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David F. Treagust a; Gail Chittleborough a; Thapelo L. Mamiala aa Science and Mathematics Education Centre, Curtin University of Technology, GPO Box U1987, Perth, WA6845 Australia; e-mail: [email protected].

Online Publication Date: 01 November 2003

Treagust, David F., Chittleborough, Gail and Mamiala, Thapelo L.(2003)'The role of submicroscopic and symbolicrepresentations in chemical explanations',International Journal of Science Education,25:11,1353 1368

10.1080/0950069032000070306http://dx.doi.org/10.1080/0950069032000070306

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International Journal of Science Education ISSN 09500963 print/ISSN 14645289 online 2003 Taylor & Francis Ltdhttp://www.tandf.co.uk/journals

DOI: 10.1080/0950069032000070306

INT . J. SCI . EDUC ., NOVEMBER 2003, VOL . 25, NO . 11, 13531368

RESEARCH REPORT

The role of submicroscopic and symbolicrepresentations in chemical explanations

David F. Treagust, Gail Chittleborough and Thapelo L. Mamiala,Science and Mathematics Education Centre, Curtin University of Technology, GPO Box U1987, Perth, WA 6845 Australia;e-mail: [email protected]

Chemistry is commonly portrayed at three different levels of representation macroscopic, submicroscopic andsymbolic that combine to enrich the explanations of chemical concepts. In this article, we examine the use of submicroscopic and symbolic representations in chemical explanations and ascertain how they providemeaning. Of specific interest is the development of students levels of understanding, conceived as instrumental(knowing how) and relational (knowing why) understanding, as a result of regular Grade 11 chemistry lessonsusing analogical, anthropomorphic, relational, problem-based, and model-based explanations. Examples of both teachers and students dialogue are used to illustrate how submicroscopic and symbolic representationsare manifested in their explanations of observed chemical phenomena. The data in this research indicated thateffective learning at a relational level of understanding requires simultaneous use of submicroscopic andsymbolic representations in chemical explanations. Representations are used to help the learner learn; however,the research findings showed that students do not always understand the role of the representation that isassumed by the teacher.

Introduction

The effectiveness of school chemistry teaching is dependent on the teachers abilityto communicate and explain abstract and complex chemical concepts, and on thestudents ability to understand the explanations. Expert chemistry teachers presentnew information at an appropriate level for the learner, make use of relevant

explanatory artefacts, build on the knowledge and concepts that students alreadyunderstand, and provide students with all the information that they need to knowwithout being beyond their grasp or over-simplifying the content (Treagust andHarrison 1999). In this article, we examine the use of submicroscopic and symbolicrepresentations in chemical explanations, and ascertain what they add to explana-tions and how they provide meaning. The article begins with a discussion of thethree levels of representation in chemistry, an analysis of the types of explanationsused in science classrooms and an examination of different levels of understandingthat are possible with this kind of teaching. This discussion leads to the researchquestion that guides the research: What is the role of symbolic and submicroscopicrepresentations on the comprehensibility of chemical phenomenon, and how dothese representations provide meaning?


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1354 D . TREAGUST ET AL .

Three levels of representation in chemistry

Chemists refer to chemical phenomena at three different levels of representation macroscopic, symbolic and submicroscopic that are directly related to each other(Johnstone 1982). The macroscopic level is the observable chemical phenomenathat can include experiences from students everyday lives such as colour changes,observing new products being formed and others disappearing. In order tocommunicate about these macroscopic phenomena, chemists commonly use thesymbolic level of representation that includes pictorial, algebraic, physical andcomputational forms such as chemical equations, graphs, reaction mechanisms,analogies and model kits. The submicroscopic level of representation, based on theparticulate theory of matter, is used to explain the macroscopic phenomena in termsof the movement of particles such as electrons, molecules, and atoms. Thesesubmicroscopic entities are real but they are too small to be observed, so chemistsdescribe their characteristics and behaviour using symbolic representations toconstruct mental images. We contend, as illustrated in figure 1, that all three levelsof representation are integral in developing an understanding of the chemistryconcepts under investigation.

Students understanding of the role of each level of representation

macroscopic, symbolic and submicroscopic as well as the relationships betweeneach level is often assumed by chemistry teachers who commonly use all three levelssimultaneously. Furthermore, teachers often assume that students can easilytransfer from one level to another (Johnstone 1982). In comparing the perceptionsof experts and novices on a variety of chemical representations, Kozma and Russell(1997) concluded that novices used only one form of representation, and rarelycould transform to other forms, whereas the experts transformed easily. Novicesrelied on the surface features, for example lines, numbers and colour, to classify therepresentations, whereas experts used an underlying and meaningful basis for theircategorization. The study highlighted the need for representational competence,including an understanding of the features, merits and differences of each form, andshowed the significance of computer animations in linking the various representa-tions. Similarly, Copolo and Hounshell (1995) consider this difficult task of mental

Figure 1. Three levels of representation used in chemistry.


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THE ROLE OF REPRESENTATIONS IN CHEMISTRY 1355

transference to be given little consideration, and Johnstone (1982: 379) referred tothe mental gymnastics of slipping and sliding from one level to another as a

necessary skill in understanding chemistry .

Explanations and their relationship to representations

While the macroscopic observable chemical phenomena are the basis of chemistry,explanations of these phenomena usually rely on the symbolic and submicroscopiclevel of representations. Consequently, the ability of students to understand the roleof each level of chemical representation and the ability to transfer from one level toanother is an important aspect of generating understandable explanations. Thesimultaneous use of macroscopic, submicroscopic and symbolic representations hasbeen shown to reduce students alternative conceptions in the teaching and learningof chemical concepts (Russell et al. 1997).

Research studies have shown that it is essential for teachers explanations to bestudent friendly and compatible with the students existing explanatory knowledge(Treagust and Harrison 1999). Dagher and Cossman (1992) identified 10 types of verbal explanations used by science teachers in US junior high school classrooms.Based on research in South African science classrooms, Mamiala and Treagust(2001) expanded Dagher and Cossman s framework to include a more extensiverange of explanations. For the research in this article, the five most prevalent typesof explanations were analogical, anthropomorphic, relational, problem based, andmodel based (see table 1).

Two levels of understanding

Instrumental understanding (knowing how) and relational understanding (knowingwhy) are differentiated by the depth of understanding and the application of knowledge that the learner exhibits (Skemp 1976). The instrumental level reflects arote-learning synopsis where the learner knows a rule and is able to use it; on theother hand, relational understanding reflects meaningful learning in which thestudent knows what to do and why they are doing it. Skemp analysed the merits of each type of understanding, with instrumental being easier and quicker to grasp andproviding immediate rewards and success, whereas relational is more adaptable tonew tasks. The proposed knowledge schema that a student develops at aninstrumental level of understanding would be represented by discrete units, whereas

Table 1. A description of each type of explanation used in the analysis(from Mamiala and Treagust 2001).

Type of explanation Descr iption

Analogical A familiar phenomenon or experience is used to explain the unfamiliarAnthropomorphic A phenomenon is given human characteristics to make it more familiarRelational An explanation that is relevant to the explainees personal experienceProblem based An explanation demonstrated through the solving of a problemModel based Using a scientific model to explain a phenomenon


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at a relational level a student s schema of knowledge would be linked andinterconnected (see figure 2). Skemp emphasized the significance and the subtletyof the differences between the two types of learning, in that the students may knowthe same facts of the subject but their way of knowing is different. Thisepistemological perspective draws attention to the importance of foundationlearning being presented in situ as part of a conceptual structure or schema. Forchemistry, the conceptual schema includes the three levels of chemical representa-tion macroscopic, submicroscopic and symbolic levels of representation. Thedegree of linking between the three levels can provide some insight into theontological knowledge network of the learner. Skemp differentiates two types of learning, whereas Buxton (1978) distinguishes four different stages from instru-mental to relational understanding rote, observational, insightful and formal. It isanticipated that the greater linking between the levels of chemical representationwill enhance students understanding of the concepts.

The inter-relationship between the levels of understanding and the use of

different representations in chemistry is used to investigate the research question:What is the role of symbolic and submicroscopic representations on thecomprehensibility of chemical phenomenon and how do these representationsprovide meaning? The two parts of the research question correspond to two levelsof analysis: the description of the impact of particular representations and theassessment of the potential of the explanation to lead to a deeper understanding of a chemical concept.

Methodology

The data from two independent studies conducted in Year 11 chemistry classes inco-educational high schools in Perth, Western Australia complement each other inthat they both investigated the use and role of explanations in learning chemistry.

Figure 2. Relationship between levels of understanding and levels of chemical representation.


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Study 1 provides a teacher perspective and study 2 provides a student perspective.The studies took place at different high schools, in classes in which students had arange of academic achievement and whose average age was 16 years. The selectionof the schools was based on the teachers volunteering to be involved in the research,the geographic location of the school, and the availability and suitability of classes.Both studies involved student volunteers who had chosen to study chemistry insenior high school.

Study 1: Introductory physical chemistry

The first study involved observations of two chemistry teachers over a 10-weekperiod while they taught topics including the quantitative composition of substances, chemical equations and reacting masses, electron configuration of atoms, structure and bonding of metals, ionic substances, covalent molecularsubstances and covalent network substances, the periodic table and gases. A total of 31 50-minute lessons were observed, 17 with one teacher and 14 with the other. Theteachers made use of a variety of explanations, choosing those most appropriate forthe content and format to suit their students learning styles. The two teachers, whoeach had more than 20 years experience in the classroom, were given a broadoutline of the purpose of the study and were encouraged to teach in their normalstyle, despite the presence of researchers in the classroom. Both teachers wereinterviewed about their choice, justification and delivery of the chemicalexplanations.

Study 2: Introductory organic chemistry

The second study involved the implementation of a model-based teachingprogramme for introductory organic chemistry including topics on the structuresand properties of alkanes, alkenes, alkynes, cyclo-alkanes, nomenclature, isomer-ism, and substitution, addition and combustion reactions. This study, with onechemistry teacher who had over 20 years teaching experience, involved observing24 lessons of two chemistry classes over a 3-week period. The teacher was the headof science at his school and, during the observed lessons, the teaching approachinvolved activities that required the students to build representations of chemicalcompounds using ball-and-stick chemical models. With each class, the studentsworked in pairs, discussing their answers and recording their results as structuralformula representations

Common methodology for study 1 and study 2

Qualitative data sources for both studies came from classroom observations by twoparticipant researchers, interviews with teachers and students, and audio-tapingstudents interactions during group work to identify explanatory occurrences thatinvolved submicroscopic and symbolic representations. The participant researcherstook notes on their observations. In study 1, where possible, both teachers wereinterviewed after chemistry lessons and were asked prepared questions about theirchoice and delivery of chemical explanations. In study 2, six pairs of students were


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randomly selected each lesson to be audio-recorded. In addition, the researchersquestioned students throughout the lessons during group work. The audiorecordings were translated, reviewed and coded for evidence relating to the use of symbolic and submicroscopic representations in learning chemistry.

A variety of explanations using various representations in common chemistrytopics provided a typical sample of chemical explanations. Both studies providedexamples of submicroscopic and symbolic representations in explanations of chemical phenomena to address the first part of the research question. Theexplanations were examined in terms of their intended level of understanding inorder to respond to the second part of the research question. The types of explanations in both studies were based on the framework developed by Mamialaand Treagust (2001) (see table 1).

The authors took on the role of participant observers (Merriam 1998) in orderto document both teachers explanations and students understanding of theseexplanations. Two researchers worked together to cross-check the data and classify

the explanations to ensure an accurate interpretation of the descriptive analyses of the classroom discourses, which were initially based on the classroom observationswith supporting evidence from the interview data.

Results and discussion

Representative examples of the role of submicroscopic and symbolic representationsin chemical explanations have been selected from both studies. The data presentedinclude the concept to be learnt, the type of explanation used, a portion of thetranscript of the learning situation, an analysis of the teaching event in terms of the

submicroscopic and symbolic representations used, and whether instrumental orrelational learning was intended and/or attainable.

Study 1: Introductory physical chemistry

In the first study, five teacher explanations analogical, anthropomorphic,relational, problem based, and model based are described.

Analogical explanation for limiting reagent. The teacher started the lesson by giving abrief definition of the concept of limiting reagent.

Teacher : A limiting reagent is the one chemical in a reaction that determines howmuch of the other chemicals are going to be used up. When you are giventhe following reaction:

MgCO 3 + 2HCl MgCl 2 + CO 2 + H 2 O

1.70 g 1.46 g

and the amounts reacting are as shown. Which one will you say is alimiting reagent?

Student : Multiply 1.46 by 2 and divide by the molecular mass . . .Teacher : Why multiply by 2 . . .?


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A student wanted to multiply by 2 because of the numerical coefficient in HCl; theteacher recognized this issue and introduced an analogy.

Teacher : In a particular community there are 20 male dancers and 20 femaledancers . . . one male is with one female dancer. How many groups willbe on the dancing floor?

Student : Twenty.Teacher : You have one male partnering with one female . . . there will be nobody

sitting. If you have a situation where one male dancer needs two femaledancers, how many groups will be on the dancing floor?

Student : Ten.Teacher : How many people will not be dancing?Student : Ten males.

In this teaching scenario, the teacher used a variety of symbolic representations: theequation, the numerical values of the amounts of chemical compounds, as well asthe analogy to help the students visualize the concept. Analogies are a commonfeature with students everyday language and the teachers ability to use themeffectively contributes towards students understanding of chemical phenomena(Gabel 1998, Thiele and Treagust 1994). According to Dagher and Cossman (1992:364), analogical explanations are when a familiar situation similar to the unfamiliarphenomenon to be explained is used to provide the explanation. A correspondenceis assumed to exist between aspects of the analogical situation and those of theactual phenomenon .

During the post-lesson interview, the teacher commented on the relevance of

the dancing analogy to the students:

Teacher : In Australia, it makes sense because the students look forward to theannual ball. The ball is one of the most eagerly awaited events in one schange of lives, and influences the attitudes, self-esteem, morale andpersonality of the kids.

The teacher was asked why it is necessary to use a lot of explanations for someconcepts?

Teacher : For difficult concepts, I use a lot of questioning techniques and a fair bitof reinforcing techniques. On top of that, the limiting reagent, the excessreagent, types of products and stoichiometry requires much moreexplanation at a ground level. I usually use an analogy and I think it isgoing well with these students.

When asked about the limitations of the analogy, the teacher responded:

Teacher : So even this dancing partners analogy becomes useless because we aredealing with the same boys and girls in different dancing . . . But inchemical reactions, we are dealing with different chemicals in entirelydifferent chemical reactions.


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In the discussion of limiting reagents, the symbolic representation of the equationand the analogy helped to develop the submicroscopic representation of the limitingreagent concept, providing an image of something being left over or, conversely, allused up. The proposed submicroscopic representation to be understood at themolecular level is for the molecules to combine and react on a one-to-two ratio. Theclassroom observations indicated that the students appeared to follow this type of explanation with interest. The teacher s comments indicated that he attributed thesuccess of the analogy to the meaning that the analogy had for these particularstudents. The teacher was aware of the difficulty of the concept and used multiplestrategies to reinforce the concept. When students can apply the concept of limitingreagents successfully, they are able to develop a relational level of understanding of the concept because they are able to transfer from moles to grams to chemicalseasily; that is, from submicroscopic to symbolic and to macroscopic levels of representation.

Anthropomorphic explanation for the periodic table. In this teaching scenario, theteacher introduced the periodic table and made comments about the elements inthe groups.

Teacher : . . . this is also called a periodic table [Teacher pointing to a periodic tablehanging on the wall]. In the periodic table the horizontal rows are calledperiods and the vertical columns are called groups. The first column is . . .called alkali metals. So the surname of the first group is Alkali, Mr Alkaliand the family name of the second group is Mr Alkali Earth Metals. I

won t go into surnames of all the other families. Groups between II andIII . . . they have schizophrenic chemical behaviour, that is, multiplebehaviours.

Coming to the last column, they come from the house of the lords.Noble gases these elements live in the high society, they do not mix withlow class people like you and me. Let us see why are they such highsociety.

This scenario provides an example of an anthropomorphic explanation thatoccurs when a phenomenon is rendered more familiar by attributing human

characteristics to the nonhuman agent(s) involved (Dagher and Cossman 1992:364). Anthropomorphic explanations have the potential to be misinterpreted ormisunderstood because, in this case, there is a likelihood that some students are notfamiliar with the term schizophrenic and this may result in their inability tounderstand the intended meaning of the representation.

The teacher s explanation was macroscopic and symbolic in nature since itmade use of observable behaviour of chemicals with reference to students everydayexperiences and presented the elements as symbols. The submicroscopic level of representation was presented by the subatomic structure of elements and theirrelationship to the reactivity of the element, thus linking the macroscopic and thesubmicroscopic levels. The aim of the explanation was to demonstrate a relationalunderstanding of the chemical concept of an element s behaviour in relation to itsposition on the periodic table.


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Problem-solving explanation to determine the empirical formulae of an anhydrous salt.In this lesson, the teacher used the results from a laboratory class to illustratehow an empirical formula was derived. He started by briefing students on howhe had prepared his sample of anhydrous barium chloride during the previouslesson.

Teacher : This is how I prepared the sample of anhydrous barium chloride anhydrous means without water [Teacher responding to a question bystudent]. Initially we need to find the weight of the barium chloride beforedrying it [He then wrote on the board as follows].

Water of crystallisation of BaCl 2 XH 2 OMass of dry crucible (empty): = 37.56 gMass of dry crucible + sample = 41.80 gMass of BaCl 2 XH 2 O: = 41.80g 37.56 g

= 4.24 g

At this stage the teacher commented about the BaCl 2 XH 2 O having lost water of crystallization. He continued on the board.

Mass of crucible and dry BaCl 2 = 41.20 gMass of water of crystallisation = 41.80 g 41.20 g

= 0.6gMass of dry BaCl 2 = 4.24g 0.6g

= 3.64 gBaCl 2 H 2 O

Mass ratio 3.64 g 0.6 gMole ratio 3.64/208.20 g 0.6 g/18.016 g

0.0174 0.0333Whole no. 0.0174/0174 0.0333/0174Ratio 1 1.91

1 2Empirical formula BaCl 2 2H 2 O

This explanation based on problem-solving is characterized by a concept or a

phenomenon being explained or clarified during the process of solving a problem oranswering a question. In explaining the problem, students practical experienceswere related to the macroscopic representation, but also there was frequent use of symbolic representations, including chemical symbols, chemical equations, andnumerical data.

The teacher s approach to solving problems of this type with the students in theclassroom appeared to be effective because later, when given additional problems tosolve on their own, students knew exactly what was required. The laboratory workand the associated calculations justified the symbolic formula and served to link themacroscopic and symbolic levels of representation. Students completing similarproblems may only have an instrumental understanding, but when they successfullycompleted problems where some application was required, it is likely that somerelational understanding would be achieved.


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Model-based explanation for atomic structure. In this teaching scenario, about atomicstructure, the teacher explained that:

Teacher : There is not much of mathematics and calculations in this case, but useof diagrams and the following models. [Teacher defined the atom andgave a historical background of its origin] an atom cannot be cut (John

Dalton) . . . it is very abstract . . . Later, people discovered that the atomcan be cut . . . In science, you need to stand your ground as long as youhave evidence and be willing to change your ideas as new evidence arises.Look how it went: John Dalton, Thompson, Rutherford and Niels Bohr.A nucleus is a collection of particles not a bag where you storedsomething. [Teacher drew the diagram on the board] (see figure 3).

The teacher continued to explain the movement of electrons using this model andhe made use of an analogical explanation of a fan s blades to clarify the motion of electrons around the nucleus, to illustrate the Heisenberg s Uncertainty Principle ina simplified form.

Teacher : When the fan is stationery you can identify the number of blades, but asit is turned full blast is it possible to identify each blade? No, it is blurred.Therefore it is the same with electrons, hence the name electron cloud.You cannot identify each and every electron since they are moving at ahigh speed.

Although this model-based explanation concluded with an analogically basedexplanation, its emphasis was more on the elaboration of the various models that areused to represent the structure of an atom. Many symbolic representations providea visual representation of the submicroscopic level. Despite the symbolic repre-sentations being depictions of reality that may not be accurate, they can providetools to help explain features that are not visible. Here the teacher again usedmultiple representations models, analogies, drawings and descriptions to explainthe atomic structure of the atom. The atomic models were presented factually,which most likely led to instrumental understanding since the emphasis was onknowing how rather than knowing why.

Relational explanation for everyday chemical experience. In this lesson, the teacherrelated movement of molecules to students everyday experiences.

Teacher : When you are in a restaurant you can tell from the smell coming from thekitchen that the chef is preparing something nice for you. How are youable to tell?

Figure 3. A diagram of the atom.


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Student : Of course, from the smellTeacher : Can you see smell?Student : No.Teacher : What do you think smell is?Student : Not sure . . . [inaudible]Teacher : Those are molecules, they have travelled from the kitchen into your nose

and yet you did not see them. Do you make sense in what I am saying?Student : Yes, Sir [although he said yes, the student appeared not to be

convinced]

This scenario is an example of a relational explanation referring to the relevanceof an explanation to an explainee. In this type of explanation, a more simplifiedversion of the unfamiliar concept is related to familiar experiences of the learner.The explanation required students to imagine something that they cannot see. Thesubmicroscopic representation of moving molecules, carrying a smell a macro-

scopic quality may prove difficult for students to accept easily. In the previousdiscussion, the teacher expected the students to be able to transfer between the twolevels immediately, thereby intending to engage students in relational under-standing; however, the final comment by the student indicated that this may nothave been successful.

Study 2: Introductory organic chemistry

All the explanations in study 2 can be classified as model-based explanationsbecause the students were required to construct the organic structures of thecompounds they were learning about. At least two symbolic representations wereused for each task: the ball-and-stick model and the written structural formula, withadditional modes included where possible. Four examples of explanations used bythe students are reported.

Model-based explanations for a three-dimensional structure of hydrocarbon. The teacherdescribed models as representations of chemical substances, and students practicedtransferring from the three-dimensional symbolic ball-and-stick representation tothe two-dimensional symbolic structural formula representations. The teacherhighlighted the differences between the two representations being used.

Teacher : It is not always convenient to have your models with you so we draw astructural formula a two-dimensional representation.

Teacher : Obviously an advantage of our model is that it allows us to visualise three-dimensional models. It also allows us to remember that these things haveenergy and that these things are moving all the time twisting, turningvibrating.

Although energy, or the twisting, turning and vibration of the methyl group, cannotbe seen, the teacher was able to effectively use a model that provided an image anda meaning to the explanation to explain the submicroscopic process. The teacher suse of the phrase twisting, turning, vibrating illustrated his attempt to focus on thesubmicroscopic level of representation. However, modelling skills are not inherentin learning or teaching, and the analogical relations of the reality and the model or


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representations need to be established by the student. The teacher appreciated thisand stated:

Teacher : Now it doesn t matter if this methyl group is over here or over there. Youcan imagine because you can flip these around [referring to the structuralformula and the ball-and-stick model] just like you can with your plasticmodels.

Subsequently, the ability to transfer from one symbolic representation to another waspractised in these lessons, with the teacher always reverting to the structural formularepresentations on the board to explain and compare chemical compounds. Studentseventually chose to work without the ball-and-stick model, saying to one another: Just do it on paper, we don t need the model . The symbolic and submicroscopicchemical representations used in this scenario take on a relational form of understanding that helped to forge links between familiar and unfamiliar concepts.

Model-based explanations for the structure and formula of alkanes. In this learningepisode, when students made pentane from models, their conversation with eachother reinforced the number of carbon and hydrogen atoms required and thelengths of the bonds. The explanation of the structure was primarily instrumentallearning in that the students were required to follow specific instructions. In thefollowing dialogue during this activity, students reinforced their understanding of the bonding structure for carbon, the general formula for an alkane and comparedthe symbols for different bonds and different atoms.

Student 2: Yes 1, 2, 3, 4, 5. So far I have five I ve got to connect three morecarbons together

Student 2: It s not going to sit very niceStudent 1: This can be pentane pentane alright?Student 3: HaroldStudent 1: YesStudent 1: Twelve hydrogenStudent 1: 1, 2, 3, 4,. .6, 7, 8, 9 one more, three more . . .Student 2: Three more?Student 1: YeahStudent 1: This isn t pentane. Oh yes it is I didn t count that one

Student 2: What are the green ones?Student 1: Is this pentane?Student 2: Green [ones] are chlorineStudent 1: Andrew, you used the wrong bond on the top.Student 3: That s a better pentaneStudent 1: These bonds are long bonds at the topResearcher : How many carbons?Student 1: Five and twelve hydrogen, pentane?Teacher : Yes that s pentaneStudent 1: For octane we ll just expand it furtherStudent 2: Is it really chlorine? Chlorine!Student 1: Gotcha. This will destroy your lungsStudent 2: Chlorine gas, chlorine gas


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Students repeatedly counted along the ball-and-stick model, identifying thelongest chain. This was invaluable for naming compounds correctly, as in theexample 1, 2, 3, 4, so it s butane, so it s methyl butane . The students dialogue wasindicative that they were confirming and consolidating their nomenclature ruleswith the aid of the ball-and-stick models. The reference to chlorine gas whenreferring to the green balls suggests that students were linking the symbolicrepresentational level to the macroscopic level. Students were able to identify thepattern in the nomenclature and structural formula, suggested by the comment foroctane we will just expand it further . Working in pairs proved to be an effective wayfor students to help and challenge each other. The students explanations of possiblestructural configurations to each other using the models and the diagrams wasindicative of a relational level of understanding. This example supports recom-mendations of Harrison and Treagust (1998: 424) that learning to model should beovertly social and involve discussion and negotiation of meaning .

Model-based explanations for isomeric structures. The following dialogue providesevidence of model-based explanations where the students used the ball-and-stickmodels and the structural formula to help identify alternative and feasible isomersand understand the naming conventions. Students made inferences based on theirobservations of the model. Skemp refers to relational explanations as building up aconceptual structure (schema) from which its possessor can (in principle) producean unlimited number of plans for getting from any starting point within his schemato any finishing point (1976: 25). In this scenario, the students used the ball-and-stick model to explain the differences between isomers and related thesedifferences to other representational forms such as the structural formula. In thisway, the symbolic representations provided explanations that had a relationalunderstanding.

Student 1: Next one, you are going to have two chlorines in the middle. Thatmeans 2, 2 dichloropropane, it is all dichloropropane.

Student 2: This is what we have just done, it is still . . .Student 1: It is all propane and it is dichloropropane and it is just the number and

the fact that the number is 1, 1; 1, 2; 2, 2.Student 2: Perhaps 1,3 . . . What about 1, 3?Student 1: Fine. 2, 2 is here and 1, 2 is just like this.Student 2: 2,3?

Student 1: No it will be 1, 2Student 2: I see. I did not realise you were getting at it. It will be what?Student 1: On what?Student 2: 1, 2; 1, 3Student 1: 1, 2; 1, 3Student 2: and then 2, 2; . . . 1, 2.Student 1: What about 1, 1; 1, 2; 1, 3 and that is it?Student 2: Yeah!

Model-based explanations for identifying cis trans isomers. A second example of dialogue provides evidence of students using these opportunities of working withmodels to reinforce their understanding through a multiple perspective view of themodel often repeating the same idea over and over, getting positive feedback from


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their partner. Students looked for positive reinforcement from their peers and theirteacher, with correct responses building their confidence and understanding. Astudents submicroscopic representation was constructed as a result of theinformation received and interpreted by the student. The use of discussion withpeers and with the teacher helped the students confirm their understanding andacceptance of their representation. Both instrumental and relational understandinglevels of understanding were exhibited. Understanding the meaning of the newterminology of trans and cis forms, applying the naming rules to the newcompounds, and identifying all the possible structures are examples of instrumentalunderstanding. Transferring from the three-dimensional, ball-and-stick model tothe two-dimensional, structural formula, the record in their notes shows a relationallevel of understanding.

Student 1: If we had the CH 3 bond on the same side of the double bond as thechlorine . . .

Student 2: I ve already done that.Student 1: We have . . . atoms.Student 2: I say you put them both on the top, one on the bottom one on the top

and both on the same side trans -chloropropene and then we have cis-chloropropene.

Student 1: Look this one is different.Student 1: There are so many.

The co-operative discussions observed were enriching to both the explainee andthe explainer. The task of explaining their ideas to fellow students revealed theirmisunderstandings and helped clarify their ideas. Students frequently asked theteacher for confirmation, even though they had already discussed an answer withtheir peers, and were confident they were correct. The value of this process isidentified by Horwood, who concluded that the most neglected function of anexplanation is its ability to enable the learner to become an independent explainer (1988: 48).

Conclusions

The data presented from teaching episodes in these two studies have providedexamples of the use of symbolic and submicroscopic representations in explaining

the macroscopic nature of chemical phenomenon from both teacher and studentperspectives. The examples have attempted to show the potential of explanations inexpanding the learners understanding of chemical phenomena. The abstract natureof chemistry and the need for the learner to develop a personal understanding of thesubmicroscopic nature of the chemical nature of matter necessitates the use of anextensive range of symbolic representations such as models, problems andanalogies. Distinguishing the chemical content from the explanatory tools is notalways obvious and, consequently, the role of explanations and the relationship of the symbolic representations to the macroscopic and submicroscopic levels shouldbe overtly discussed.

Two significant pedagogical issues about the role and use of submicroscopicand symbolic representations in understanding chemical explanations and implica-tions for teaching chemistry arise from these teaching episodes.


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1. Effective learning at a relational level of understanding requires simultane-ous use of a variety of both levels of understanding and types of submicroscopic and symbolic representations in chemical explanations.

2. Despite the efforts of the teacher, the role of submicroscopic and symbolicrepresentations may or may not be understood by the learner. Representa-tions are used to help the learner learn; however, the findings from bothstudies showed that students do not always understand the role of therepresentation that is assumed by the teacher.

A significant factor in the students effective use of explanations in these studieswas their ability to recognize the various representational forms of chemicalphenomena and to transfer from one level of chemical representation to another(e.g. submicroscopic to macroscopic, symbolic to submicroscopic). The students conversations in study 2 demonstrated how they gradually became familiar with themode of explanation, learning to use the various representations appropriately and

interpreting their meaning accurately. The variety of explanation types analogical,anthropomorphic, relational, problem-solving and model based were used toexplain chemical phenomena at one or more representational levels. The findingsfrom both studies suggest that familiarity with the purpose of each level of representation can enhance a learner s understanding and ability to explain aconcept. Consequently, the development of students understanding from aninstrumental to a relational level could be aided by linking their experiences of thebehaviour of chemicals at the macroscopic level with the symbolic and submicro-scopic levels of representation.

NoteDr. Livy Thapelo Mamiala is now at the Faculty of Education, Vista University, Port Elizabeth,6000, South Africa.

References

BUXTON , L. (1978). Four levels of understanding. Mathematics in Schools , 17, 36.C OPOLO , C. F. and H OUNSHELL , P. B. (1995). Using three dimensional models to teach molecular

structures in high school chemistry. Journal of Science Education and Technology , 4,295 305.

D AGHER , Z. and C OSSMAN , G. (1992). Verbal explanations given by science teachers: their natureand implications. Journal of Research in Science Teaching , 29, 361 374.

G ABEL , D. (1998). The complexity of chemistry and implications for teaching. In B. J. Fraser andK. G. Tobin (Eds.), International handbook of science education , Vol. 1 (Dordrecht: Kluwer),233 248.

H ARRISON , A. G. and T REAGUST , D. F. (1998). Modelling in science lessons: are there better waysto learn with models? School Science and Mathematics , 98, 420 429.

H ORWOOD , R. H. (1988). Explanation and description in science teaching. Science Education , 72,41 49.

JOHNSTONE , A. H. (1982). Macro- and micro-chemistry. School Science Review , 64, 377 379.K OZMA , R. B. and R USSELL , J. (1997). Multimedia and understanding: expert and novice

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M AMIALA , T. L. and T REAGUST , D. F. (2001). Teachers use of explanations in senior high school chemistry . Paper presented at the Annual meeting of National Association for Research inScience Teaching, St Louis, MO.


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