Evidence of chemical bonding facts sense-making

The sense-making of chemical knowledge belonging to this type is more aligned to science, and noticeable in learners using abstract chemical concepts when explaining science phenomena, such as chemical processes and objects (Zimmerman et al., 2009). I found that the number of learners making sense of chemical bonding facts was higher in Cycle 2 than in Cycle 1. I noticed this in many learners using more abstract scientific words in Cycle 2 than in Cycle 1. This confirms the idea that the coordinated visual and verbal semiotic modes have potential to enhance sense-making of science knowledge (Zimmerman et al., 2009). Two

135 themes of chemical bonding knowledge that have attracted the researcher’s attention include the relationship between atoms and molecules, and the bonding process.

(a) Atoms and molecules relationship

First, sense-making of this knowledge was identified from Learner R stating that “before atoms are bonded they are called atoms but after they bond together we say they are a molecule”. He illustrated his idea with a rough bond diagram, shown in Figure 9.

Figure 9. Learner R’s diagram of atoms forming a molecule (observed during a Cycle 2 lesson)

The knowledge of the relationship between an atom and a molecule was evidently a challenge to students. This knowledge is classified as intra-molecular, as it concerns what constitutes a molecule and the processes happening within it (a molecule) (Gilbert & Treagust, 2009). This challenge can be addressed via using multiple representations, such as the combination of the verbal mode and physical models (Gilbert & Treagust, 2009). The combined visual and verbal modes in the form of diagrams, models, and spoken words, used during this cycle (Cycle 2) enhanced learners’ sense-making of this topic. It is also possible that the physical model of a molecule, which could be dismantled into separate models of atoms, has made the explanation of the relationship between atoms and molecules clear, and has subsequently resulted in improved learners’ sense-making.

Second, many learners correctly identified a diatomic molecule from other molecules. This was noticed in Learner Gd saying “diatomic molecules are made from two atoms that are the same… example if two atoms of oxygen bond together, they form a molecule called a

136 diatomic molecule”. Her correct Bohr structure of a diatomic molecule formed by two oxygen atoms is shown in Figure 10.

Figure 10. Learner Gd’s correct bond diagram of a diatomic molecule formed by oxygen atoms (observed during a Cycle 2 lesson)

This excerpt of learner talk and the diagram (Figure 10) confirmed the finding that the learners’ sense-making of the relationship between atoms and molecules, which are abstract concepts of chemical bonding, was enhanced due to the intervention. The two overlapped Bohr diagrams of oxygen atoms are similar in every respect, except that electrons in one atom are indicated with crosses, while in the other atom they are indicated with dots. These therefore confirm that sense-making of the relationship between atoms and molecules had taken place.

(b)Bonding processes

The chemical knowledge gained by learners that is classified as bonding processes in this sense-making type includes the definition of bonding, explanation of valencies, and description of ions. I accessed these data by analysing excerpts of learner talk about processes of chemical bonding that are related to this sense-making type.

Gilbert and Treagust (2009) suggest that a clear definition of chemical bonding should be provided to learners for them to determine if an element is reactive or unreactive. Learners’

understanding of a bonding process was identified in Learner M saying “bonding is when atoms of elements that have incomplete outer shells bind to have full outer shells”. This excerpt was selected because it was clearer than others, as many learners had difficulty expressing their ideas in English. The phrase ‘incomplete outer shells’ is abstract in two ways. First, the everyday meaning of the word ‘incomplete’ is not directly the same as its scientific meaning. The scientific meaning of this word involves an outer shell of an atom not fully occupied by the maximum number of electrons it can hold, while its everyday meaning refers to an activity or event unfinished or partially done. Second, the word ‘outer shell’ can

137 only be understood by a person who has knowledge of electron arrangement in shells in an atom.

Considering excerpts of learner talk about valency in this study was informed by Gilbert and Treagust (2009). They assert that knowledge of valencies of elements is essential for determining the number of electrons involved in a bond, and for deducing and explaining the formulae of compounds formed from chemical reactions. I realised that twenty-two learners understood the valency concept, as they used it when explaining bonding. Among them was Learner F, who said “valency is the electrons in the outer shell that take part in the bond”.

This indicates that they were aware that only some valence electrons (outer shell electrons) may be involved in a bond – and they are called valency. It is therefore possible that learners having this knowledge would have no problem either explaining chemical bonding or deducing the chemical formula of a compound.

Learner Z attempted to distinguish between cations and anions by saying “cations are atoms that lost electrons while anions are atoms that gained electrons”. She further explained that cations are mostly formed by metals, as they have the tendency of losing electrons, while non-metals form anions, as they mostly gain electrons. Accessing this knowledge is crucial, as it is one of the specific objectives in the Namibian Physical Science syllabus. This concurs with Gilbert and Treagust (2009), who assert that knowledge of ions, including their behaviour, contributes to a deeper understanding of the mechanism involved in the chemical reaction between metals and non-metals. Hence, learners would likely experience fewer problems understanding chemical reactions once they have acquired this knowledge.