understanding the lesson content in depth. Conversely, in student group A, more students (26%) mentioned attraction as the only electrostatic force contributing to bond formation, compared to student groups B and C (4% and 0%, respectively). Furthermore, no students in student group A mentioned the charge of different particles and how these particles interacted with each other through attraction or repulsion. However, these details were mentioned by 8% and 13% of students in student groups B and C, respectively.| Themes found in the student answers | Examples of student answers | Number (percent) of students in group A (n = 27) | Number (percent) of students in group B (n = 24) | Number (percent) of students in group C (n = 24) |
|---|---|---|---|---|
| To reach a lower energy level and/or higher stability | To reach a lower energy level and/or higher stability | 20 (74%) | 15 (63%) | 18 (75%) |
| To reach a lower energy level, which they do when they form Noble gas structure | ||||
| Attraction is the only central force in bond formation | To reach a lower energy level and/or higher stability, which they do when two atoms attract each other | 7 (26%) | 1 (4%) | 0 (0%) |
| To reach a lower energy level, which they do when an atom's nucleus attracts another atom's electrons. | ||||
| Attraction occurs between electrons | ||||
| Atoms get more energy by attracting each other | ||||
| Attraction and repulsion are central forces in bond formation | To reach a lower energy level, which they do when the attractive and the repulsive forces are equal | 3 (11%) | 2 (8%) | 16 (67%) |
| To reach a lower energy level, which they do because of the attractive and the repulsive forces between particles | ||||
| Because of electrostatic attraction and electrostatic repulsion | ||||
| Attraction between differently charged particles is central in bond formation | To reach a lower energy level, which they do when an atom's nucleus/protons attract another atom's electrons. | 6 (22%) | 8 (33%) | 8 (33%) |
| Because of attraction between positive charges and negative charges. | ||||
| Attraction between differently charged particles and repulsion between equally charged particles is central to bond formation | To reach a lower energy level, which they do because of attraction between oppositely charged particles and repulsion between negatively charged particles | 0 (0%) | 2 (8%) | 3 (13%) |
| Because of attraction between particles with opposite charges and repulsion between particles with equal charges | ||||
| The answer indicates that the student does not understand why atoms form bonds | Attraction occurs between electrons | 2 (7%) | 1 (4%) | 1 (4%) |
| Atoms get more energy by attracting each other | ||||
| Atoms want each other's charge to get complete | ||||
| To get a charge, then the particles attract or repel each other | ||||
The data in Table 5 indicate stark differences for some themes in the different student groups. Since there was no significant difference between the student groups regarding previous knowledge about chemical bonding (data not shown), it is possible that the changes in Lesson 1 (as described previously) led to a deeper understanding of the lesson content. However, a larger cohort is needed to fully address this question.
Pre- and posttest
This section of the results addresses the question to what extent students can internalize a hierarchical knowledge discourse about chemical bonding and, thus, if a force-based teaching approach is too demanding for 16–17-year-old students at an upper secondary school level. Students’ pre- and posttests responses about chemical bonding were analyzed by using a theoretical thematic analysis as described previously. The categories identified during the analysis were (1) overall description of chemical bonding; (2) description of ionic- and covalent bonds as a different (dichotomous) or a similar model; (3) description of the formation of covalent bonds; (4) description of the formation of ionic bonds; (5) description of chemical bonds as a continuum scale. Each of the categories could be further divided into horizontal and hierarchical knowledge discourses. The categories and subcategories are described in Table 4.Based on the prevalence and frequency of each subcategory identified in the pre- and posttests, the students’ descriptions were further categorized into six different response groups (response groups 1–6). The response groups were analyzed as ordinal data, wherein the student answers were categorized mostly by a hierarchical discourse in group 1 and least by a hierarchical discourse in group 6. In response group 1 and 2, students’ answers were exclusively characterized by hierarchical discourse. However, while students in response group 1 utilized all hierarchical subcategories (Hi1–Hi5) described in Table 4, those in response group 2 were unable to answer all test questions correctly, using neither horizontal nor hierarchical discourse for certain subgroups. Nevertheless, despite not completing all sections of the test questions accurately, students in response group 2 used only a hierarchical discourse in their explanations for 2–3 categories in Table 4. In response group 3, the students’ answers were categorized by both horizontal- and hierarchical discourse, however, the hierarchical discourse was more prevalent. Like response group 3, the student's answers in response group 4 contained both a horizontal- and a hierarchical discourse but the horizontal discourse was more commonly expressed. The students categorized in response group 5 used only a horizontal discourse when answering the test questions. Finally, response group 6 did not know enough about chemical bonding to be able to answer the test questions by using either a horizontal or a hierarchical discourse. The data in Fig. 4 show the categorization of students’ responses in response groups 1–6 based on the data in the pre- and posttest. The results in Fig. 4 represent 67 students who completed both the pretest and the posttest. The data generated by students who did not complete both tests were excluded from this part of the study. Fig. 4 shows that before starting up the lessons about chemical bonding most of the students (98.5%) displayed solely horizontal knowledge structure or no knowledge at all about chemical bonding (response group 5 and 6, respectively). Only one student (1.5%) demonstrated some degree of hierarchical understanding about chemical bonding when writing the pretest, explaining that the attraction between oppositely charged particles results in chemical bonding and reduction in potential energy. Thus, this student answer was categorized within response group 4. The results from the posttest reveal that 59.7% of the students demonstrated solely (response group 1 and 2) or predominantly (response group 3) hierarchical knowledge structure, indicating that most students were able to understand the force-based approach of chemical bonding by using an abstract and specialized language. The students with neither hierarchical nor horizontal knowledge structure about the chemical bonds in response group 6 decreased dramatically from 23.9% to 6.0% after completing the posttest. Furthermore, the students with solely horizontal knowledge structure (response group 5) decreased by 26%, from 74.6% of the study group when doing the pretest to only 19.4% when doing the posttest.
 | ||
| Fig. 4 Categorization of 67 students based on the results of the pre- and posttest. The categories are based on Bernstein's theory of vertical horizontal and vertical hierarchical discourse (Bernstein, 1999) and are derived from Table 4. | ||
To fully address research question 1, to what extent a lesson improved by a lesson study develops a vertical hierarchical knowledge discourse about ionic bonds, nonpolar and polar covalent bonds among upper secondary school students, the students’ posttest responses were first consolidated into three groups: response group 1–3 – solely or mostly hierarchical discourse; response group 4–5 – solely or mostly horizontal discourse; response group 6 – neither hierarchical nor horizontal discourse. The percentage of students from each student group (ABC) in each of these consolidated response groups were compared and visualized Fig. 5. The results show that the hierarchical knowledge discourse increased among the students during the study. When analyzing the posttest, Student group A, which was first introduced to Lesson 1 about chemical bonding, contained an equal distribution of students in response groups 1–3 and response groups 4–5, which included students showing solely or mostly a hierarchical discourse and students showing solely or mostly a horizontal discourse, respectively. However, when analyzing the posttests from student groups B and C, the hierarchical discourse increased at the expanse of a horizontal discourse among the students. These results indicate that a lesson study, as a method for evaluating and improving lessons, is an efficient way to enhance student learning and to help student develop a hierarchical discourse.
 | ||
| Fig. 5 Categorization of 67 students based on the results of the posttest. The categories are based on Bernstein's theory of vertical horizontal and vertical hierarchical discourse (Bernstein, 1999) and are derived from Table 4. Among the participated students, student group A completed the lessons about chemical bonding first. After improvement of Lesson 1 by the lesson study team, student group B took part of the lesson. After a final revision of Lesson 1, student group C participated at Lesson 1. | ||
To investigate if there was a statistically significant difference between the scoring of the students’ knowledge structure before and after the education about chemical bonding, a Wilcoxon matched-pairs signed rank test was conducted. The test shows that the students presented a significantly higher degree of a hierarchical knowledge discourse at the posttest when compared to the pretest (W = −1692, p < 0.0001; Fig. 6). These results indicate that it is possible for 16–17-year-old students to improve their discourse about chemical bonding, from being able to understand chemical bonding by using a horizontal discourse, in which chemical bonds are described with everyday language without containing a full scientific explanation of why chemical bond formation occurs, to a hierarchical discourse based on general scientific theories spanning over both physics and chemistry.
 | ||
| Fig. 6 Categorization of 67 students after analyzation of the pre- and posttests. The response groups are based on Bernstein's theory of vertical horizontal and vertical hierarchical discourse (Bernstein, 1999) and are derived from Table 4. The data are shown as the mean ± SD. The statistical significance was evaluated by Wilcoxon matched-pairs signed tank test. **** p < 0.0001. | ||
To answer research question 2, if a higher degree of hierarchical knowledge discourse about chemical bonding correlate with higher final grades in upper secondary school chemistry, a Spearman's correlation test was conducted between the response groups from the posttest and the students’ final grades at the end of the upper secondary school chemistry course. The test revealed a strong positive correlation between final grades and degree of hierarchical discourse (p < 0.0001; r = 0.710).
Discussion
Designing the lesson content
The issues of understanding the occurrence and properties of materials, and further the transformation of energy in chemical reactions, are defined as core content in the upcoming Swedish curriculum for chemistry at the upper secondary level (Swedish National Agency for Education, 2024). To fully meet this content without introducing misconceptions that can impede learning, the focus of education should be on the tendency of atoms to reach the lowest possible energy (stabilization), which can be achieved when there is a dynamic equilibrium between attractive and repelling forces. Although some studies have suggested that a force-based approach grounded on quantum mechanical principles might be overly demanding at a high school level (Levy Nahum et al., 2008; Stevens et al., 2010), the results from this study indicate that 16–17-year-old learners can internalize this kind of knowledge (Fig. 4 and 6).During the design of the lessons for this study, the goal of the lesson study team was to provide a scientific explanation of the main factors behind the occurrence of chemical bonds. The lessons focused on using a uniform force-based model based on Coulombic interactions between the nuclei of atoms and their outer electrons. The lesson content also included two coexisting explanatory models. First, the minimum energy explanatory principle, which explains the driving force behind bond formation, as physical systems evolve towards lower energy configurations. Second, the octet framework was used to explain bond formation, mainly by exemplifying formations of covalent and ionic bonds. Some studies have suggested that the octet framework should be avoided in chemistry education (Joki et al., 2015) or at least be seen as a guideline rather than an explanatory principle for bond formation since it might impede chemistry learning at higher levels if it is overgeneralized (Levy Nahum et al., 2008). On the other hand, research have shown that learners may possess multiple coexisting explanatory schemes as a mental toolkit, which can be applied to the same concept area (Taber, 2000). In this study, the lecturing teacher needed to repeatedly state that octet formation is neither a driving force (or something “desirable” for the atoms) nor an explanation of why atoms form chemical bonds. While designing the lessons, the lesson study team believed that the octet framework, in combination with the Bohr model, could serve as a mnemonic device to help students understand the basis of the learning content and subsequently grasp Lewis structures. It is also plausible to assume that the students have previously encountered the octet framework, making it important to combine their prior knowledge with more details, leading to a more valid explanation of how and why chemical bonds occur.
According to Bernstein (1999) one way to make specialized language more accessible to students is when segments of horizontal discourse are recontextualized and inserted in the content knowledge of school disciplines. This can typically be found in schools placed in the lower levels of national external assessment and whose students come from social sectors with fewer resources. The practices of these schools are, moreover, often characterized by a lower level of conceptual demand, i.e., a lower level of scientific complexity and cognitive skills expected by the students (Ferreira and Morais, 2018). This might, however, restrict students from accessing the theoretical knowledge that is highly valued by society and cannot be acquired elsewhere than in the schools (Young, 2009). Also, Bernstein (1999) is doubtful regarding integration of a horizontal discourse in education, since segmented and simplified knowledge cannot provide students with the deep knowledge that characterizes a vertical hierarchical knowledge structure. Our results suggest that if these explanatory models are linked to a scientific (force-based) approach, students will be able to comprehend the hierarchical discourse within chemistry education and, thus, a higher level of conceptual demand. This will at least allow the students an opportunity to develop a more abstract and, thus, more “powerful” knowledge (McLean et al., 2013, p. 267), which gives rise to a higher level of critical thinking, tools to analyze the world, and “voice themselves” (Bourne, 2003).
Lesson study results of Lesson 1
After the first lesson on chemical bonding, the students were instructed to write a summary explaining why atoms form chemical bonds. The results of the lesson study indicate that student group C showed a greater level of a vertical hierarchical discourse in their responses to the question “Why do atoms form chemical bonds?” (Table 5). Thus, these results indicate that collaboration between chemistry teachers through a lesson study contributes to enhanced learning of chemical bonding. This aligns with previous research indicating improved student learning outcomes through the implementation of lesson study within the natural sciences (Jansen et al., 2021; Wang et al., 2022).Results of pre- and posttest
After analyzing the pre- and posttests, it became obvious that several knowledge elements are required to build a force-based mental model based on a hierarchical discourse: attraction and repulsion as simultaneous electrostatic forces at a specific distance between atoms, and the minimum energy explanatory principle. Additionally, students must connect the octet framework to the force-based explanatory principle and see it as one way to reach lower potential energy. Following the posttest, most students could demonstrate all these knowledge elements, even though some used anthropomorphic descriptions such as “The atoms want to reach a lower energy level, which they do when the attractive and repulsive forces are equal”. If a student demonstrated a similar description, they were often categorized in response group 3, showing both horizontal and hierarchical understanding, but predominantly hierarchical understanding. This type of anthropomorphism regarding the “preferences” of atoms has been observed frequently in studies investigating students’ explanations of chemical reactions (see for example Nicoll, 2001; Weinrich and Talanquer, 2015; Dood et al., 2020). Even if anthropomorphic descriptions can be seen as surface-level (horizontal) reasoning it is likely to think that it may not cause any problem in the learning process of chemical bonds if the students can demonstrate a more complex (hierarchical) reasoning as well, such as force-based explanation of why atoms form chemical bonds.The results of the Spearman test indicate that students who understand chemical bonding from a quantum mechanical perspective will succeed in getting higher grades in upper secondary school chemistry. However, it is possible that the students capable of internalizing a hierarchical discourse also study harder and would have reached a higher degree in the chemistry course, even if they had a traditional education about chemical bonding.
Despite 59.7% of the students demonstrating primarily hierarchical knowledge structure during the posttest, a significant number of students (27 out of 67) in this study exhibited primarily horizontal knowledge. Given that the Swedish curriculum, chemistry textbooks for upper secondary students (Bergqvist et al. 2013), and chemistry teachers at upper secondary schools (Bergqvist and Chang Rundgren, 2017) typically do not present chemical bonding as a force-based approach, it may not pose a risk for students to fail chemistry courses at an upper secondary school level if only a horizontal discourse is represented during chemistry tests. However, a hierarchical knowledge structure can likely provide a deeper insight and a genuine scientific explanation for the formation of chemical bonds. This, in turn, would enable students to better understand the rest of the chemistry course (including chemical equilibrium, thermodynamics, molecular structure, and chemical reactions), as well as chemistry education at higher levels. Moreover, it may lead to better retention of chemistry knowledge over time. However, these assumptions need further investigation.
Limitations and further directions
The data in the present study is based on written tests, which may only represent a part of the students' knowledge. Using pre- and post-tests in combination with interviews would provide a deeper insight into the students' knowledge structures and perhaps generate more reliable data. The students in each group took the tests simultaneously in one classroom. Task-based interviews closely linked to the lectures could be used as another research method to gain knowledge about the students' existing and developing subject knowledge and thoughts when solving chemical tasks (Maher et al., 2014). However, due to its time-consuming nature, this method would only provide information about a limited number of students, making the results less generalizable.Assessing students' learning immediately after an intervention provides limited knowledge. A delayed posttest would help determine how students' knowledge structures change over time (Ding and Harskamp, 2011). Conducting a delayed posttest following an intervention on chemical bonding, particularly based on quantum mechanics, could offer insights into the intervention's impact on students' learning and its long-term effectiveness. It helps determine whether students have retained the fundamental concepts and principles taught during the intervention, which goes beyond rote knowledge. Moreover, by assessing students’ understanding one year after the intervention, it is possible to evaluate the extent to which they can utilize these concepts to solve new problems or analyze unfamiliar situations, thus indicating the transferability of the knowledge to new areas.
Conclusions
This paper presents a study of how 16–17-year-old students in upper secondary school learn about chemical bonding. The study found that students with limited previous knowledge of chemistry can learn about chemical bonding in the context of quantum mechanical principles. After the lessons about chemical bonding, most of the students used advanced reasoning and a vertical hierarchical knowledge discourse, which showed a positive correlation with higher final grades in upper secondary school chemistry. Even taking into consideration the relatively small student group it is reasonable to assume that internalization of a hierarchical knowledge discourse leads to a deeper understanding of natural science and benefit higher studies and critical thinking.The group of students who received a lesson after two iterative revisions provided more detailed explanations of why atoms form chemical bonds compared to the other groups. This suggests that collaboration between chemistry teachers through a lesson study can lead to improved learning of chemical bonding.
Data availability
Data collection from the participating students and the teachers are not available to access due to ethical reasons.Conflicts of interest
There are no conflicts to declare.Appendix: pre- and posttests
Pretest
1. When atoms and ions bind to each other, new substances are created. Which of the bonds below have you already heard of? (Circle the ones you already know).a. Ionic bond
b. Covalent bond
c. Polar covalent bond
d. Metallic bond
2. Can you describe how one or several of the bonds above are formed? Explain using words and/or pictures.
3. Why are bonds formed? Is there some kind of force or other reason that makes atoms bind together?
4. Do you know the concept of “electrostatic attraction”? If yes, explain what it means.
5. Draw a picture/model of how you think two hydrogen atoms bind together by a covalent bond.
6. Draw a picture/model of how you think the ions in magnesium oxide (MgO) are bonded together.
7. What is the difference between a covalent bond and an ionic bond?
8. Is there any similarity between a covalent bond and an ionic bond?
Posttest
1. Hydrogen gas, (H2), has covalent bonds. Explain briefly (in one sentence), why a covalent bond is formed, in this case between two hydrogen atoms.2. Explain briefly (in one sentence) what holds the two atoms in H2 and HCl together. You may draw a model if you like.
3. The figure below (Fig. 7) describes an energy curve for two atoms coming together. Explain what happens at the different points A–C and compare the forces involved.
 | ||
| Fig. 7 An energy curve for two atoms coming together. | ||
4. The figure below (Fig. 8) shows an energy diagram.
 | ||
| Fig. 8 An energy diagram of a sodium atom and a chlorine atom coming together. | ||
a. What is the driving force that makes a sodium atom transfer an electron to a chlorine atom in step 1?
b. What is formed in step 1?
c. What happens in stage 2?
d. Why is energy lost in step 1 and 2?
5. What is the difference between an ionic compound and an ionic bond?
6. When a magnesium ribbon burns in oxygen a new compound is formed: magnesium oxide (MgO). What bond is formed when the magnesium ribbon burns in oxygen? Motivate your answer.
7. When chlorine gas and hydrogen gas react hydrogen chloride (HCl) is formed. What bond is created when HCl is formed? Motivate your answer.
8. The figure below (Fig. 9) shows two chemical substances that we call X and Y. These substances have different bonds.
 | ||
| Fig. 9 Two chemical substances (called X and Y) with different chemical bonds. | ||
a. What bond is holding the particles together in X and Y respectively.
b. Is there a common physical force that creates the different bonds?
c. State which particles holds X together? Explain how they hold X together.
d. State which particles holds Y together? Explain how they hold Y together.
9. Chlorine is a toxic gas that is formed by two chlorine atoms binding together.
a. Write a reaction that shows how chlorine gas is formed.
b. Write a Lewis structure for chlorine gas.
c. Are the chlorine atoms bonded together by a single, double, or triple bond?
10. Which of the descriptions below best describe the bond in hydrogen gas best? Motivate your answer.
H:H
H:H
11. Which of the descriptions below best describe the bond in hydrogen fluoride best? Motivate your answer.
H:F
H:F
H:F
12. Write the following particles in order of increasing stability (least stable first): Mg, Mg2+, Mg6−. Explain your reasoning.
13. Are the bonds in the water molecule non-polar covalent bonds, polar covalent bonds or ionic bonds? Motivate your answer.
14. Consider the figure below (Fig. 10).
 | ||
| Fig. 10 Two atoms approaching each other. | ||
a. Why is the grey color darkest in the middle, closer to the red nucleus?
b. Why is the structure of the grey fields different in step 1 and 2?
c. What happens in step 3?
Acknowledgements
Special thanks to Dr Carin Birgersson, Mr Sven Dahlberg, Mr Fredrik Moberg, and Mrs Frida Palmqvist, the teachers who welcomed the first author into their chemistry classes and engaged in thoughtful didactic and scientific discussions. I would also like to thank Dr Anne Solli and Dr Alexina Thorén Williams for their support and advice during the start-up of this project. Thanks to Mrs Lisa Fondelius, for reading the manuscript. This research was funded through a scholarship from the Swedish National Agency for Education.References
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