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Student conceptions of chemical bonding: using

interviews to follow the development of A level

students’ thinking.

Keith S. Taber

(then at Havering College of Further & Higher Education & Roehampton Institute London)

paper presented to the

Conference on On-going Research

Facets of Education - Dimensions of ResearchJune 1993,

Institute of Educational Research and Development, University of Surrey.

Correspondence:

Dr. Keith Taber, Homerton College, University of Cambridge, CB2 2PH

e-mail: [email protected] & [email protected]

Taber K S 1993 - Student conceptions of chemical bonding…

Student conceptions of chemical bonding: using interviews to follow the development of A level students’ thinking.

Keith S. TaberHomerton College, University of Cambridge

Abstract: In recent years there has been a considerable amount of research activity into student conceptions in a variety of areas of science. Chemical bonding is a key concept area for students of A level chemistry, and one which has not received as much attention as its importance might suggest. It is a topic which can be taught, and understood, at a variety of levels of sophistication. At Advanced level an appropriate understanding of bonding will relate to the concepts of force and energy - ideas not usually explicitly explored in their own right in a chemistry course.

The present study aims to explore not only the extent and nuances of student conceptions of chemical bonding, but also the development of these ideas during the students’ course. During the pilot study subjects were interviewed at three stages in their A level course: after one term, at the end of the first year, and just before the final examination.

Data will be presented to illustrate some aspects of the thinking that subjects exhibited, and in particular to demonstrate both how understanding can become more sophisticated over time, and how conceptions in conflict with the accepted wisdom can be tenacious once acquired.

There will also be a short discussion of the development of methodology being undertaken for this enquiry.

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Introduction.

The on-going research I wish to discuss today concerns the development of student understanding in a particular area of science. As such it might be seen to fall within a field of educational enquiry that has become very popular in the past decade or so 1. This research looks at the conceptions or constructs that learners have in certain topic areas, and rather than dismiss those that are not consistent with the teacher’s conceptions, it attaches great importance to these ideas. This interest is based both on pedagogic and more fundamental philosophical concerns. At a practical level new learning is not considered to be independent of current understanding, and therefore constructivist teaching schemes aim to uncover and (where necessary) challenge existing conceptions 2 .

In addition there is a view that children’s science should be afforded respect, and should not be dismissed as invalid because it does not match the accepted scientific wisdom. These perspectives are related to modern views of the nature of science and the way people learn 3. Much of the current work into children’s conceptions is based on Kelly’s metaphor of people-as-scientists (Watts & Pope, 1989; Pope & Watts, 1988; Swift et al., 1983) 4 which considers learners as constructing meaning through internal models of the world which are informed by their experiences, and modified in the light of empirical evidence. The constructivist school wishes to develop teaching schemes to build on children’s science, not devalue it (Scott, 1987).

1 In 1983 two related papers reviewing work into children’s science were published side-by-side in Studies in Science Education (“Theories-in-action: some theoretical and empirical issues in the study of students’ conceptual frameworks in science” (Driver & Erickson, 1983), and “Concepts, misconceptions and alternative conceptions: changing perspectives in science education” (Gilbert & Watts, 1983)). Perhaps the simultaneous publication of two important review articles in this area suggests a field of science education research had ‘come of age’. In the decade since this time there has continued to be an ongoing plethora of publications looking at what have variously been called students’ misconceptions, theories-in-action, alternative conceptions, or intuitive theories (e.g. Pope & Denicolo, 1986), in a variety of areas of science (for a bibliography, see Carmichael, et al, 1990-2.)

2 Such as the materials produced by the Children’s Learning in Science Project, e.g. Wightman, 1986. Alternatively if early formal teaching uses bridging models, metaphors or analogies that are intended to be useful steps to eventual more sophisticated understanding, but in practice have such intrinsic appeal that they interfere with subsequent learning, then new teaching schemes may be suggested that avoid the use of such models (e.g. Jiménez-Aleixandre, 1992).

3 With respect to science, the work of Kuhn (1970) and his contemporaries makes all scientific knowledge somewhat relativist and culturally determined, so that we can no longer dismiss students’ ideas as being simply ‘wrong’ and our own (i.e. teachers etc.) views as right. Indeed since the widespread acceptance of Popper’s analysis of the logic of scientific discovery (1959), the scientific community has had to be content with knowledge that has temporary status: theories that are little more than conjectures awaiting refutation. If all the science we teach is subject to falsification, its difference in status to students’ alternative conceptions is no more than one of degree. Some might argue that is is unfair to compare the, maybe fanciful, ideas of a young child with the consensus, peer-reviewed, critically established results of centuries of scientific investigation.

4 It could be asked what type of scientist? - i.e. which philosophical model of science is most appropriate as a metaphor for young learners? Watts and Pope (1982) have asked this question, and explored the hypothesis that Lakatos’ model is the most suitable.

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Why study learners’ ideas of chemical bonding?

Although a large amount of work has been undertaken into children’s science, it has not been evenly spread across the science curriculum, and few studies seem to have looked at chemical bonding (e.g. Peterson, et al, 1986; Zoller, 1990.) This is surely not related to the importance of the topic. Bonding is one of the more central concepts in any chemistry course, and becomes more important at higher levels where one tries to build up a systematic theoretical basis for the subject. Atomic structure and chemical bonding are among the key ideas in understanding (rather than just describing) chemistry. 5

5 I would suggest several reasons why this topic has not yet been afforded the attention it deserves:-a) Chemical bonding is a topic that is usually only met by students relatively late in their schooling, whereas energy - for example - is often discussed quite early in their formal education.b) Even quite young children often have some ideas related to motion, stars, plant nutrition, light, etc., as these are all phenomena they have direct experience of, whereas the arrangement of sub-microscopic hypothetical particles is not something that they would be expected to have formed ideas about! I am investigating the understanding of very abstract concepts.c) Chemical bonding is understood by scientists themselves through a large variety of models, of various degrees of abstraction and applicability, and of increasing sophistication as one learns chemistry at successively higher levels (Taber, 1993a.) There is no simple benchmark against which to measure student ideas, such as Newton’s first and second laws of motion in mechanics.d) When chemical bonding is taught during the secondary stage of education (i.e. KS4) the level of explanation has tended to be limited, and perhaps investigators have not been too sure what they want students to understand (rather than recall) about the topic? {For example, an explanation (paraphrased) from one book (Gilmore, 1978) at this level: A group of elements are unreactive. They mostly have 8 electrons in their outer shells, except for the one that has 2 electrons in its outer shell. Therefore these electronic configurations are stable. (Why?) “It should come as no great surprise, therefore, that all elements try to achieve the noble gas electronic configuration when they combine. Different ways of achieving the noble gas electronic structure lead to different types of bond.” (p.29.) Another book explains bonding thus: “The elements which have an outside shell containing a maximum number of electrons are very unreactive. ... They do not react because they have no reason to do so. Their outside shell of electrons is full. All the other elements are reactive because they have incomplete outside shells. In reacting they are aiming to have full outside shells.” (Hart, 1978, p.62. Emphasis mine.) Of course, accepting the use of the ‘shell’ notation, only two of the noble gases actually have the maximum number of electrons: helium (2), and neon (8): argon is 10 deficient, and krypton 24 ‘short’! But as long as you define the maximum number of electrons in the outside shell as being the number in the noble gas case, then it is quite correct to suggest “The elements which have an outside shell containing a maximum number of electrons are very unreactive...” Do I detect a slight tautology here?}e) Any deep understanding of bonding is based on more fundamental ideas: energy, force, particle theory (and at a higher level quantum mechanics) - areas where researchers are still busy studying student conceptions. Perhaps researchers have felt that chemical bonding is an area best left alone until more is known about how students understand these supporting concepts! As a teacher of physics I am well aware of some of the difficulties students have in these supporting areas, but as a teacher of chemistry I am also aware of the extent to which chemical bonding concepts permeate my A level chemistry teaching, and therefore it is important for me to investigate this topic area. Indeed to some extent, the aspects of this topic that make it problematic also make it fascinating.

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The longitudinal nature of the research.

Although a young child may have no intuitive ideas about chemical bonding, a sixteen year old starting an A level chemistry course will have received some instruction in this subject, and will have tried to make sense of this teaching in terms of any existing knowledge that was seen to be relevant. A student who made no such links could learn the material as a pure abstraction, maybe an intellectual game akin to chess or the glass bead game 6, where the model is learnt for its own sake, or for passing a test. Any meaning it has is in its own terms. In view of the level of abstraction from everyday experience it is quite possible that some students’ understanding of bonding is indeed in such terms! However those pupils who are able to forge links with their understanding of chemical changes, electrostatic attraction, chemical reactivity, conductivity, the states of matter and so forth may well import their alternative conceptions from these areas into their developing ideas of bonding. In addition if their teachers refer to terms such as ‘charge’, ‘force’, ‘attraction’, ‘repulsion’, ‘electrical’, ‘electrostatic’, and/or ‘energy’ when they are explaining bonding, and if such a connection seems relevant enough to the learner for her to make sense of the link, then the concept constructed by the student will be associated with any alternative frameworks that she has for these terms. So I am very interested in what students understand about chemical bonding at the start of their A level course. If one is building upon existing foundations it is important to know what those foundations are. So my starting point is to try and uncover relevant student understandings before any formal A level teaching of bonding takes place.

Chemists are concerned to explain the physical and chemical properties of substances in terms of a theoretical model. The chemical bonding model used at 16+ is insufficient for this purpose, except for a small range of observable properties. To explain, for example, why water freezes at 0°C, but nitrogen only at -210°C, it is not very helpful to be told that they both have a type of bonding called covalent. Copper chloride and table salt (sodium chloride) both have a type of bonding called ionic, but one is coloured and the other isn’t. Silver and sodium both have a type of bonding called metallic, but sodium can easily be cut with an ordinary knife, unlike silver; and whereas silver is resistant to tarnishing, sodium reacts rapidly with air. Silver does not melt until it is heated to a temperature of 960°C, whereas sodium would melt if placed in boiling water - except that (unlike silver) it would actually react with the water quite explosively before it was able to melt! In order to explain all of these, and many other, properties the student’s model of chemical bonds needs to be considerably extended. So having found out what the students know and understand when they set out on their A levels, I am then interested in following their developing ideas throughout the course.

6 The novelist Hermann Hesse’s vision of an ultimate abstract academic and intellectual activity.

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The research project.

The first pilot stage of the enquiry involved tape-recorded interviews with four volunteer A level students (whom with great imaginative flourish I have signified A - D) at three stages of their course: after one term, after one year, and just before their final examinations. The interviews were semi-structured, with a series of 17 diagrams of the type used in chemistry courses as the foci 7. Other students have since been interviewed, and at present a cohort of eight first year A level students 8 are involved in the study. Data has also been collected by other techniques, as is discussed later.

Some early results from the research.

The research interviews carried out so far have proved themselves to be very fruitful in revealing aspects of student talk and thought 9. Analysis of much of the data is still at a preliminary stage, and with the present audience having varying interests and backgrounds this is not the place for in-depth discussions of the subtleties of chemical theory. Instead I wish to offer a selection of tasters of the kind of insights that this method allows. I hope that you will forgive the somewhat cavalier and cursory nature of this review, in view of the limited time allocated for presentations in this forum. I intend to make available more detailed discussion of much of this material at a later date.

Alternative conceptions.

Whilst student statements that are consistent with the teacher-researcher’s own conceptions of the topic area are certainly of interest, it is those utterances which are contradictory to the accepted model which are often given most attention in research of this type.

One alternative conception uncovered is the identification of the properties of an element, with the properties of a compound of that element. For example subject C 10 suggested that

7 Some data from the first year of this pilot has previously been reported (Taber, 1991).8 denoted J, K, L, N, P, Q, T & U.9 Language and thinking are of course very closely related, but it should be borne in mind that what is

collected directly is student talk (and then in a very specific clinical setting), from which aspects of thinking are induced.

10 brief details of the subjects referred to is appended (as appendix D.)

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potassium chloride might be ‘clear’ because “the chlorine bleaches it” (C2.301 11). This shows ignorance of a basic principle that the properties of compounds are often quite distinct from the properties of the component elements. For example anyone trying to eat sodium would badly burn their mouth, and inhalation of chlorine would lead to the “froth-corrupted lungs” 12 described in the war poem, but it is common to sprinkle sodium chloride, salt, on food without any ill effects! Indeed the very lack of reactivity of this compound is related to the high reactivity of the elements from which it is composed. Again C feels that potassium sulphate, another compound of a reactive metal, will be reactive (C2.371) whereas in fact it too is a stable 13 substance. This is not an isolated example of this conception. Even though my methodology involves in-depth interviews with a small number of subjects (rather than survey-type interviews with statistically significant samples) I have already uncovered several other examples of students misapplying the reactivity of an element to its compounds. Subject J reported that lithium fluoride would be unstable as fluorine is reactive (J2-B219 14), and subject T thought that potassium fluoride would be quite reactive (T2-A503).

Subject T also demonstrated a view that an object in motion is imparted force (T2-B223), and that force was a conserved property, in the sense that a nucleus with a specific positive charge is limited to attracting a given number of negative charges (T7-A565) - i.e. this subject considered electronic shielding as the positive nuclear charge being ‘used up’ on core electrons, rather than being partially balanced by the effects of their charge 15 . Such a misconception is potentially tenacious as it will lead the student to correct hypotheses in some situations, and will tend to be reinforced by giving the ‘right answers’ in these cases. 16

11 for completeness I will cite the data used to base my comments. This quotation is taken from utterance 27 of the transcript of the first interview with A (interview A1). Information on the way in which comments are related to the original data base is given in Taber, 1993b.

12 Dulce et Decorum Est, Wilfred Owen13 stability is of course a relative term. 14 for interviews that have not been fully transcribed, detailed notes have been made. In these cases the

citation refers to the approximate location on the cassette tape recording. E.g.: J2-B219, second interview with J, side B of cassette, tape counter number 219 (see Taber, 1993b.)

15 Most recent work has uncovered another example of a student with this view.16 Another, example of an alternative understanding of forces was uncovered when discussing the nucleus

(see appendix B.) Most atomic nuclei contain several positively charged particles that should repel each other according to basic electrostatic principles. The atomic nucleus is however held together by forces that are quite different, and at close range much stronger, than these electrical forces. Subject A however suggests the nucleons are held together by “forces from the outer ring [of electrons]”, “electronic forces” (A1.27) which are “pushing them” (A1.29) . As it is most unlikely that A would have formally been taught about nuclear forces in any depth, it is not surprising that she is unclear about their nature. However her suggestion is most illuminating as an application of electrostatic ideas: ideas which underpin much chemical theory at this level. Her suggestion has two basic flaws: firstly that the repulsion between adjacent protons could be cancelled by forces from more distant charges of similar magnitude - i.e. she ignores the dependence of such forces on the separation of the charges. Secondly she considers that the negative electrons will repel the positive nucleus, (although in answer to a subsequent question (A1.43) A shows she is aware of an attractive force acting on the electrons due to the nucleus.)

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Of the three main models of chemical bonding likely to be met prior to an A level course students studied so far seem to generally have a good understanding of the basic covalent model, little knowledge of bonding in metals, and often serious misconceptions about ionic bonding. (Some further details are given in appendix A.)

Examples of the development of student understanding during the course.

An example of the development of student conceptions may be found in subject B’s understanding of the ionic bond. Like several other students B referred to the inappropriate construct “sodium chloride molecule” (B1.242) when shown my focus figure 5 (appendix C). Later during the year B was asked if there were any molecules in the figure, and he agreed that there were (B2.26). He thought there were “numerous” (B2.30) molecules shown, and indicated that individual sodiums and chlorines could be part of several molecules at the same time (B2.40). However a year later B reported that the same diagram did not show any molecules (B3.70), only ions (B3.74).

In a similar way it was possible to see how B’s knowledge of metallic bonding developed during the course. During the first interview he reported that focus figure 6 (appendix C) represented “metallic bonding” (B1.286), although he was unable to offer any suggestions as to what this was. By the next interview B was able to describe a “sea of delocalised electrons, and the attractions between the cations, the metallic cations, and the electrons” (B2.42) holding the structure together.

Another example concerns subject C’s understanding of metallic bonding. On being shown focus figure 6 she described it as representing “a lump of iron” (C1.296). She felt there had to be bonds present “or it wouldn’t be held together” (C1.298), but suggested these bonds might be covalent (C1.300), and after some discussion decided that there was no set number of bonds that a particular iron atom would have (C1.332). However a few months later C described the same diagram as “metallic bonding, because it’s a solid, a close-packed solid, and it’s iron, it’s a metal.” (C2.259) “Which means it’s got delocalised electrons, like a sea, which they can move about.” (C2.261) The structure was held together by the attraction between the “the iron ions {laughs.} And the electrons.” (C2.263) It is pleasing to note an example where some effective learning (and possibly even effective teaching) has taken place!

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The tenacity of student alternative conceptions.

An example of a tenacious alternative construct is subject A’s conception of ionic bonding. During the first interview it became clear that A did not understand what was intended by the ‘+’ and ‘-’ signs used to signify charged species that have donated or accepted electrons. A had constructed an alternative meaning: for her the ‘+’ represented a species which had one electron in it’s outermost shell which it would tend to donate to achieve a stable electronic structure, and likewise the ‘-’ implied one electron short of such a structure. Despite formal teaching of ionic bonding, A retained her original framework for making sense of these symbols, and even developed complex, but consistent, arguments about how to form neutral species from combinations of such signs. This alternative framework was still being applied a few weeks before the final examination and some last minute remedial teaching was entered into. (Further details of this example are appended in appendix A.)

Response style.

Different students display different styles of talk in the interviews. Extended interviews allow the researcher to recognise such styles, and avoid reading into specific responses what are no more than general characteristics of speech. Subject A often seemed very unsure of herself, liberally sprinkling “sort of”s and “like”s throughout her talk, as well as justifying statements as “obvious”:

“The electrons are held in, erm, in sort of levels, so, it’s to do with sort of bonding, like you can only get two electrons in the first quantum shell. So that they are held in these shells. Why they don’t quite fall into the nucleus, I’m not quite sure, but obviously you are going to get sort of very minute particles, of the element, which is going to sort of stop them. Again you can’t really say, you’ve got a slab of, sort of, say, erm, sodium or something, you can’t really say, right in the middle of there, there’s the nucleus, because sort of, or, of them if you gave me like a block of sulphur, or sodium sorry, and you sort of put a pin into half the middle, you couldn’t say right that’s the nucleus because it’s sort of held all together, because it’s made up of atoms, although you assume the nucleus is in the centre because that’s the obvious place to be, so obviously it’s going to be in the centre, so it gets sort of the elec.., erm the sort of forces are distributed evenly around, its er, you can’t, you couldn’t detect it in a classroom, well you could with erm, goodness all these gadgets they have these days. Er, so, they’re they’re all held in quantum shells which are different energy levels, and you can sort of promote electrons should you need to in bonding, so, so if for example you need a bond to have, I don’t know, an extra electron in a p orbital, you can donate an s, s electron across, to give you hybrids, things. But why

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they fall into the nucleus {sic} I’m, not quite sure. I don’t think I could describe that.” (A3.10, emphasis added.)

Subject B in contrast spoke very confidently about familiar ideas, but was not prepared to speculate in unfamiliar areas. Subject C had a completely different style of response, one that I have somewhat flippantly labelled as the ‘random thought generator’. She would rapidly suggest ideas, agree with herself, contradict herself, disagree with herself, decide she was talking nonsense, and suggest something else. Each ion could form one bond, no seven, no, an unlimited number (C1.262); the angle was 102°, or 107°, or 117° (C1.591); electrons are localised, but able to move (C1.609); lengths are the same, or different, but not necessarily different (C1.772). C gave some insight into her metacognitive processes, with such comments on her own responses as

“I don’t know what that’s got to do with it though” (C1.433),“what I’ve just said, I don’t agree with” (C1.372),“but that don’t make sense really” (C1.563),

and the interesting insight: “I nearly said the right answer” (C1.752)

Natural states.

One interesting finding concerns what might be classed as ‘natural’ states - those situations that the subject does not feel the need to explain as they are ‘natural’ 17. For example N appeared to have a different intuitive understanding of inter-atomic forces than T. Whereas N recognised that the particles in metals cohere, and there should be a cause of this, T seemed to see cohesion as a natural state which did not need further explanation. T suggested the particles in a solid would not fall apart as they did not have a lot of energy (T1-B509). T felt that there was a force between the molecules in a solid, but that he did not need to suggest any cause of this, it was a result of them not having the energy to “break away to be by themselves” (T1-C165). It is interesting that these two students should appear to assume different natural states, such that one felt it appropriate to suggest a mechanism why molecules should sometimes stick together, whereas the other though this inappropriate, but felt it necessary to explain how they could sometimes break apart.

17 At one time the tendency of solid objects to fall to the ground was considered fully explained as that was the natural place for solids.

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Anthropomorphic and animalistic talk/thought.

Teachers use anthropomorphic language - by habit or design - without meaning to imply that they imbue consciousness to individual atoms and the like. When students report that an atom thinks it’s got two electrons (T1-A113), or can move about if it wants (T4-A085), or that an ion can have as many bonds as it wants (C1.262), or that a bond is trying to be ionic (C1.473) this may not be any more than a convenient way of describing (and perhaps avoiding trying to explain) what is happening. Nevertheless such talk is worthy of following up to find out what the students intend to suggest.

Use of analogy.

Analogy and metaphor are often used as teaching/learning devices to bridge between the known and the novel. One common analogy is that between the atom and the solar system (with the latter assumed to be the more familiar idea.) K used this analogy in the other direction, suggesting that planets shield the effect of the sun in a similar way to that of core electrons shielding valence electrons from the nucleus (K3-B101.) Such an idea is inappropriate and shows the hazards of using a model, without discussion of its limitations.

Distinguishing microscopic (molecular) and macroscopic (molar) phenomena.

In a subject that attempts to explain the nature of macroscopic materials (iron, salt, wood, water, air and so forth) through theory based on the behaviour of microscopic hypotheticals (atoms, electrons, molecular orbitals etc.) it is important to distinguish clearly between these two levels. When subject N shows confusion between the meaning of the fundamental terms ‘element’, ‘molecule’, ‘atom’ and ‘compound’ (N1-A082) this suggests that remedial action should be taken. Of course confusion in using words does not necessarily imply confusion between the concepts those words represent, but in an in-depth interview it is possible to investigate whether the confusion is at the level of ideas or labels.

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For example subject L considered that a compound could not be pure, as it contains more than one element (L2-A180), showing a definite confusion over the idea of a single substance at the molar and molecular levels.

Views of reality.

It is interesting when students make comments that relate to the ontological status that constructs have for them. For example subject T considers an atomic orbital to be the probability (T3-A453) or likelihood of finding an electron in a certain place (T5-A346) and considers that an orbital which is not occupied by electrons (i.e. probability/likelihood of finding electron there is zero) “wouldn’t be an orbital” (T3-A336). T also had a view about electron-spin: it doesn’t really mean anything (T5-A378).

When C was asked if she though a particular molecule was flat, as it appeared in the diagram, she replied that she didn’t think anything was really flat: a comment that in retrospect I would like to have followed-up further!

Learning through talking.

The dialectic process is meant to uncover truth through comprehensive questioning. In my research interviews students sometimes talk themselves into new knowledge (i.e. make new links between existing ideas) with only a limited catalytic effect from the researcher. For example subject N appeared to independently arrive at the idea of Van der Waals interactions through her own talk (N1-A557, see appendix B), whereas in a normal teaching situation many students find this a difficult concept to assimilate.

Pseudo-arguments.

Respondent interviews allow the subjects the opportunity to develop arguments and explanation. Some students are capable of quite extended bouts of logic. However, just as interesting, are - what I have come to label - pseudo-arguments. By this I mean that the student will present a sequence of propositions which has the grammatical structure of an

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argument, but not the semantic content! Sometimes the argument is a tautology, whilst on other occasions it may be teleological. A pseudo-argument may be (what seems to the interviewer) a series of unrelated comments connected with “because”, “as” and “therefore”. An interesting type of pseudo-argument is that whereby the connection made is an orthodox one, but - from the viewpoint of that orthodoxy - cause and effect are exchanged: for example the suggestion that the elements fluorine, oxygen, nitrogen and chlorine are not metallically bonded, because they are non-solids (T3-B323).

Visualisation as an aid to understanding.

The stimulus diagrams used are obviously drawn on flat pieces of paper, and this introduces distortions. Some representations distort angles to ‘squash’ a solid entity into two dimensions, whilst other diagrams take a cross-section. Teachers and text-illustrators obviously know what they intend - and sometimes seem to forget to make this explicit. Students have had less practice at visualising atoms and molecules, and their constituent parts. During one interview subject T reported that he could not picture carbon atoms moving in a lattice (T4-A358) - although he was not sure why 18. In future work it will be interesting to explore the extent to which subjects feel they can visualise microscopic chemical entities.

Methodological issues.

In my pilot study one main data collection technique was used: semi-structured respondent interviews. This restriction is justified in such a pilot as one needs to assess the fruitfulness of the methodology, and to develop both the interview foci, the questioning technique, and the procedures for analysing data. However there are a number of questions of authenticity of the research that need to be considered. As the interviewer is a chemist, with experience teaching at both (what would now be called) KS4 and A level, some face validity is ensured. As an in-depth interviewing technique is applied it is possible to distinguish ‘off-hand’ responses made for the sake of producing an answer, from firmly held ideas. For example the interviewer can mentally note an interesting response and attempt to return to the theme later in the interview. However, there are a number of serious questions that can be raised 19 .

18 The discussion was about the difficulty in melting diamond. T could not explain this. He was asked to picture a diamond lattice, (which he could) and to imagine the atoms moving around (only possible if the bonds are broken or distorted) but he could not visualise this, and was unable to explain why. He was able to visualise an array of spheres (with the bonds removed) moving about though, and accepted that the bonds make a difference.

19 It might be suggested for example that a different teacher-interviewer may have elicited different responses, and that no measure of ‘inter-observer reliability’ is possible from such a study. This is true, and is

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I will discuss some of these in the form of a series of questions and answers:-

How do I know that a different response to a stimulus diagram several months later represents a development of thinking, rather than a tendency to say the first thing that comes into the subject’s head?

This is a serious criticism, and especially so in that one of my early subjects, C, certainly seemed to operate a ‘random thought generator’ at times, that had her make a suggestion, and as soon as it ceased to be fruitful, discard it for another - often contradictory - proposal. With the current cohort, I intended to carry out a second interview fairly soon after the original data collection to see if responses are consistent. However the time lapse was still too long in view of the amount of formal teaching and independent reading taking place. When I enter the next phase of the project I intend to have fewer subjects to allow a shorter period between interviews with individual students 20.

In the pilot study the first interview took place during the second term, and although the students had not studied the bonding topic in depth they had covered the key idea of electronegativity, and bonding ideas had been used in their organic classes 21, so the enquiry did not necessarily uncover their ideas at the start of the course.

This was a problem in the pilot, but the current cohort were recruited at the start of their course and interviewed as soon as possible after, to overcome this.

always a limitation of single-researcher studies. The only response to this is that it is in the nature of research that findings should always be subject to replication elsewhere.

20 Part of the problem is the availability of times when the students and myself are both free to carry out interviews, but a more serious constraint is the backlog of data analysis. Worthwhile follow-up interviews require at least a provisional analysis of the data to be followed-up! Although I was aware of the logistics of this process when I started off the current cohort I was only aiming to take on three or four subjects. I was rather surprised when twelve of the class volunteered themselves, but felt that I should take on all those interested, as I believe the process undertaking these research ‘tutorials’ is beneficial for the students. I also expected a large drop-off of interest, as I was asking for volunteers during the first week of college when enthusiasm for the novel A level studies was high, but only two of the original volunteers decided not to be interviewed after thinking it through, and two more have dropped out since (one left college for a job, the other is dropping chemistry.)

21 Both the classes that the original pilot and current cohort were drawn from were taught by several lecturers. The researcher teaches a course in inorganic chemistry, which includes some of the basic general chemical theory, but the organic and physical chemistry is taught separately, in parallel.

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As there is a single interviewer, and this researcher prepared the focal diagrams to act as a stimulus, it is quite possible that there is a strong interviewer bias in the aspects of the topic which are seen as most significant, and therefore represented in the diagrams and questioning. Respondents may reflect this rather than discuss the aspects of bonding they see as most relevant.

In the pilot there was no attempt to overcome this objection. However the current cohort have undertaken additional activities. In one early session they have been asked to list any types of chemical bonding they are aware of, and then to draw their own representations of these classes of bonding. They have also been asked to complete a repertory grid procedure to uncover their own significant constructs, using triads of cards prepared from published chemistry textbook diagrams, rather than figures drawn for the research. It is intended to use this data as a triangulation technique for comparison with the interview data.

Both the respondent interviews and repertory grid sessions are conducted in a one:one::researcher:subject context. Is there any evidence that that the subjects use the same ideas in interaction with peers as with the researcher?

I have recently added a new strand to the research, whereby I tape-record pairs of students discussing a past examination question. In this context the perceived authority and power of the subjects is more evenly shared than in conversation with the teacher-researcher, and the discussion can take the form of negotiation rather than an interrogation! I intend to develop this aspect of the research further.

Finally, 1:1 interviews, repertory grid technique and even didactic pairing of subjects all take place in a clinical setting: separated from the classroom context around which learning is normally based. Is there any evidence that the data collected is typical of the normal way that the subjects think about this topic during their course?

Again with the present cohort some effort has been made to collect supporting data. Certain work produced as a normal part of the course is relevant to this study, and copies have been taken to keep on file, for comparison with the clinical research data 22 .

22 For example, after teaching the topic of periodicity, a past examination question on atomic ionisation energies was used as an assessment. The concepts involved in answering this question (atomic structure, force, energy) were amongst those underpinning an understanding of chemical bonding, and the subjects answers were photocopied before being returned to them.

14


Summary.

In this paper I have discussed an enquiry into student understandings of chemical bonding at A level. I have explained why I think this is an important topic area, and also why I feel it has been somewhat neglected in previous research. I have given a brief taste of the type of data that can be collected through respondent interviews, and I have discussed how I am expanding the research methodology to increase the authenticity of findings from such an interview study.

Acknowledgements are due to Dr. Mike Watts (Roehampton Institute) for stimulating discussion, Havering College - and my Colleagues at Havering - for supporting my interest in this area, and Merton College, Oxford for awarding a Study Visit during July 1990 which allowed me to undertake an initial literature search.

15


References:

Carmichael, Patrick, Rosalind Driver, Brian Holding, Isabel Phillips, Daryll Twigger and Mike Watts,

Research on students’ conceptions in science: a bibliography, Children’s Learning in Science Research

Group, Centre for Studies in Science and Mathematics Education, University of Leeds, 1990 (plus addenda,

1991, 1992).

Driver, Rosalind and Gaalen Erickson, Theories-in-action: some theoretical and empirical issues in the study

of students’ conceptual frameworks in science, Studies in Science Education, 10, 1983, pp.37-60.

Fischler, Helmut, & Michael Lichtfeldt, Modern physics and students’ conceptions, International Journal of

Science Education, 14 (2), 1992, pp.181-190,

Gilbert, John K., and D. M. Watts, Concepts, misconceptions and alternative conceptions: changing

perspectives in science education, Studies in Science Education, 10, 1983, pp.61-98.

Gilmore, G. N., A Complete ‘O’ Level Chemistry, Cheltenham: Stanley Thornes, 1978.

Hart, Richard, Chemistry Matters, Oxford: Oxford University Press, 1978.

Jiménez-Aleixandre, María P.,Thinking about theories or thinking with theories?: a classroom study with

natural selection, International Journal of Science Education, 14 (1), 1992, pp.51-61.

Kuhn, Thomas S., The Structure of Scientific Revolutions, 2nd edition, Chicago: University of Chicago,

1970.

Peterson, Ray, David Treagust & Patrick Garnett, Identification of secondary students’ misconceptions of

covalent bonding and structure concepts using a diagnostic instrument, Research in Science Education, 16,

1986, pp.40-48.

Pope, Maureen & Pam Denicolo, Intuitive theories - a researcher’s dilemma: some practical methodological

implications, British Educational Research Journal, 12 (2), 1986, pp.153-166.

Pope, Maureen & Mike Watts, Constructivist goggles: implications for process in teaching and learning

physics, European Journal of Physics, 9, 1988, pp.101-109.

Popper, Karl, R., The Logic of Scientific Discovery, London: Hutchinson, 1959.

16


Scott, Philip, in association with Tony Dyson & Steven Gater, A constructivist view of learning and teaching

in science, Leeds: Centre for Studies in Science and Mathematics Education - Children’s learning in science

project, June 1987.

Swift, D. J., D. M. Watts & M. L. Pope, Methodological pluralism and personal construct psychology: a case

for pictorial methods of eliciting personal constructions, paper presented to the 5th International Conference

on Personal Construct Psychology, Boston, Massachusetts, July 1983.

Taber, Keith S., Development of the concept of chemical bonding in advanced level students, paper presented

as a poster to the 11th International Conference on Chemical Education, York, 1991.

Taber, Keith S., Developing understanding of chemical bonding: the toolbox analogy, unpublished working

paper (available from the author), January/June 1993 (1993a).

Taber, Keith S., A procedure for on-going analysis of interview data during a research project into conceptual

development, unpublished working paper (available from the author), June 1993 (1993b).

Taber, Keith S., Understanding the ionic bond: student misconceptions and implications for further learning,

paper to be presented to the symposium ‘Research and Assessment in Chemical Education’ (22.09.93) at the

Royal Society of Chemistry Autumn Meeting, Warwick, 21-23.09.93 (1993c)

Watts, Mike, & Di Bentley, Constructivism in the classroom: enabling conceptual change by words and deeds,

British Educational Research Journal, 13 (2), 1987, pp.121-135.

Watts, D. Michael, & Maureen Pope, A Lakatosian view of the young personal scientist, paper to the British

Conference on Personal Construct Psychology, UMIST, September 1982.

Watts, Mike, & Maureen Pope, Thinking about thinking, learning about learning: constructivism in physics

education, Physics Education, 24, 1989, pp.326-331.

Wightman, Thelma, in collaboration with Peter Green and Phil Scott, The Construction of Meaning and

Conceptual Change in Classroom Settings: Case Studies on the Particulate Nature of Matter, Leeds:

Centre for Studies in Science and Mathematics Education - Children’s learning in science project, February

1986.

Zoller, Uri, Students’ misunderstandings and misconceptions in college freshman chemistry (general and

inorganic), Journal of Research in Science Teaching, 27 (10), 1990, pp.1053-1065.

17


Appendices.

Appendix A: alternative conceptions of bonding.

Metallic bonding.

Where students have not been introduced to metallic bonding they are sometimes, understandably, unwilling to

suggest what types of interaction might be present in metals. Other students will try to construct an explanation

based on their existing frameworks of ideas. When subject N was shown my stimulus figure 6 (see appendix C)

she did not consider that bonding was represented, and did not think there would be a strong attraction between

what she identified as an arrangement of iron atoms (N1-A431). She suggested that the iron atoms were held

together by some form of gravitational interaction (N1-A447). N did not think there was any chemical bonding

involved, as there was no evidence in the figure 23 for covalent or ionic bonding, and she was not aware of any

other type of bonding (N1-A484). When she was next shown a more detailed diagram of a metal structure (my

focus figure 80 24) she misinterpreted this as ionic bonding (N1-A490). In a later interview N was asked about

bonding in metals, and she tried to explain her understanding of such bonding in terms of electrostatic

interactions and van der Waals forces (N2-A161). Although technically metallic bonding is distinct from van

der Waals forces, such a suggestion was quite sensible and demonstrated that N was able to try an apply her

knowledge of chemical ideas in unfamiliar contexts.

Ionic bonding.

Whereas subjects were often ignorant of any mechanism by which metals might be bound, students embarking

on A level chemistry seem to have a model of ionic bonding. Despite my limited sample, there is some

suggestion from my early results that alternative conceptions of ionic bonding are quite common 25. One

student had a particularly tenacious conception, discussed in the main paper - and in more detail below - that

interfered with her attainment of the ‘accepted’ model of ionic bonding and led to considerable confusion.

More common seems to be a misidentification between ion formation and ionic bonding. Ions are formed when

metal atoms donate negatively charged electrons to non-metal atoms to form positively charged cations and

23 the diagram just shown close packed circles, no overlap (which might suggest covalent bonds) or charges (which would imply ionic bonding).

24 which showed metal cations and small particles meant to be the delocalised electrons25 A more detailed examination of this topic will form the basis of a paper to be presented to the Royal

Society of Chemistry Autumn Meeting (Taber, 1993c.)

18


negatively charged anions. This process of electron transfer may be understood 26 as an interaction between a

small number of specific atoms: e.g. one chlorine atom accepts one electron from one donor sodium atom.

However the sodium chloride ionic lattice contains sodium cations equidistant from, and equally attracted to,

six chloride ions (and vice versa). Even if it were possible to identify a specific ion pair that had undergone

electron transfer, there would be no ‘memory’ of this in the lattice: the interaction between such a pair of ions

depends only on their charges and the distance (between the centres of charge), and would be no greater than

between any other pairing at the same separation. The concept of a molecule, so useful in most covalent

substances, is of little value here, and if used would probably be best applied to an entire crystal grain. It is

meaningless to identify ion pairs as ‘molecules’ within the solid lattice 27. However subject J identified fifteen

molecules (J1-A141) in the figure of sodium chloride, and subject T described an pair of ions as a molecule

(T1-A459). Subject N reported that chlorine could only form one bond, but would also bond with other ions

(N1-A313), then clarified this by suggesting that there would be one stronger bond between a chloride ion and

a specific sodium ion, rather than the ‘just attractions’ 28 with other sodium ions (N1-A328). T also showed

some confusion on discussing the diagram of ionic bonding (focus figure 5), reporting that sodium could only

bond with one chloride (T1-A459), but then deciding that a cation was equally bonded to all four (shown)

surrounding anions (T1-A482). Later when discussing a diagram (focus figure 32) representing ion formation T

returned to the idea that a cation could only form a bond with an anion it had transferred an electron to (T1-

B563), but that in an ionic lattice there were two factors causing an attraction between ions: the opposite

charges, and the transfer of electrons (T1-A556). A similar line was followed by subject K who suggested that

an ion may be attracted to several surrounding counter ions, but was only bonded to one (K1-A313). Although

diagrams such as my focus figure 5 seemed to show several equidistant counter-ions, K proposed that this was

a distortion of the way the diagram represented the lattice: in three dimensions each sodium ion was attracted

to one chloride ion (K1-A169).

When she was first interviewed A was aware of a category of bonding called ionic, which occurred between

metals and non-metals (A1.578). When shown focus figure 5 A did not think it represented ionic bonding, but

“just sodium and chlorine atoms” (A1.238) with no bonding between (A1.240), as “they don’t actually overlap

or anything” (A1.242). A should have learnt at GCSE that the ‘+’ and ‘-’ signs were meant to indicate ions.

However A had her own personal construction for these symbols: they showed the number of electrons over or

under a full outer shell of electrons. Na+ was a sodium atom with one electron more than a full outer shell -

with electronic configuration 2.8.1 (A1.272) - and Cl- was a chlorine atom with one electron short of a full

shell (A1.262).

26 although the metal atoms are part of a metallic lattice structure, and the valence electrons are delocalised!

27 although such ion pairs may exist in the vapour, and at least transiently in the melt, or in solution.28 it is not uncommon for subjects to imbue the word ‘bond’ with some special significance beyond being

a strong attraction between chemical species.

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Later in that year A was interviewed again, after the topic of bonding had been formally studied at A level.

Once again for A the figure shows “atoms of sodium and chlorine” (A2.33) rather than ions. However further

questioning shows that (after some thought) A was able to correctly assign the electronic configuration of 2.8

to Na+ (A2.43). Some ambiguity appears when after she has identified Na+ and Cl- as ions A is asked what the

‘+’ symbolises: “it represents the electron that’s been lost. So giving it a positive charge. Because it would

have been positive. And the chlorine, like an electron has been added, to give it, to make it up to the full shell.

So like it’s minus an electron really” (A2.53). This interesting statement is worthy of deconstruction. Parts of it

may be understood on the conventional interpretation that symbols such as ‘ + ’ represent an overall electrical

charge, whilst other comments seem to revert to the earlier meaning of deviation from noble gas electronic

configuration. As this interview continued A showed on a number of occasions that she was able to use the

conventional meaning for the ‘+’ and ‘-’ symbols; however there were also occasions when she switched to her

alternative interpretation. For example in order to form a neutral species from aluminium ions (Al3+) and sulphate ions (SO42-) A suggested four aluminiums and two sulphates (A2.226). This response makes no sense

in terms of the conventional meaning of the charge symbols, but for A “it would make eight, so it would be

neutral” (A2.230). Eight extra electrons make a full shell, and so that is a neutral species within her ‘deviation

from noble gas electronic configuration’ framework.

One year later, with A only about one month from her final examination there was still evidence of confusion.

Figure 5 showed “sodium and chlorine molecules, or atoms. Probably making sodium chloride I would hazard

a guess at.” (A3.28) Was there any bonding in the structure represented?

“In the structure represented it shows circles with sort of plus and minus signs in. So it’s really showing sort of the sodium and chlorine ions and not actually showing any way they're bonding, because if they were bonded, then there would an overall sort of neutral charge, because of the donation of electrons, neither would have a plus or a minus charge, so, I would say that that hasn’t got any bonding in it, because they’ve still got their original charge, or the ionic charge on them. If you get a molecule of sodium chloride, the overall charge is neutral, due to the fact that the sodium’s donated an electron, and the chlorine’s accepted, an electron.” (A3.30, emphasis added.)

Even after five and a half terms of advanced level chemistry tuition A had an alternative conception of the

charge symbols that prevented her acquiring a consistent understanding of ionic bonding. 29

29 The identification of this persistent misconception at this late stage led to a hasty tutorial to try and help A assimilate the orthodox understanding. A follow up interview showed that this had been somewhat successful, although A still referred to a chlorine atom as being “sort of minus an electron” (A4.22)

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Appendix B: Transcript samples.

Two small samples of transcript are given: the first is an extract from a full transcription of one of the pilot

study recordings, and the second was prepared especially for this paper.

In both cases ‘I’ refers to the interviewer.

A’s conception of the forces binding the nucleus (prior to formal teaching.)

From interview A1.

20 I: No? Can you identify the different parts of that diagram? What’s the blob in the

centre?

21 A: It’s the nucleus.

22 I: That’s the nucleus. Do you know what’s in the nucleus?

23 A: The protons and, no the electrons and the neutrons, no the protons and the neutrons.

The electrons are round the outside.

24 I: There’s protons and neutrons in the centre okay.

25 A: Yeah.

26 I: Erm, what holds them together, any idea?

27 A: Is it the forces from the outer ring? Outer rings or outer shells? The electronic

forces?

28 I: What repelling them in? Holding them

A: yeah

I: in the centre? It could be.

29 A: Pushing them.

21


N constructs an understanding of intermolecular forces between neutral species (prior to formal teaching.)

From interview N1 starting at tape counter: A553 30

1 I: Number 17, have you any idea what number 17 is meant to be?

2 N: • • • It’s two iodine molecules, I’m sorry atoms, • • • no I’m not sure what that is.

3 I: So there’s two iodine atoms,

4 N: yeah

5 I: and apart from that you’re not sure?

6 N: They’re bonded together somewhere

7 I: So where’s there a bond?

8 N: Between the two, • semi-circles around them.

9 I: Ah right, so how many bonds do you think there is in the total diagram, the whole

diagram?

10 N • • • Twelve?

11 I: So is that inside each of these, ‘peanut’ shapes?

12 N: Yeah

13 I: Yeah? So, is there any, any kind of bonding you think, between one ‘peanut’ shape

and another?

14 N: Yeah there should be

15 I: There should be?

16 N: Mm

17 I: What kind of bonding would that be?

18 N: Think it would be charge, attraction between charges again.

19 I: Attraction between charges, so is that ionic is that?

20 N: No it won’t be ionic,

I: Won’t be ionic?

N: but it would be attracted to, the rest of it.

21 I: So they’ll all be attracted together will they? • So which particles there are charged?

22 N: They won’t be charged particles individually, but, but some will be slightly positive

and others slightly negative, and that will cause, like a weak attraction, between them,

holding them together.

23 I: So where might there be a slightly positive charge, whereabouts?

24 N: Erm if the electron, • • if the electron on one of them is nearer to the end, nearer to

the, • if one electron’s nearer to:wards the centre of the, iodine molecule and the other’s

30 Where full transcripts have not been prepared analysis of the recordings has been based on indexing the interviews according to tape counter numbers. This process is discussed in a working paper: Taber, 1993b.

22


further out, the one, bit where it’s further out’s going to be slightly more negative, than

where it’s empty. And so on the other side if it joins to the bit where it’s empty, it’s

slightly positive, and so they’ll attract, sort of, (something like that.)

25 I: That’s interesting. I’ll just have a quick look at how the tape is doing 31. Right, erm,

• did you, has somebody told you that, or have you just thought of that, or is that

something you’ve just sort of argued out, or that something that somebody’s taught you?

26 N: That’s what I think is going on anyway.

27 I: Sorry? {not hearing}

28 N: Just thought it out.

29 I: So nobody’s ever told you that, you haven’t sort of written that down ion a class

somewhere, you just made that up, did you?

30 N: (Did I?) Yes!

key:

{curly brackets}: interpretation added for information

(round brackets): comments made sotto voce, apparently to self

struck through: indistinct on recording, less confidence in accurate transcription

31 I was aware that the tape was near the end of the side, and was worried it was about to run out at this most interesting point in the discussion!

23


Appendix C: Sample of the foci diagrams used during the research.

Figure 5.

This figure was meant to represent a lattice arrangement with ionic bonding.

24


Figure 6.

This figure was meant to represent a close packed metallic lattice.

25


Appendix D: The subjects

The subjects discussed in this paper were previously, or are currently, students taking an A level chemistry

course in an F.E. College.

The students are referred to by letters. The recorded interviews cited are referred to by alpha-numeric code

(e.g. A1, etc., see Taber 1993b for details.)

A: born: May 1974

entry grades: GCSE: ABBBBCCCC, including chemistry

A levels: chemistry (D), biology (C), government & politics (C)

proceeded into HE to study humanities based degree

A1: second term, first year; A2: third term, first year; A3: third term, second year; A4: third term, second year.

B: born: May 1974

entry grades: GCSE: AAAAAAAABB, including chemistry

A levels: chemistry (B, 2 on S paper), biology (A), pure mathematics & statistics (A)

proceeded into HE to study chemistry

B1: second term, first year; B2: third term, first year; B3: third term, second year.

C: born: September 1973

entry grades: GCSE: AAABBBBBB, including chemistry

A levels: chemistry (D), pure & applied mathematics (N), physics (studied first year only)

proceeded into HE to study science based course

C1: second term, first year; C2: third term, first year.

J: born: September 1975

entry grades: GCSE AAAAAABB, including science

A levels chemistry, biology, pure mathematics & statistics

J1: first term, first year; J2: second term, first year.

K: born: May 1975

entry grades: GCE O: AAABCC, including chemistry


K1: first term, first year; K3: second term, first year.

26


L: born: August 1976

entry grades: GCSE: AAAAAAABBC, including science


L2: second term, first year.

N: born: July 1976

entry grades: GCSE: AAAAAAAA, including science


N1: first term, first year; N2: second term, first year.

T: born: May 1976

entry grades: GCSE: AAABBBBCC, including chemistry

A levels chemistry, geography, pure mathematics & statistics

T1: first term, first year; T2: second term, first year; T3: third term, first year; T4: third term, first year; T5:

third term, first year; T7: third term, first year.

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