Representations including powerful examples and analogies

This aspect of TS-PCK refers to various conceptual representations that a teacher uses in teaching a particular topic; for instance, illustrations, examples, analogies and models, which support teachers in reinforcing a particular concept. When teachers are teaching the basic agricultural chemistry topic of organic compounds, specifically on bonding, they should use examples that are relevant to learners’ lives. According to Roche (2013), basic agricultural chemistry includes teaching learners first about atoms, explaining them with objects or stick models and showing how and why molecules are formed, which then advances into more abstract concepts of chemical bonding and intermolecular bonds. Nahum et al. (2004) hold that for teachers to teach chemistry content well, they need to have an understanding of suitable models to use to help learners

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understand the unseen phenomenon. Furthermore, they clarify that teachers should know how their learners construct their own intellectual models, and how to use the models successfully in their classrooms. Van Driel, Verloop, and de Vos (1998) maintain that using models is part of a teacher’s efforts to represent challenging and abstract concepts in a variety of ways so as to enable their learners have a full understanding of them. Harrison and Treagust (2010) hold that models are crucially important, in that they provide a good link between methods and products of science. As alluded to by Gilbert and Justi (2016), the effective teaching of chemistry requires an individual educator to be strong in his or her understanding of the models that are used in chemistry and why they are used differently in different topics. They further expound that it is also important to know how their learners mentally construct representational models and how they can utilize those models constructively in their classrooms. Lastly, they agreed that teachers who teach chemistry should be acquainted with the use of models in their lessons as some of these models may convey a different meaning to learners if they were misrepresented. Sometimes learners can get confused with models and think that they are just play tools. So although models are an excellent strategy for effective teaching and modelling of chemistry, studies reveal that only few teachers among those with a chemistry major were able to use models effectively (Grosslight, Unger, Jay, & Smith, 1991; Gulyas, Pfefferle, Wolf, & Waitz, 2015). Bachsmann, Wolf, and Waitz (2015) also suggest that the use of models creates a mental image for learners of what matter is and how it is made up. Furthermore some models are of a predictive nature, like an atom, meaning that models can be used to create a mental image for learners to predict how an atom would look. Other models that are often used by chemistry teachers to enable learners to access abstract concepts include balls and sticks to represent molecules to show learners what molecules may look like (Gilbert & Justi, 2016).

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Role playing such as in a game, collaborative learning, or assigning learners for different duties would also enable learners to express their knowledge of processes that takes place in chemistry, because these learners could act a part played by a certain concept, or make an object in clay in a fun environment. Concept mapping is one way that chemistry teachers could link chemistry concepts. Concept maps uses labelled nodes for the representation of certain concepts for learners (Stevenson, Hartmeyer, & Bentsen, 2017). Furthermore, concept mapping allows the identification and categorization of certain concepts, as well as for the teacher and learners to make connections amongst those concepts (Jaafarpour, Aazami, & Mozafari, 2016). According to Govender (2015), the benefits of concept mapping include easy revision of previous work with learners, facilitating learners making connections between terminologies of a particular topic and argumentative sharing of information; all of which open opportunities for critical thinking skills to be developed.

Prain and Waldrip (2006) refer to multiple representations as playing an important role in teaching science effectively. They hold that by using these representations, learners’ curiosity is easily captured and their understanding increases. Rowles and Brigham (2005) note that instructional strategies that work effectively in chemistry are those that do away with memorization of content and focus on comprehension of the whole subject. They believe this also comes through learners’ engagement with classroom activities, and they believe that learners must always be put at the centre of the lesson. Nevertheless, findings by Olaleye (2012) indicate that the most frequently mentioned strategies used by chemistry teachers were teacher explaining, teacher drawing diagrams and plotting graphs, writing notes and demonstrating experiments; all of which support a conventional chalk and talk teacher-centred approach. He added that

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“almost two-thirds of the teachers used oral questions and answers method to assess students’ understanding of a concept and few teachers used project/problem solving and practical modes of assessment to evaluate lesson objectives” (p. 51). Furthermore, the teachers in that study believed that there was a good level of student’s engagement in class activities.