Chemical bonding complexity and teaching approaches

Chemical bonding is a chemistry topic that aids the overall understanding of chemical phenomena by students and scientists (Nimmermark, 2014). This understanding is attainable via knowledge of the chemistry of atoms, molecules, and ions of which substances consist (Gilbert & Treagust, 2009). The chemistry of these particles explains the behaviour and physical properties of the substances we use (Gilbert & Treagust, 2009). However, for students to understand these chemical phenomena is a challenge, as they often have ideas about chemical bonding that are incompatible with scientific perceptions (Ozmen, 2004).

This incompatibility is due to understanding of chemical bonding involving abstract concepts that require both simple and complex explanation models (Harrison & Treagust, 1996). Some of these models include non-observable entities that are often accessible only via imagination (Gilbert & Treagust, 2009). These entities include atoms, ions, and molecules, as well as their behaviours. If learners’ understanding of chemical bonding is inadequate, their subsequent understanding of chemical phenomena is hampered (Nimmermark, 2014).

Even though the knowledge of chemical bonding is considered to be accessible via the understanding of particular chemical concepts, this is often not achieved, as most learners

18 cannot master these abstract chemistry concepts on their own (Gibert & Treagust, 2009).

Addressing this challenge may consider the assertion that effective chemistry teaching can be influenced by the science teacher’s ability to explain abstract and complex chemical concepts and phenomena to the learners (Treagust, Chittleborough & Mamiala, 2003). Hence, a teachers’ inability to effectively convert concepts from their abstract forms into their concrete forms hampers students’ learning of chemistry, as the subject is rich in these abstract concepts (Treagust, Chittleborough & Mamiala, 2003). Improving learners’ sense-making in the topic requires teaching approaches that enable easy conversion of concepts from abstract to concrete forms.

Making the distinction between abstract and concrete forms may be enabled by considering ideas from Johnstone (1982). He initially categorised knowledge of chemistry as either real or representational. Real knowledge refers to the knowledge of things that exist, while a representation refers to conventional symbols and signs used to represent real chemical knowledge (Johnstone, 1982). According to Johnstone (1982), knowledge of things that exist is concrete, while knowledge of conventional symbols and signs is abstract. From these, he identified three levels of representation at which knowledge of chemistry is taught:

macroscopic, sub-microscopic, and symbolic. The full understanding of these representational levels and their justified use in chemistry teaching by teachers can significantly improve learners’ understanding of chemistry topics (Johnstone, 1982). These representational levels, their meanings, and their relationship to each other are illustrated in Figure 1.

Figure 1. The representational levels of chemistry (Adopted from Johnstone, 1982)

19 According to Johnstone (1982), the macroscopic level of representation involves the representation of real, concrete, and observable chemical phenomena. This level of representation is characterised by teaching and learning of tangible, audible, and visible properties and behaviours of matter (Santos & Arroio, 2016). An example of this level of representation is explaining that limewater, scientifically known as calcium hydroxide solution, turns milky after carbon dioxide is bubbled through it. This is likely to be understood by most learners as they can see limewater changing from being colourless to milky (white). However, even the macroscopic level of representation may be challenging to students if suitable practical experiments are not prepared (Nelson, 2002). Nonetheless, as Figure 1 shows, the macroscopic representation is real because the colour change is observable. It is for this reason that learners usually understand knowledge at this level.

The sub-microscopic level of representation involves unobservable real structures and behaviours of microscopic particles of matter (Johnstone, 1982). This representation level is distinct from the macroscopic level in that it represents facts that cannot be observed, and learners are often confused by this (Harrison & Treagust, 1996). The explanation of what happens to limewater particles when carbon dioxide particles are blown through them is an example of this level of representation. The learners may be confused by this knowledge, as they do not see the particles of limewater and carbon dioxide, or how these particles react with each other. Gilbert and Treagust (2009) argue that this level of representation can only be accessed via imagination, which makes it more challenging than the macroscopic level.

They suggest that while learners’ understanding of this representational level may be achieved through language, this is not often accomplished, as language is sometimes imprecise. Imprecise language benefits from the use of the visual semiotic mode to help learners to understand knowledge at the sub-microscopic level of representation (Gilbert &

Treagust, 2009). Gilbert and Treagust (2009) consider the visual mode as having the potential to depict aspects of the model of matter being explained to learners. Therefore, the visual semiotic mode coordinated with the verbal semiotic mode may be a suitable pedagogic approach required to address the challenge of understanding matter at the sub-microscopic and symbolic levels, the latter of which will now be discussed.

The symbolic level of representation involves the use of conventional signs, symbols, and chemical equations (Johnstone, 1982). The knowledge of chemical bonding at this level is distinct from the sub-microscopic level in that it is unreal. Johnstone (1982) clarifies that this level includes the allocation of symbols to atoms either as single particles or in groups, such

20 as in ionic or molecular forms, of signs to represent the electrical charge of particles, and of subscripts to show the number of atoms in ionic or molecular particles. He adds that it includes letters in chemical equations to indicate physical states of entities. This level of representation is most challenging to students because it requires understanding of complex conventions used in symbolic forms (Johnstone, 1982). Writing a balanced chemical equation for the reaction between molecules of carbon dioxide and ions in limewater to produce calcium carbonate, which causes the milky colour, is an example of the symbolic level of representation as shown here: Ca(H2O) 2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l).

Among these three levels of representation, the symbolic level is most challenging, followed by the sub-microscopic level, with the macroscopic level being the least challenging (Johnstone, 1982). Understanding chemistry topics fully is achievable by obtaining chemical knowledge at the sub-microscopic and symbolic levels, because knowledge of chemistry is based mainly on these two levels (Kozma & Russell, 1997). However, accessing these levels of knowledge is often challenging to learners (Johnstone, 1982). Addressing the challenge of chemical bonding for learners might be informed by Johnstone’s (1982) idea that invisible particles can be represented by using the visual mode of communication. Gabel (1998) argues that students have difficulty making links between the three levels of representation. This adds to the difficulty in learning chemistry. Since chemical bonding is an example of a challenging chemistry topic, Johnstone’s (1982) idea of combining the visual and verbal modes for representing related phenomena was considered useful for my action research around the topic of chemical bonding in the Namibian context. The related curriculum will now be reviewed.

2.2.2 The definition and expectations of chemical bonding according to the Namibian