Niveles de representacion

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The role of submicroscopic and
symbolic representations in chemical
explanations
David Treagust
a
, Gail Chittleborough
a
& Thapelo Mamiala
a
a
Science and Mathematics Education Centre, Curtin University
of Technology, GPO Box U1987, Perth, WA 6845 Australia; e‐mail:
D.Treagust@smec.curtin.edu.au
Published online: 03 Jun 2010.
To cite this article: David Treagust , Gail Chittleborough & Thapelo Mamiala (2003) The role of
submicroscopic and symbolic representations in chemical explanations, International Journal of
Science Education, 25:11, 1353-1368, DOI: 10.1080/0950069032000070306
To link to this article: http://dx.doi.org/10.1080/0950069032000070306
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International Journal of Science Education ISSN 0950–0963 print/ISSN 1464–5289 online © 2003 Taylor & Francis Ltd
http://www.tandf.co.uk/journals
DOI: 10.1080/0950069032000070306
INT. J. SCI. EDUC., NOVEMBER 2003,VOL. 25, NO. 11, 1353–1368
RESEARCH REPORT
The role of submicroscopic and symbolic
representations 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: D.Treagust@smec.curtin.edu.au
Chemistry is commonly portrayed at three different levels of representation – macroscopic, submicroscopic and
symbolic – 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 provide
meaning. 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 lessons
using analogical, anthropomorphic, relational, problem-based, and model-based explanations. Examples of
both teachers’ and students’ dialogue are used to illustrate how submicroscopic and symbolic representations
are manifested in their explanations of observed chemical phenomena. The data in this research indicated that
effective learning at a relational level of understanding requires simultaneous use of submicroscopic and
symbolic 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 is
assumed by the teacher.
Introduction
The effectiveness of school chemistry teaching is dependent on the teacher’s ability
to communicate and explain abstract and complex chemical concepts, and on the
students’ ability to understand the explanations. Expert chemistry teachers present
new information at an appropriate level for the learner, make use of relevant
explanatory artefacts, build on the knowledge and concepts that students already
understand, and provide students with all the information that they need to know
without being beyond their grasp or over-simplifying the content (Treagust and
Harrison 1999). In this article, we examine the use of submicroscopic and symbolic
representations in chemical explanations, and ascertain what they add to explana-
tions and how they provide meaning. The article begins with a discussion of the
three levels of representation in chemistry, an analysis of the types of explanations
used in science classrooms and an examination of different levels of understanding
that are possible with this kind of teaching. This discussion leads to the research
question that guides the research: What is the role of symbolic and submicroscopic
representations on the comprehensibility of chemical phenomenon, and how do
these 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 phenomena
that can include experiences from students’ everyday lives such as colour changes,
observing new products being formed and others disappearing. In order to
communicate about these macroscopic phenomena, chemists commonly use the
symbolic level of representation that includes pictorial, algebraic, physical and
computational forms such as chemical equations, graphs, reaction mechanisms,
analogies and model kits. The submicroscopic level of representation, based on the
particulate theory of matter, is used to explain the macroscopic phenomena in terms
of the movement of particles such as electrons, molecules, and atoms. These
submicroscopic entities are real but they are too small to be observed, so chemists
describe their characteristics and behaviour using symbolic representations to
construct mental images. We contend, as illustrated in figure 1, that all three levels
of representation are integral in developing an understanding of the chemistry
concepts under investigation.
Students’ understanding of the role of each level of representation –
macroscopic, symbolic and submicroscopic – as well as the relationships between
each level is often assumed by chemistry teachers who commonly use all three levels
simultaneously. Furthermore, teachers often assume that students can easily
transfer from one level to another (Johnstone 1982). In comparing the perceptions
of experts and novices on a variety of chemical representations, Kozma and Russell
(1997) concluded that novices used only one form of representation, and rarely
could transform to other forms, whereas the experts transformed easily. Novices
relied on the surface features, for example lines, numbers and colour, to classify the
representations, whereas experts used an underlying and meaningful basis for their
categorization. The study highlighted the need for representational competence,
including an understanding of the features, merits and differences of each form, and
showed 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.

THE ROLE OF REPRESENTATIONS IN CHEMISTRY 1355
transference to be given little consideration, and Johnstone (1982: 379) referred to
the ‘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 submicroscopic
level of representations. Consequently, the ability of students to understand the role
of each level of chemical representation and the ability to transfer from one level to
another is an important aspect of generating understandable explanations. The
simultaneous use of macroscopic, submicroscopic and symbolic representations has
been shown to reduce students’ alternative conceptions in the teaching and learning
of chemical concepts (Russell et al. 1997).
Research studies have shown that it is essential for teachers’ explanations to be
student 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 extensive
range of explanations. For the research in this article, the five most prevalent types
of explanations were analogical, anthropomorphic, relational, problem based, and
model based (see table 1).
Two levels of understanding
Instrumental understanding (knowing how) and relational understanding (knowing
why) are differentiated by the depth of understanding and the application of
knowledge that the learner exhibits (Skemp 1976).The instrumental level reflects a
rote-learning synopsis where the learner knows a rule and is able to use it; on the
other hand, relational understanding reflects meaningful learning in which the
student 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 and
providing immediate rewards and success, whereas relational is more adaptable to
new tasks. The proposed knowledge schema that a student develops at an
instrumental 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 Description
Analogical A familiar phenomenon or experience is used to explain the unfamiliar
Anthropomorphic A phenomenon is given human characteristics to make it more familiar
Relational An explanation that is relevant to the explainees’ personal experience
Problem based An explanation demonstrated through the solving of a problem
Model based Using a scientific model to explain a phenomenon

at a relational level a student’s schema of knowledge would be linked and
interconnected (see figure 2). Skemp emphasized the significance and the subtlety
of the differences between the two types of learning, in that the students may know
the same facts of the subject but their way of knowing is different. This
epistemological perspective draws attention to the importance of foundation
learning being presented in situ as part of a conceptual structure or schema. For
chemistry, the conceptual schema includes the three levels of chemical representa-
tion – macroscopic, submicroscopic and symbolic levels of representation. The
degree of linking between the three levels can provide some insight into the
ontological 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 is
anticipated that the greater linking between the levels of chemical representation
will 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 the
comprehensibility of chemical phenomenon and how do these representations
provide meaning? The two parts of the research question correspond to two levels
of analysis: the description of the impact of particular representations and the
assessment 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 in
co-educational high schools in Perth, Western Australia complement each other in
that they both investigated the use and role of explanations in learning chemistry.
Figure 2. Relationship between levels of understanding and levels of
chemical representation.

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 a
range of academic achievement and whose average age was 16 years. The selection
of 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 in
senior high school.
Study 1: Introductory physical chemistry
The first study involved observations of two chemistry teachers over a 10-week
period 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 molecular
substances 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.The
teachers made use of a variety of explanations, choosing those most appropriate for
the content and format to suit their students’ learning styles.The two teachers, who
each had more than 20 years’ experience in the classroom, were given a broad
outline of the purpose of the study and were encouraged to teach in their normal
style, despite the presence of researchers in the classroom. Both teachers were
interviewed about their choice, justification and delivery of the chemical
explanations.
Study 2: Introductory organic chemistry
The second study involved the implementation of a model-based teaching
programme for introductory organic chemistry including topics on the structures
and properties of alkanes, alkenes, alkynes, cyclo-alkanes, nomenclature, isomer-
ism, and substitution, addition and combustion reactions. This study, with one
chemistry teacher who had over 20 years’ teaching experience, involved observing
24 lessons of two chemistry classes over a 3-week period. The teacher was the head
of science at his school and, during the observed lessons, the teaching approach
involved activities that required the students to build representations of chemical
compounds using ball-and-stick chemical models. With each class, the students
worked in pairs, discussing their answers and recording their results as structural
formula representations
Common methodology for study 1 and study 2
Qualitative data sources for both studies came from classroom observations by two
participant researchers, interviews with teachers and students, and audio-taping
students’ interactions during group work to identify explanatory occurrences that
involved submicroscopic and symbolic representations. The participant researchers
took notes on their observations. In study 1, where possible, both teachers were
interviewed after chemistry lessons and were asked prepared questions about their
choice and delivery of chemical explanations. In study 2, six pairs of students were

randomly selected each lesson to be audio-recorded. In addition, the researchers
questioned students throughout the lessons during group work. The audio
recordings 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 chemistry
topics provided a typical sample of chemical explanations. Both studies provided
examples of submicroscopic and symbolic representations in explanations of
chemical phenomena to address the first part of the research question. The
explanations were examined in terms of their intended level of understanding in
order to respond to the second part of the research question. The types of
explanations in both studies were based on the framework developed by Mamiala
and Treagust (2001) (see table 1).
The authors took on the role of participant observers (Merriam 1998) in order
to document both teachers’ explanations and students’ understanding of these
explanations. 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 observations
with supporting evidence from the interview data.
Results and discussion
Representative examples of the role of submicroscopic and symbolic representations
in chemical explanations have been selected from both studies. The data presented
include the concept to be learnt, the type of explanation used, a portion of the
transcript of the learning situation, an analysis of the teaching event in terms of the
submicroscopic and symbolic representations used, and whether instrumental or
relational 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 a
brief definition of the concept of limiting reagent.
Teacher: A limiting reagent is the one chemical in a reaction that determines how
much of the other chemicals are going to be used up.When you are given
the following reaction:
MgCO3 + 2HCl → MgCl2 + CO2 + H2O
1.70 g 1.46 g
and the amounts reacting are as shown. Which one will you say is a
limiting reagent?
Student: Multiply 1.46 by 2 and divide by the molecular mass . . .
Teacher: Why multiply by 2 . . .?

A student wanted to multiply by 2 because of the numerical coefficient in HCl; the
teacher recognized this issue and introduced an analogy.
Teacher: In a particular community there are 20 male dancers and 20 female
dancers . . . one male is with one female dancer. How many groups will
be 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 female
dancers, 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: the
equation, the numerical values of the amounts of chemical compounds, as well as
the analogy to help the students visualize the concept. Analogies are a common
feature with students’ everyday language and the teachers’ ability to use them
effectively contributes towards students’ understanding of chemical phenomena
(Gabel 1998,Thiele andTreagust 1994). According to Dagher and Cossman (1992:
364), analogical explanations are when ‘a familiar situation similar to the unfamiliar
phenomenon to be explained is used to provide the explanation. A correspondence
is assumed to exist between aspects of the analogical situation and those of the
actual 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 the
annual ball. The ball is one of the most eagerly awaited events in one’s
change of lives, and influences the attitudes, self-esteem, morale and
personality of the kids.
The teacher was asked why it is necessary to use a lot of explanations for some
concepts?
Teacher: For difficult concepts, I use a lot of questioning techniques and a fair bit
of reinforcing techniques. On top of that, the limiting reagent, the excess
reagent, types of products and stoichiometry requires much more
explanation at a ground level. I usually use an analogy and I think it is
going 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 are
dealing with the same boys and girls in different dancing . . . But in
chemical reactions, we are dealing with different chemicals in entirely
different chemical reactions.

In the discussion of limiting reagents, the symbolic representation of the equation
and the analogy helped to develop the submicroscopic representation of the limiting
reagent concept, providing an image of something being left over or, conversely, all
used up. The proposed submicroscopic representation to be understood at the
molecular level is for the molecules to combine and react on a one-to-two ratio.The
classroom observations indicated that the students appeared to follow this type of
explanation with interest. The teacher’s comments indicated that he attributed the
success of the analogy to the meaning that the analogy had for these particular
students. The teacher was aware of the difficulty of the concept and used multiple
strategies to reinforce the concept.When students can apply the concept of limiting
reagents 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 chemicals
easily; that is, from submicroscopic to symbolic and to macroscopic levels of
representation.
Anthropomorphic explanation for the periodic table. In this teaching scenario, the
teacher introduced the periodic table and made comments about the elements in
the groups.
Teacher: . . . this is also called a periodic table [Teacher pointing to a periodic table
hanging on the wall]. In the periodic table the horizontal rows are called
periods and the vertical columns are called groups.The first column is . . .
called alkali metals. So the surname of the first group is Alkali, Mr Alkali
and 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 and
III . . . they have schizophrenic chemical behaviour, that is, multiple
behaviours.
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 with
low class people like you and me. Let us see why are they such high
society.
This scenario provides an example of an anthropomorphic explanation that
occurs 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 or
misunderstood because, in this case, there is a likelihood that some students are not
familiar with the term schizophrenic and this may result in their inability to
understand the intended meaning of the representation.
The teacher’s explanation was macroscopic and symbolic in nature since it
made use of observable behaviour of chemicals with reference to students’ everyday
experiences and presented the elements as symbols. The submicroscopic level of
representation was presented by the subatomic structure of elements and their
relationship to the reactivity of the element, thus linking the macroscopic and the
submicroscopic levels. The aim of the explanation was to demonstrate a relational
understanding of the chemical concept of an element’s behaviour in relation to its
position on the periodic table.

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 illustrate
how an empirical formula was derived. He started by briefing students on how
he had prepared his sample of anhydrous barium chloride during the previous
lesson.
Teacher: This is how I prepared the sample of anhydrous barium chloride –
anhydrous means without water [Teacher responding to a question by
student]. Initially we need to find the weight of the barium chloride before
drying it’ [He then wrote on the board as follows].
Water of crystallisation of BaCl2XH2O
Mass of dry crucible (empty): = 37.56 g
Mass of dry crucible + sample = 41.80 g
Mass of BaCl2XH2O: = 41.80g–37.56 g
= 4.24 g
At this stage the teacher commented about the BaCl2XH2O having lost water of
crystallization. He continued on the board.
Mass of crucible and dry BaCl2 = 41.20 g
Mass of water of crystallisation = 41.80 g–41.20 g
= 0.6g
Mass of dry BaCl2 = 4.24g–0.6 g
= 3.64 g
BaCl2 H2O
Mass ratio 3.64 g 0.6 g
Mole ratio 3.64/208.20 g 0.6 g/18.016 g
0.0174 0.0333
Whole no. 0.0174/0174 0.0333/0174
Ratio 1 1.91
1 2
Empirical formula BaCl2·2H2O
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 or
answering a question. In explaining the problem, students’ practical experiences
were related to the macroscopic representation, but also there was frequent use of
symbolic representations, including chemical symbols, chemical equations, and
numerical data.
The teacher’s approach to solving problems of this type with the students in the
classroom appeared to be effective because later, when given additional problems to
solve on their own, students knew exactly what was required. The laboratory work
and the associated calculations justified the symbolic formula and served to link the
macroscopic and symbolic levels of representation. Students completing similar
problems may only have an instrumental understanding, but when they successfully
completed problems where some application was required, it is likely that some
relational understanding would be achieved.

Model-based explanation for atomic structure. In this teaching scenario, about atomic
structure, the teacher explained that:
Teacher: There is not much of mathematics and calculations in this case, but use
of diagrams and the following models. [Teacher defined the atom and
gave a historical background of its origin] an atom cannot be cut (John
Dalton) . . . it is very abstract . . . Later, people discovered that the atom
can be cut . . . In science, you need to stand your ground as long as you
have 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 stored
something. [Teacher drew the diagram on the board] (see figure 3).
The teacher continued to explain the movement of electrons using this model and
he 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 in
a simplified form.
Teacher: When the fan is stationery you can identify the number of blades, but as
it 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 a
high speed.
Although this model-based explanation concluded with an analogically based
explanation, its emphasis was more on the elaboration of the various models that are
used to represent the structure of an atom. Many symbolic representations provide
a visual representation of the submicroscopic level. Despite the symbolic repre-
sentations being depictions of reality that may not be accurate, they can provide
tools to help explain features that are not visible. Here the teacher again used
multiple representations – models, analogies, drawings and descriptions – to explain
the atomic structure of the atom. The atomic models were presented factually,
which most likely led to instrumental understanding since the emphasis was on
knowing how rather than knowing why.
Relational explanation for everyday chemical experience. In this lesson, the teacher
related movement of molecules to students’ everyday experiences.
Teacher: When you are in a restaurant you can tell from the smell coming from the
kitchen that the chef is preparing something nice for you. How are you
able to tell?
Figure 3. A diagram of the atom.

Student: Of course, from the smell
Teacher: 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 relevance
of an explanation to an explainee. In this type of explanation, a more simplified
version of the unfamiliar concept is related to familiar experiences of the learner.
The explanation required students to imagine something that they cannot see. The
submicroscopic representation of moving molecules, carrying a smell – a macro-
scopic quality – may prove difficult for students to accept easily. In the previous
discussion, the teacher expected the students to be able to transfer between the two
levels immediately, thereby intending to engage students in relational under-
standing; however, the final comment by the student indicated that this may not
have been successful.
Study 2: Introductory organic chemistry
All the explanations in study 2 can be classified as model-based explanations
because the students were required to construct the organic structures of the
compounds they were learning about. At least two symbolic representations were
used for each task: the ball-and-stick model and the written structural formula, with
additional modes included where possible. Four examples of explanations used by
the students are reported.
Model-based explanations for a three-dimensional structure of hydrocarbon. The teacher
described models as representations of chemical substances, and students practiced
transferring from the three-dimensional symbolic ball-and-stick representation to
the two-dimensional symbolic structural formula representations. The teacher
highlighted the differences between the two representations being used.
Teacher: It is not always convenient to have your models with you so we draw a
structural 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 have
energy and that these things are moving all the time twisting, turning
vibrating.
Although energy, or the twisting, turning and vibration of the methyl group, cannot
be seen, the teacher was able to effectively use a model that provided an image and
a meaning to the explanation to explain the submicroscopic process. The teacher’s
use of the phrase ‘twisting, turning, vibrating’ illustrated his attempt to focus on the
submicroscopic level of representation. However, modelling skills are not inherent
in learning or teaching, and the analogical relations of the reality and the model or

representations need to be established by the student. The teacher appreciated this
and stated:
Teacher: Now it doesn’t matter if this methyl group is over here or over there.You
can imagine because you can flip these around [referring to the structural
formula and the ball-and-stick model] just like you can with your plastic
models.
Subsequently, the ability to transfer from one symbolic representation to another was
practised in these lessons, with the teacher always reverting to the structural formula
representations on the board to explain and compare chemical compounds. Students
eventually 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 submicroscopic
chemical 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 learning
episode, when students made pentane from models, their conversation with each
other reinforced the number of carbon and hydrogen atoms required and the
lengths of the bonds. The explanation of the structure was primarily instrumental
learning in that the students were required to follow specific instructions. In the
following dialogue during this activity, students reinforced their understanding of
the bonding structure for carbon, the general formula for an alkane and compared
the 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 more
carbons together
Student 2: It’s not going to sit very nice
Student 1: This can be pentane – pentane alright?
Student 3: Harold
Student 1: Yes
Student 1: Twelve hydrogen
Student 1: 1, 2, 3, 4,. .6, 7, 8, 9 – one more, three more . . .
Student 2: Three more?
Student 1: Yeah
Student 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 chlorine
Student 1: Andrew, you used the wrong bond on the top.
Student 3: That’s a better pentane
Student 1: These bonds are long bonds at the top
Researcher: How many carbons?
Student 1: Five and twelve hydrogen, pentane?
Teacher: Yes that’s pentane
Student 1: For octane we’ll just expand it further
Student 2: Is it really chlorine? Chlorine!
Student 1: Gotcha. This will destroy your lungs
Student 2: Chlorine gas, chlorine gas

Students repeatedly counted along the ball-and-stick model, identifying the
longest chain. This was invaluable for naming compounds correctly, as in the
example ‘1, 2, 3, 4, so it’s butane, so it’s methyl butane’.The students’ dialogue was
indicative that they were confirming and consolidating their nomenclature rules
with the aid of the ball-and-stick models. The reference to chlorine gas when
referring to the green balls suggests that students were linking the symbolic
representational level to the macroscopic level. Students were able to identify the
pattern in the nomenclature and structural formula, suggested by the comment ‘for
octane we will just expand it further’.Working in pairs proved to be an effective way
for students to help and challenge each other.The students’ explanations of possible
structural configurations to each other using the models and the diagrams was
indicative of a relational level of understanding. This example supports recom-
mendations of Harrison andTreagust (1998: 424) that ‘learning to model should be
overtly social and involve discussion and negotiation of meaning’.
Model-based explanations for isomeric structures. The following dialogue provides
evidence of model-based explanations where the students used the ball-and-stick
models and the structural formula to help identify alternative and feasible isomers
and understand the naming conventions. Students made inferences based on their
observations of the model. Skemp refers to relational explanations as ‘building up a
conceptual structure (schema) from which its possessor can (in principle) produce
an unlimited number of plans for getting from any starting point within his schema
to any finishing point’ (1976: 25). In this scenario, the students used the ball-
and-stick model to explain the differences between isomers and related these
differences to other representational forms such as the structural formula. In this
way, the symbolic representations provided explanations that had a relational
understanding.
Student 1: Next one, you are going to have two chlorines in the middle. That
means 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, 2
Student 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, 3
Student 1: 1, 2; 1, 3
Student 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 with
models to reinforce their understanding through a multiple perspective view of the
model – often repeating the same idea over and over, getting positive feedback from

their partner. Students looked for positive reinforcement from their peers and their
teacher, with correct responses building their confidence and understanding. A
students’ submicroscopic representation was constructed as a result of the
information received and interpreted by the student. The use of discussion with
peers and with the teacher helped the students confirm their understanding and
acceptance of their representation. Both instrumental and relational understanding
levels of understanding were exhibited. Understanding the meaning of the new
terminology of trans and cis forms, applying the naming rules to the new
compounds, and identifying all the possible structures are examples of instrumental
understanding. Transferring from the three-dimensional, ball-and-stick model to
the two-dimensional, structural formula, the record in their notes shows a relational
level of understanding.
Student 1: If we had the CH3 bond on the same side of the double bond as the
chlorine . . .
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 and
the explainer. The task of explaining their ideas to fellow students revealed their
misunderstandings and helped clarify their ideas. Students frequently asked the
teacher for confirmation, even though they had already discussed an answer with
their peers, and were confident they were correct. The value of this process is
identified by Horwood, who concluded that the most neglected function of an
explanation 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 provided
examples of the use of symbolic and submicroscopic representations in explaining
the macroscopic nature of chemical phenomenon from both teacher and student
perspectives. The examples have attempted to show the potential of explanations in
expanding the learners’ understanding of chemical phenomena.The abstract nature
of chemistry and the need for the learner to develop a personal understanding of the
submicroscopic nature of the chemical nature of matter necessitates the use of an
extensive range of symbolic representations such as models, problems and
analogies. Distinguishing the chemical content from the explanatory tools is not
always obvious and, consequently, the role of explanations and the relationship of
the symbolic representations to the macroscopic and submicroscopic levels should
be overtly discussed.
Two significant pedagogical issues about the role and use of submicroscopic
and symbolic representations in understanding chemical explanations and implica-
tions for teaching chemistry arise from these teaching episodes.

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 symbolic
representations may or may not be understood by the learner. Representa-
tions are used to help the learner learn; however, the findings from both
studies showed that students do not always understand the role of the
representation that is assumed by the teacher.
A significant factor in the students’ effective use of explanations in these studies
was their ability to recognize the various representational forms of chemical
phenomena 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 the
mode 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 to
explain chemical phenomena at one or more representational levels. The findings
from both studies suggest that familiarity with the purpose of each level of
representation can enhance a learner’s understanding and ability to explain a
concept. Consequently, the development of students’ understanding from an
instrumental to a relational level could be aided by linking their experiences of the
behaviour of chemicals at the macroscopic level with the symbolic and submicro-
scopic levels of representation.
Note
Dr. 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.
COPOLO, C. F. and HOUNSHELL, P. B. (1995). Using three dimensional models to teach molecular
structures in high school chemistry. Journal of Science Education and Technology, 4,
295–305.
DAGHER, Z. and COSSMAN, G. (1992). Verbal explanations given by science teachers: their nature
and implications. Journal of Research in Science Teaching, 29, 361–374.
GABEL, D. (1998). The complexity of chemistry and implications for teaching. In B. J. Fraser and
K. G. Tobin (Eds.), International handbook of science education, Vol. 1 (Dordrecht: Kluwer),
233–248.
HARRISON, A. G. and TREAGUST, D. F. (1998). Modelling in science lessons: are there better ways
to learn with models? School Science and Mathematics, 98, 420–429.
HORWOOD, 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.
KOZMA, R. B. and RUSSELL, J. (1997). Multimedia and understanding: expert and novice
responses to different representations of chemical phenomena. Journal of Research in Science
Teaching, 34, 949–968.
MAMIALA, T. L. and TREAGUST, D. F. (2001). Teachers’ use of explanations in senior high school
chemistry. Paper presented at the Annual meeting of National Association for Research in
Science Teaching, St Louis, MO.

1368 THE ROLE OF REPRESENTATIONS IN CHEMISTRY
MERRIAM, S. B. (1998). Qualitative research and case study applications in education (San Francisco,
CA: Jossey-Bass).
RUSSELL, J. W., KOZMA, R. B., JONES, T., WYKOFF, J., MARX, N. and DAVIS, J. (1997). Use of
simultaneous-synchronised macroscopic, microscopic and symbolic representations to
enhance the teaching and learning of chemical concepts. Journal of Chemical Education, 74,
330–334.
SKEMP, R. R. (1976). Relational understanding and instrumental understanding. Mathematics
Teaching, 77, 20–26.
TREAGUST, D. F. and HARRISON, A. G. (1999). The genesis of effective scientific explanations for
the classroom. In J. Loughran (Ed.), Researching teaching: methodologies and practices for
understanding pedagogy (London: Falmer), 28–43.
THIELE, R. B. and TREAGUST, D. F. (1994). An interpretive examination of high school chemistry
teachers’ analogical explanations. Journal of Research in Science Teaching, 31, 227–242.

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