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

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

21 usually met, as students struggle to understand chemical bonding concepts and processes (Namibia. MoEAC, 2015). This failure warrants exploring a novel pedagogic intervention for the topic of chemical bonding. Undertaking the intervention necessitated first reviewing the syllabus’ objectives.

The Namibian Physical Science syllabus has both general and specific objectives. The general objectives are broad, and highlight what learners are expected to know or understand upon the completion of the topic (Namibia. MoEAC, 2015). For example, expecting learners to understand different types of chemical bonding is a general objective, because it is only achievable after types of chemical bonding are taught. Specific objectives state in detail, using action verbs (such as describe, list, identify, etc.), what learners are expected to do (Namibia. MoEAC, 2015). For example, expecting learners to describe and distinguish between covalent and ionic bonding is a specific objective, because it specifically requires them to give the details of, and the differences between, these two bonding types. Table 2 shows the general and specific objectives of the JS Physical Science syllabus for chemical bonding.

Table 2. General and specific objectives of the JS Physical Science syllabus on chemical bonding (Namibia. MoEAC, 2015, pp. 31-32)

Topic General objectives:

Learners will:

Specific objectives:

Learners should be able to:

2.4 Chemical bonding  understand the different types of chemical bonding

 describe and distinguish between covalent and ionic bonding as different types of bonding and relate bonding to position (group) of elements in the Periodic Table

2.4.1Covalent bonding (revised from Grade 8)

 know how to illustrate covalent bonding as the sharing of electrons when atoms combine

 describe how non-metal atoms combine with other non-metal atoms by sharing electrons in their outer shells with the result that both atoms achieve full outer shells

2.4.2 Ionic bonding /electrovalent bonds Note:

 electrons are indicated by crosses or dots

 know how to illustrate ionic bonding as the transfer of electrons to form oppositely charged ions which attract electrostatically

 describe how the reaction between a metal and a non-metal results in the transfer of electrons from metal atoms to non-metal atoms so that both achieve full outer shells and form positive ions (cations) and negative

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 electrons from different atoms should be differentiated by crosses and dots

 arrows should be used for electron transfer

 transferred electrons should be indicated only once in the anion and not in the cation and the anion

 only the outer shell will be indicated in the bonding sketch

ions (anions) respectively

 predict the positive and negative charges of ions (in terms of attained noble gas electronic structures)

 define ions as atoms with a net electric charge due to the loss or gain of one or more

electrons (e.g. cations have lost electrons and anions have gained electrons in order to attain noble gas structure)

 draw Bohr structures of ionic compounds

 explain ionic bonding as the electrostatic attraction between oppositely charged ions (cations and anions)

 describe the lattice of an ionic compound as a regular arrangement of alternating positive and negative ions

 write the formulae of ionic compounds including polyatomic ions (i.e. SO42-; NO3-; CO32- ; NH4+; HCO3-; OH^-)

In addition to the general and specific objectives for chemical bonding in the Physical Science syllabus, the syllabus provides guidelines as to how learners are expected to illustrate concepts in the topic. These guidelines are provided for uniformity in how Physical Science teachers approach the topic as most learners in Namibia have difficulty illustrating chemical bonding (Namibia. MoEAC, 2015). For this study, this guideline needed consideration;

because the study is based in Namibia, disregarding it might have negatively impacted on the validity of this study, and disadvantaged the learners in their examinations. The requirements of the syllabus, as provided by the Ministry of Education, Arts and Culture (2015, p. 32), include:

 “The nucleus has to be indicated, and a small line to the outside of an atom is drawn from it to write the number of protons and neutrons.

 Electrons have to be indicated by crosses or dots only.

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 Electrons from different atoms should be differentiated by using dots and crosses.

 The overlaps of shells in covalent bonding should be used.

 All shared electrons in covalent bonding should be indicated in the overlap.

 Only the outer shells should be used in the bonding sketch of both ionic and covalent bonds.

 In ionic bonding, arrows should be used to indicate electron transfer from a metal atom to a non-metal atom.

 Transferred electrons should be indicated only once, in the anion, and not in both the anion and the cation.”

It is possible that the way the syllabus expects chemical bonding to be taught contributes to the challenges faced by learners. For example, Gilbert and Treagust (2009) argue that interpretive frameworks developed by chemistry experts may cause novices to focus on incidental aspects of the representation used rather than on the main aspect. They argue that some curricula present meaningless features. It is possible that the Namibian JS Physical Science syllabus also presents meaningless features that have the potential to impact negatively on learners’ sense-making of chemical bonding. Despite this possibility, this study does not defy the curriculum’s specifications with regards to illustrating chemical bonding to learners, as that would have meant that learners’ participation in the study would have disadvantaged them, thus raising ethical concerns.

As evident from Table 2, knowledge of chemical bonding at the Namibian JS phase is represented mainly at sub-microscopic and symbolic levels, which Johnstone (1982) identifies as most challenging. This is noticeable, for example, in the stipulations made by the JS Physical Science syllabus on molecules and how they should be presented to learners (Namibia. MoEAC, 2015). Much of the chemical bonding knowledge in the Physical Science syllabus is sub-microscopic as it concerns microscopic particles of matter such as atoms, ions, and molecules that are non-observable. For instance, the Physical Science syllabus classifies molecules of covalent compounds as either diatomic or polyatomic. It defines a diatomic molecule as “a molecule made up of two atoms bonded together covalently”, and a polyatomic molecule as “a molecule made up of more than two atoms bonded covalently”

(Namibia. MoEAC, p. 31). Further, it classifies diatomic molecules as either homonuclear (made up of two atoms of the same elements) or heteronuclear (made up of two atoms from different elements). Examples of homonuclear molecules are H2, O2, N2, and diatomic

24 molecules of group 7 elements such as F2, Cl2, Br2, and I2, while examples of heteronuclear molecules are HF, HCl, and CO molecules. Polyatomic molecules such as CO2, CH4, H2O, and NH3 are heteronuclear, while O3 and S8 are homonuclear. Moreover, some aspects included in this knowledge are symbolic because there are symbols and subscripts used to represent ideas/information. This has the potential to add further difficulty to making sense of knowledge of chemical bonding, as these symbols and subscripts are usually complex to learners (Johnstone, 1982).

Knowledge at the sub-microscopic level, such as of molecules, and at the symbolic level, such as of formulae of compounds, covered by the Namibian Physical Science syllabus, may only be effectively accessed by students if they have developed mental models, as Nimmermark (2014) suggests. The syllabus also suggests that simple physical models may be used to illustrate both the Bohr structure of the first 20 elements in the periodic table, and that atoms bind to form molecules (Namibia. MoEAC, 2015). However, the syllabus does not discuss this in any further detail. As Johnstone (1982) suggests, physical models help to present the sub-microscopic level in a macroscopic way, in order to make chemical bonding concepts more explicit to learners. Therefore, this study also considered physical models by drawing from the perspectives of Social constructivism, since their use forms an aspect of the visual mode and, together with the verbal mode, might be used to mediate learners’ meaning- making.