The importance of the study
Chapter 1 of Understanding Chemical Bonding: The development of A level students' understanding of the concept of chemical bonding
Introduction to the thesis. The importance of the study
"At the most general level there are a few concepts that are very integral to the way in which chemists approach the natural world. Concepts like bonding, structure, rate of reaction, and internal energy apply to all chemical systems. These are … powerful ideas that provide structure for whole areas of knowledge. Once such a concept is grasped it provides a framework in which the learner can confidently face new learning … As the learning itself proceeds the understanding of the concept itself grows ever richer."
Fensham, 1975, pp.199-200, italics in original.
§1.0: The character of the research
This thesis discusses aspects of how understanding of the concept 'chemical bond' develops. The research was undertaken with students following a General Certificate of Education Advanced Level (henceforth 'A level') Chemistry course in a Further Education College in England. These learners would have been introduced to some basic ideas about chemical bonding during their school courses, at the General Certificate of Secondary Education level (G.C.S.E. – now known as Key Stage 4 (KS4) in the English school system). Learners' ideas about chemical bonding were elicited near the start of their A level course, and then their progression was investigated.
The thesis is based on a small scale study primarily using in-depth interviews with individual learners taking A level chemistry at a single centre. (A schedule for the interviews is provided in appendix 1, along with a digest of the other data analysed for the research.) In this sense the research is somewhat provisional in nature. However, the research has followed the principles of 'grounded theory' (discussed in chapter 4), in that data has been collected and analysed to build a model (presented in chapter 6, and discussed in chapter 12) which is suitable for formal testing. Although some provisional survey work has been carried out to demonstrate the feasibility of testing the general applicability of the model (described in appendices 2 and 3), the present thesis is primarily concerned with the development of the model
as an authentic interpretation of the data collected, rather than with its testing. In this introductory chapter I will explain the importance of the focal concept of chemical bonding, and why developing understanding of this concept is an important research topic in science education.
§1.1: The importance of the chemical bond concept
Chemical Bonding is a key idea in chemistry which is used at all educational levels, and which is needed for an understanding of much of the subject. Fensham has called it one of the "big concepts in chemistry" and (in the quotation used as a motto above) described it as one of the "powerful ideas that provide structure for whole areas of knowledge" (Fensham, 1975, pp.199-200).
Chemistry may be defined as the science that characterises material substances, in particular through their interactions (for example the Longman Modern English Dictionary defines chemistry as "the study of the composition, properties and structure of substances, and of the changes they undergo", Watson, 1968, p.188). Although such chemical reactions could be – and historically have been – studied descriptively, chemistry as a science seeks to explain observed patterns in terms of a theoretical framework. Central to this framework is the notion that all substances are comprised of arrangements of elemental particles bound together, and that reactions involve rearrangements of these particles. Thus chemical reactions involve the breaking and making of chemical bonds, and explanations of chemical reactivity relate to the reasons for, and mechanisms of, bond breaking and bond forming.
The particles often described as elemental in chemistry are atoms (although it will be argued in chapter 12 that this may not be the most appropriate conceptualisation). In terms of the theoretical framework, chemistry may be considered to be largely about the rearrangements of groups of atoms, and therefore about the making and breaking of bonds between atoms. Indeed, chemistry has been described as "the making and breaking of chemical bonds" (Linnett, quoted in Pickering, 1977, p.1), and it has been claimed that understanding the chemical bond is central not only to chemistry, but "to all fields of molecular science" (Zewail, 1992, p.xi).
The centrality of this topic to chemistry is recognised by the Associated Examining Board which sets the syllabus for the A level Chemistry examination that is sat in the College where the research was undertaken (Associated Examining Board, 1996). Indeed at the time of writing the A level Chemistry syllabus content is "arranged into four major themes" the first of which is "Structure and Bonding" (the others being "Physical Chemistry", "Inorganic Chemistry" and"Organic Chemistry").
Textbooks intended to support A level chemistry courses usually have one or more chapters on bonding as part of the early material which provides the theoretical foundation for the subject (e.g. Ch.5 of Andrew and Rispoli, 1991; Ch.2 of Atkins et al., 1988; Ch.2 of Freemantle, 1987; §1.5-§1.6 of Fullick and Fullick, 1994; Ch.8 – Ch. 10 of Hill and Holman, 1989; Ch.3 of Lister and Renshaw, 1991; Ch.4 – Ch.6 of Maple, 1996; Ch.4 of Ramsden, 1994).
§1.2: The importance of studying learners’ ideas in science
In the past two decades there has been a great deal of research in science education looking at various aspects of student learning and learning difficulties. This was a response to studies which had drawn attention to difficulty that secondary schools pupils had understanding the conceptual base of physics and chemistry (Driver and Easley, 1978, p.79). This has been particularly so in the tradition of work described as the 'alternative conceptions movement', or 'constructivism', which is reviewed in chapter 2. The assumption has been that the more that is understood about learners' ideas about a topic, the more effective curriculum planning and teaching may be (e.g. Driver, 1983, p.76, c.f. §2.3.9, §2.3.10).
The centrality of chemical bonding to the study of chemistry makes it a fundamental concept area, and science teachers looking to educational research to inform and illuminate their teaching, might expect to find many informative studies discussed in the literature. In fact, this is not the case (Carmichael et al. 1990, Duit, 1991).
§1.3: The relative paucity of studies into student understanding of bonding
There has been a great deal of research into learners' ideas about scientific topics (for example see the bibliography by Carmichael et al. 1990, and annual updates), much of it undertaken within the 'alternative frameworks' or 'constructivism' perspective (to be discussed in Chapter 2). However some areas of science have attracted more attention than others.
For example Duit (analysing another bibliography) reports 132 studies classified within the whole of chemistry, compared to 146 in Electricity and 281 in Mechanics – the two most 'popular' areas for research within physics (1991, Table 4.1, p.71). The chemistry-related studies covered areas of combustion, oxidation, chemical
reactions, transformation of substances, chemical equilibrium, symbols, formula, mole concept – but not bonding. The bibliography referred to above, produced by Carmichael et al., (1990) contains only six references to studies of learning about bonding and structure. (Griffiths reports how he only found three papers that related to bonding, and, even then, "one of them … incorporated all of the information contained in the other two", 1994, p.77).
So despite the accepted importance of chemical bonding as a concept, and the considerable activity of educational researchers investigating the understanding of various aspects of science, little attention has been paid to the topic of learners' understandings of chemical bonding. Although it is not possible to know exactly why this should be, it is possible to suggests three plausible factors:
- the nature of chemical knowledge (§1.3.1)
- the absence of preconceptions (§1.3.2)
- prerequisite knowledge (§1.3.3)
It will be argued that these factors
(1) make this a more complex area to investigate than others that have received much more attention from researchers (such as mechanics), and
(2) put such a study outside the 'main stream' of constructivist studies in science education.
However, in the present research these same factors were considered to provide extra interest to the work, as it is my intention that through this thesis I should contribute to the wider debates about (a) appropriate models of learning and progression in chemistry; and (b) suitable methodology for studies into student learning of science.
§1.3.1: The nature of chemical knowledge
Chemistry, although an empirical science, has an extensive and rich theoretical structure. The same could be said of physics – where student understanding has been probed in much more detail – but it is my contention that the structure of theoretical knowledge in these two sciences is significantly different (c.f. §1.7 below). Both subjects may be understood to involve building models. In physics these models are largely mathematical and to a large degree consistent across the subject (Gregory, 1988, p.vi, p.18. It should be noted that I am referring here to the formal public version of science as represented by the research literature, and not the personal knowledge of individual scientists which may well be less consistent: c.f. §1.7, below). Indeed where discontinuities do appear in the theoretical structure they receive much attention. (Perhaps the major examples are the shift from Newtonian mechanics to the alternative framework based upon Einstein's paradigm, and the apparent incompatibility of quantum mechanics with traditional branches of physics.) The basic concepts of physics include energy, force and momentum – concepts for which there are consensus meanings among physicists. Although it is possible to reduce the discussion of much of chemistry to applications of physics, this is not the way most chemists see the subject (e.g. Scerri, 1993.)
The perceived key concepts of chemistry are often those that are derived within the complex theoretical structure of the discipline – rehybridization, the inductive effect, polarisability, acids, oxidation, nucleophiles, resonance. Although it would be possible in principle to ultimately redefine such concepts in terms of a conceptual hierarchy based on a few fundamental concepts, this has not been how chemists perceive the subject. Whereas in physics practitioners are often content to conceptualise their subject in terms of a small number of fundamental ideas (charge, energy, etc.) in chemistry the subject is often developed by 'bootstrapping' one high level concept on another – a process that may readily become circular. (However this need not be a problem if, as Kuhn {1977, pp.xviii-xix} suggests, the meaning of concepts in science is not actually learnt through formal definitions, but by working through examples). In the case of concepts such as chemical bond, acid or oxidising agent there is no single definition as with momentum (i.e. p = m.v), but a series of meanings of different sophistication which are applicable in different specific contexts. Appendix 4 sets out an analysis of the concept of chemical bond as it might be discussed at KS4 (G.C.S.E.) level, and the additional discussion that might be introduced at A level. The abstract and multifaceted nature of the concept area being studied may readily grasped from this analysis.
The researcher who investigates student understanding of the force concept will be aware that the concept may be understood to different degrees, but should have a clear idea of what the physics meaning of force is. The researcher exploring student understanding of some chemical concepts has no single 'benchmark' for comparison.
As Paradowski has commented,
"In physics it is possible to develop a simple and detailed model to explain certain classes of phenomena, but chemistry is too complex to be fully explained by such simple theories … one needs several good models. But these 'good' models are more flagrantly models, i.e. they explain only a selection of data, and hence the need for several models."
Paradowski, 1972, quoted in Brock 1992, p.505
In my view this makes the work more interesting and rewarding, but this could well be one reason why understandings of chemical concepts have been explored less than those in physics, and why a key idea such as the chemical bond has received sparse attention. This issue will be discussed further, below (§1.7).
§1.3.2: The absence of preconceptions
Much of the research into the understanding of scientific concepts has taken place from perspectives that has been collectively termed the 'alternative conceptions movement' (see chapter 2) which itself had roots in Piagetian studies into children's unschooled ideas about the world (§2.2.1).
Children have direct experiences they will associate with – for example – gravity and electricity, plants and the sun. They will form ideas about such phenomena. Children's experiences of chemical bonds are very indirect – and indeed it is unlikely that someone would come to hold a conception of chemical bonds in the absence of explicit teaching about atoms and molecules. Certainly learners would be expected to be familiar with the term 'bond' (as in glues, or family ties), and to bring their 'life-world' meaning of the word to classes. However, without some notion of the structure of matter at a molecular level, preconceptions about chemical bonds are unlikely to develop. Carr has pointed out that although learners' understanding of some science concepts is hindered by their everyday meanings for the word and their intuitive explanations of the phenomena,
"Confusions and difficulties over a number of chemical concepts may require a different perspective, since these are abstract and formal explanations of invisible interactions between particles at a molecular level and are not likely to be arrived at from confrontation with the world of experience."
A similar point is made by Garnett et al., who have reviewed the literature on students' alternative conceptions in chemistry, and come to the view that some of the alternative ideas reported may well derive in part from the way topics are taught,
"while there are many possible origins for these alternative conceptions as students construct new meanings based on the 'informal' or 'commonsense' knowledge they bring to instruction, our view is that some of these conceptions result from pedagogic practices, and, with carefully constructed instruction, their incidence could be reduced."
Garnett et al., 1995, p.72
(This possibility will be acknowledged below in the notion of an epistemological learning impediment, §1.5.5.)
Researchers interested in cataloguing quaint but false ideas about nature are more likely to investigate areas where young people form spontaneous conceptions, or 'intuitive theories', about natural phenomena. This is a second plausible reason why so little work has been carried out on understanding of bonding.
§1.3.3: Prerequisite knowledge
Closely related to the last point is the extent of the prerequisite knowledge
required for learning about chemical bonds. The importance of analysing a topic area to ensure that the required prerequisite learning is in place before the topic is taught is well established in chemistry (e.g. Gilbert, 1977, p.11; Kempa, 1977, pp.3-6).
Before students can effectively study bonding they must have some ideas about pure chemical substances compared to mixtures, and about the atomic theory, or 'particle theory'. These are topics which have received research attention, and where learning difficulties have been uncovered (see chapter 3, §3.1.1 and §3.1.2).
Further, in order to develop a suitable understanding of bonding concepts at A level, the learner needs to already understand basic electrostatic ideas involving the fundamental physics ideas of force and energy (see appendix 4 and 5). Again these are areas that have received considerable research attention, and have been found to be difficult for learners (§3.1.3).
The investigator hoping to enquire into the understanding of chemical bonding needs to take into account research findings from these prerequisite topic areas, which may help explain why bonding was not one of the topics that was considered an early priority in this type of research. It may also be the case that researchers with a physics background would be more likely to look at physics topics, whilst many chemical education researchers might have reservations about investigating a topic so closely tied to physics concepts. (I teach both Physics and Chemistry to A level, perhaps partly explaining my interest in this topic.)
§1.4: Assumptions about learning
In order to proceed with an enquiry into learning of chemistry it is necessary to make some axiomatic assumptions about the learning process. Two central ideas I will use are that of cognitive structure, and learning impediments.
§1.4.1: Cognitive structure
Ausubel and Robinson define cognitive structure as "the facts, concepts, propositions, theories, and raw perceptual data that the learner has available to him at any point in time" (1969, p.51), although it might be suggested that this is actually a description of the contents of cognitive structure. When cognitive structure has been considered the knowledge someone possesses and the manner in which it is arranged it has been considered "ill-defined" (White, 1985, p.51), but the inclusion of reference to the arrangement of knowledge usefully augments Ausubel and Robinson's version. White's point was that we have very little knowledge about the appropriate 'units' or 'elements' in which to discuss 'knowledge' as held in cognitive structure, nor
what exactly we mean by its arrangement. We may have much knowledge about memory function from psychology, and some detailed information about brain physiology – but we have a very limited understanding of how our notions relate to our neurons. For the purposes of this present thesis the following composite definition will be used:
cognitive structure:
the facts, concepts, propositions, theories, and raw perceptual data that the learner has available to her at any point in time, and the manner in which it is arranged.
For present purposes then I will make the following assumptions, that I believe will be considered reasonable:
- that concepts are in some way 'stored' or represented in a learner's brain,
- and that there is some form of organisation of these representations (i.e., we accept the existence of cognitive structure);
- that therefore the notion of two concepts being more or less closely linked, connected or integrated in cognitive structure is a meaningful and sensible one;
- that we do not have direct access to a learner's cognitive structure;
- that a learner's behaviour (statements, responses to questions etc.) may be considered to reflect aspects of his or her cognitive structure;
- that we may construct models to represent cognitive structure in terms such as the various conceptions that a learner holds, and how they appear to be inter-related;
- that the utility of such models may be judged in terms of the extent to which they are consistent with, and may be used to organise and explain, the learner's behaviour (statements, responses to questions etc.)
§1.5: Learning impediments
From a teacher's viewpoint intended learning may fail to occur for a range of reasons, including a student not being able to hear the teacher, or not being able to read the board, or not listening to instruction. Although issues of classroom organisation, student motivation, and so forth are important in managing effective learning, they are outside the scope of this present study.
My context is students who are present in class, and motivated to learn, and able to see and hear the teacher's presentation. When intended learning does not occur in such a context the research agenda may concern such issues as effective communication, shared meanings and misunderstandings. In this context I am going to refer to there being 'learning impediments', although this term is not used
in the same sense of the learner having special education needs, or some deep psychological 'learning block' that interferes with learning in general (Bruner, 1979 {1962} , p.12). Rather these impediments will be conceptualised in terms of the intended learner's cognitive structure, and its relation to the material presented, but this does not imply that there is any sense in which the failure to learn is assumed to be the 'fault' of the learner.
I am using the term 'learning impediment' to mean some aspect of existing cognitive structure which interferes with the effective learning of material during science teaching. The term 'impediment' is thus used is a similar sense to 'barrier', i.e. as an obstruction, as something that acts as a 'mental block' to effective learning.
§1.5.1: A possible typology of learning impediments
I am going to suggest that – for my present purposes at least – such learning impedimenta may be divided into categories according to their pedagogic implications. The first distinction I wish to draw is between what I will call null learning impediments, and substantive learning impediments.
§1.5.2: Null learning impediments
A null learning impediment describes the situation where meaningful learning (§2.2.5) does not take place because the learner does not make a connection between the presented material and existing knowledge.
It may be that relevant material is held in cognitive structure, but that the learner does not appreciate its relevance, so the new material is stored as an unrelated fragment of knowledge. I will describe this case as a fragmentation learning impediment. If this is diagnosed the teacher may act in this situation to make connections explicit.
Alternatively there may be a deficiency in cognitive structure, in that appropriate 'prerequisite learning' may not have taken place – that is the 'jump' between the existing structure and the 'target' structure is too large for the new material to be assimilated in one 'step'. For example a student on an advanced course may not have covered the expected material in her elementary classes for some reason. I will refer to this as a deficiency learning impediment. In this situation remedial teaching is required.
A slightly different response is required where the material to be learnt is so highly abstract that there is no suitable prerequisite knowledge in the usual sense. Here the 'gap' must be 'bridged' through providing new experience on which to base learning, or through the use of analogies with familiar and more concrete situations (c.f. §2.3.10).
§1.5.3: Substantive learning impediments
As opposed to null learning impediments, substantive learning impediments are not caused by the absence of material perceived as relevant in existing cognitive structure, but in a sense are due to its presence.
In this situation the learner already has knowledge that is recognised as related to the new material being presented. However, the intended learning does not take place because the new material is seen to be inconsistent with the existing knowledge, or is seen to be related to existing cognitive structure in some inappropriate way. There are several possible outcomes here (c.f. §2.3.4):
i) perhaps no learning takes place, i.e. there is no substantial consequent change in cognitive structure. (It is unlikely that any experience would leave someone completely unchanged, and it might be expected that any exposure to teaching would lead to some shift in cognitive structure. However we will assume that in some cases the changes may be considered as trivial, in the sense of being very small changes, or peripheral, in the sense of not involving changes close to the 'target', and therefore negligible.)
ii) alternatively the new material is used to develop the existing conceptual framework, but in order to maintain consistency the meaning of the presented information is changed as it is reinterpreted by the learner;
iii) learning takes place, but in order to avoid contradiction, the new material is not associated with the intended framework of ideas, but is connected elsewhere in cognitive structure. (Ultimately all knowledge that is held in cognitive structure is connected, but I will assume that such connection may be so indirect in some cases that for most purposes the knowledge fragments are not perceived as related.) This will lead to fragmented learning.
In order to avoid such outcomes the teacher needs to help the learner 'debug' the existing cognitive structure, and this process has received a lot of attention in the constructivist science education literature. This requires both the diagnosis of alternative conceptions and strategies for bringing about conceptual change (see chapter 2, especially §2.10).
It is suggested here that to a first approximation substantive learning impediments may be considered as ontological or epistemological – although this distinction perhaps has less to do with their ultimate status than how the teaching profession should best avoid them.
§1.5.4: Ontological learning impediments
There has been much research into children's intuitive ideas about how the world is (see chapter 2). For example Ogborn has been involved with research which examines the categories which learners tend to use to think about the world, (Mariani and Ogborn, 1991) and with Bliss has described what they call a common- sense theory of motion (Bliss and Ogborn, 1993).
The term intuitive may seem to suggest that we are in some sense concerned with a priori knowledge, such as Kantian categories that are reached by pure thought alone (e.g. Russell, 1961). It does seems likely that some aspects of the structure of the human brain predispose us to think along certain lines. In former times many would have put this down to an act of special creation: that is, our minds reflect our creator and resonate with the rest of His creation. A more contemporary explanation might suggest that brain evolution has been constrained by physical law, and has been contingent on our environment. For example there has been research into the so-called natural kind categories that are believed to be recognised across cultures (e.g. Gelman and Markman, 1986). If there is survival advantage in having a brain that predisposes one to recognise such categories as fish (found in water, usually edible), trees (useful for hiding, often have edible parts) or large, sharp toothed carnivores (caution recommended) it is understandable such brain structure has evolved. (For such purposes the subtleties of scientific taxonomy may have less utility value, so that in general spiders may be categorised with 'insects', but not classed as 'animals'.)
Whatever predispositions there may be, actual concept development requires experience of the world. So our beliefs about the way the world is are a product of our experiences as processed through brains which have evolved according to physical laws, and contingent on the environment in which they co-evolved. As those experiences include social interactions, which in turn include more or less formal 'teaching' events, there can be no absolute division between the 'intuitive' and the 'taught', or between 'common-sense' and 'common knowledge'.
It is likely that some of our assumptions about the way the world is are developed early in life, before language is attained, and operate largely at a tacit level – as opposed to the easily verbalised 'alternative conceptions' that are normally elicited as simple statements representing propositional knowledge. These tacit understandings may have a wide influence on thinking, perhaps operating as
regulators as new understanding is constructed. The term Gestalts has been used to describe these tacit assumptions (Anderson 1986, see §2.4.4).
§1.5.5: Epistemological learning impediments
On the other hand, it may be useful to draw a distinction between learning impediments which may be seen to be largely caused by the deliberate prior teaching of specific material (§1.3.2), and those acquired through more nebulous experience. Research tells us that once established alternative conceptions may often be very stable, and may act as significant impediments to subsequent intended learning (§2.3.4). It is argued here that such alternative ideas may be equally effective as learning impediments, whether they are a learner's 'intuitive theory' or a 'misconception' of taught ideas. Yet the latter category of learning impediment may be avoidable in the future by appropriate changes to curriculum, text books and teaching schemes. It would therefore seem that if such impediments are identified, effort should be made to rethink our teaching approaches to see if we can avoid them in the future. I will refer to such substantial learning impediments as epistemological learning impediments.
So an epistemological learning impediment is an aspect of cognitive structure derived from deliberate formal instruction, yet which impedes subsequent learning. There has been much research into what I am calling ontological learning impediments – alternative conceptions and frameworks developed prior to formal tuition. The lack of direct personal experience, the complex and abstract nature of theory, and the reliance on prerequisite learning could make chemical topics such as bonding fertile areas for researchers to uncover epistemological learning impediments.
§1.5.6: Pedagogic consequences of learning impediments
The four categories of learning impediment, and the ways that it is envisaged teachers should work to overcome them, are summarised in the table below:
| type of learning impediment | nature of impediment | action required |
| deficiency impediment | no relevant material held in existing cognitive structure | remedial teaching of prerequisite learning (if available), or restructuring of material with bridging analogies etc. |
| fragmentation impediment | learner does not see relevance of material held in cognitive structure to presented material | teacher should make connections between existing knowledge and new material explicit |
| ontological impediment | presented material inconsistent with intuitive ideas about the world held in cognitive structure | make learner's ideas explicit, and challenge them where appropriate |
| epistemological impediment | presented material inconsistent with ideas in cognitive structure deriving from prior teaching | for individual learner: treat as ontological impediment; for future: re-think teaching of topic – order of presentation of ideas, manner of presentation, etc. |
§1.6:Bachelard’s epistemological obstacles
The term epistemological learning impediment is similar to the French philosopher Bachelard's phrase 'epistemological obstacle'. Bachelard had taught physics and chemistry at secondary level (Souque, 1988, p.9), and saw his first duty to his students to be to shake their preconceptions (Goldhammer, 1984, p.xxiv). Bachelard wrote as long ago as 1938 that "the adolescent enters the physics class with pre- conceived ideas", and that there was a need to "demolish the obstacles accumulated by daily experience" before desired learning could take place (quoted by Souque, 1988, p.9). Bachelard labelled these obstacles as 'epistemological', and by analysing historical scientific texts he identified a number of classes of such obstacles.
Souque lists five of Bachelard's categories of epistemological obstacles which relate to science teaching: immediate experience, generalising knowledge, the verbal obstacle, the animistic obstacle, and the obstacle of quantitative knowledge (pp. 9-12). These 'obstacles' may be considered to be examples of what I have called substantive learning impediments – aspects of cognitive structure that act as impediments to intended learning. Four of these categories, immediate experience, a tendency to generalise, a tendency to animism, and a tendency to allow quantification to stand for explanation, are related to my category of ontological learning impediments, as they are ways of responding to the world which are not deliberately taught. Bachelard's verbal obstacle relates to the way that naming a phenomenon may provide a convenient label which stands in place of an explanation. This category also includes analogies and metaphors used in science, which may again stand in place of a deeper understanding. This type of obstacle is
closer to my category of an epistemological learning impediment, particularly as Bachelard drew a distinction between the scientific mind – where a theory is understood, and then an analogy drawn – and the prescientific mind – where it is the analogy that is understood before the theory. This may be seen as a parallel for teaching analogies with the teacher and student representing the scientific and prescientific minds (c.f. §2.3.9 and §12.4.4).
A related aspect of Bachelard's work was his concept of an epistemological profile. Bachelard studied how scientific concepts had changed over time, and in particular how the historical development of a concept related to philosophical positions of varying sophistication (animism, realism, positivism, rationalism, and what Bachelard termed 'surrationalism' or complex rationalism and dialectical rationalism, Bachelard, 1968 {1940} , p.15). Bachelard thought that this sequence of philosophical positions was found across different scientific concepts – he wrote that "the direction of epistemological evolution is clear and constant: the evolution of a particular piece of knowledge moves towards rational coherence" (p.17). As he considered scientific progress to be the "one form of progress which is beyond argument", this sequence could represent "philosophical progress in scientific notions" (p.17). In practice different branches of science were at different degrees of "philosophical maturity", and so Bachelard characterised the philosophy of science as being "dispersed" or "distributed" (pp.10-11), and referred to "a multiplicity of philosophical explanations of science" (p.17). Bachelard believed that some physicists recognised the dialectical nature of their work. So, for example, he described (1984 {1934} , p.86) how Heisenberg included in the same book "two curiously antagonistic chapters": a critique of particle theory in terms of wave theory, alongside a critique of wave theory in terms of particle theory. Chemists, however, appeared to believe that the substances and reactions they studied were 'given' in nature rather than being the outcome of a dialogue with nature. Accordingly, Bachelard described chemistry as being "the elected domain of realists, of materialists, of anti-metaphysicians" (1968 {1940} , p.44).
Bachelard believed that although the concepts of formal public science progressed over time, in practice individual scientists did not exclusively apply the most sophisticated version of the concept. Rather the concept in the mind of the individual included aspects of the various historical versions, what he described as "…this plurality of meanings attached to one and the same concept…" (p.21). Bachelard demonstrated this by producing epistemological profiles – reproduced below – for his own conceptualisation of mass (p.36) and energy (p.38).
Bachelard's personal epistemological profile for 'mass' (redrawn from Bachelard, 1968 {1940} , p.36.)
Bachelard's personal epistemological profile for 'energy' (redrawn from Bachelard, 1968 {1940} , p.38.)
For Bachelard the epistemological profile represents evidence of epistemological obstacles, that have acted historically, as the profile "bears the marks of the obstacles which a culture has had to surmount" (p.43). He thought that the earlier philosophical positions acted as obstacles to progress (p.37). As one of his translator's commented, Bachelard believed that
"the prehistory of science (even its mythology), to the extent that it persisted in the structure of the human mind, needed to be exorcised – the Aristotelian, the Euclidian, the Newtonian, even the criticist spirit of Kant, leave structural layers in the human mind akin to the geological strata of the earth, and we need knowledge about these layers, self- knowledge and self-correction, before we can proceed."
Waterston, 1968, p.xi.
§1.7: The notion of progression in learning chemistry
I believe the three factors discussed above (§1.3) contribute to the limited amount of previous research into students' understanding of chemical bonding in the literature. These factors have therefore been taken into account in my own conceptualisation of, and approach to, the research problem. The nature of chemical concepts has been taken into account in my own thinking about how to define progression in learning chemistry. It is suggested that it is appropriate to think in terms of the learner developing a conceptual toolkit.
§1.7.1: Manifold models: the nature of some chemical concepts.
There are many studies in the literature that have examined learners' ideas in science by interviewing a range of individuals on one occasion each, comparing the learner's statements with accepted scientific ideas, and then listed and/or categorised the range of alternative ideas elicited.
For example Watts' analysis of interview data led to a set of frameworks that he constructed to make sense of learner's ideas about forces (1983a) and energy (1983b). As a physicist and experienced science teacher Watts had his own 'teacher's science' version of these concepts to act as a benchmark, by which he could judge whether learner's ideas were 'alternative'. (The use of descriptors such as scientists' science, teacher's science and children's science has been suggested by Gilbert, Osborne and Fensham (1982) to distinguish the status of various science knowledge claims, §2.3.2). Further, as his study was not concerned with progression in individuals' understanding, Watts did not need to evaluate the relative merits of the various alternative frameworks uncovered.
It was suggested above that some concepts in chemistry may need to be considered in a different manner to physics notions such as force. It is generally agreed that there is a scientist's science concept of force even if the extent to which learner's ideas are expected to match the scientist's science varies considerably with educational level. I would argue that some key chemical concepts are more complex because the scientist's science concept is actually an amalgam of distinct and inconsistent models of variable applicability. The notion of matching scientists' science becomes more problematic as it depends on specific context as well as educational level.
Driver has commented on the tendency to use a range of models of varying degrees of complexity in science,
"In many areas of science, phenomena can be interpreted at a range of levels of sophistication, all of which are in some sense useful. … [A] model [for electric current] is only 'better' than the previous one in that it accounts for a greater range of phenomena. A similar shift in the level of theoretical sophistication is encountered in several other topics, for example, in chemical bonding, the wave properties of light, inheritance and the molecular-kinetic theory of heat"
Driver, 1983, p.80, emphasis added
Driver here seems to be largely discussing models in curriculum science or teachers' science. Although the fluid flow model of electricity has been widely used as a teaching model, it has little currency in physics research, i.e. in scientists' science. In physics, electricity is understood in terms of a unified theoretical framework, based on accepted fundamental principles.
It has been argued in the past that in principle chemistry could be explained in terms of physics (§1.3.1). Scerri (1993) has considered the question of whether chemistry can be considered a reduced science – that is: can the problems of chemistry be reduced to applications of the principles of physics? Scerri points out that although in principle chemistry can be explained in terms of quantum mechanics: in practice the calculations are problematic in all but the most simple systems. That is, in practice, chemistry is something other than a branch of applied physics. Brock makes the same point when he claims that theoretical chemistry is "a quirky empirical science based upon a Schrödinger equation that can hardly ever be solved" (1992, p.505).
Zavaleta (1988) has noted how chemical 'facts' can not be seen in isolation from the theoretical framework in which they are discussed: he discusses several examples from the conceptual history of bonding theory, where "the meaning of a fact is inseparable from preconceived attitudes toward that fact" (p.680). Whilst this observation would apply to the history of all branches of science, where various paradigm shifts (Kuhn, 1970 {1962} ) have occurred, in the case of chemical bonding Zavaleta has pointed out that chemists still currently use apparently incompatible theories to explain bonding, choosing the theory which is most successful for explaining the phenomenon in each case (p.677). He reports that the best method depends on the compound being studied (p.680). He concludes that,
"It seems impossible to teach chemistry without misleading ourselves and our students to some, perhaps even a great extent. … The conceptual history of bonding suggests that even the magnitudes of "accepted" facts do not exist apart from theoretical assumptions."
Zavaleta, 1988, p.680
Benfey has also argued that chemists can not understand the empirical data available in terms of a single theoretical framework,
"sometimes [chemists] must live with two irreconcilable but complementary facts or theories because giving up one or the other member of such a pair would be false to our full awareness of the mystery of the natural world"
Benfey, 1982, p.398
The lack of a single unifying theoretical principle for chemistry leads to a profusion of models. Car (1984) suggests that in chemistry 'model confusion' is likely to be a more significant problem for learners than the existence of 'preconceptions',
"students' difficulties in this area may be more usefully perceived in terms of confusion about the models used in teaching the concept rather than as a conflict between preconceptions and the scientific view"
Carr, 1984, p.97
Although his comments were based a consideration of the topic of acids and bases, he recommended further research in other chemical topics (Carr, 1984, p.103). As examples he posed the questions (p.103),
- are some problems about ions a result of carrying Daltonian and Newtonian models of atoms beyond their utility – since in those models atoms are unbreakable?
- are covalent bonding ideas served at all well by the Bohr model of the atom?
This present research may be seen – in part – as developing Carr's research programme into the curriculum area of chemical bonding.
Driver's comments above alert us to the succession of models through which learners acquire more sophisticated 'versions' of concepts such as 'electrical current', and suggest that progression in science learning could be understood in terms of the acquisition and mastery of successive models. My own analysis of the chemical bond concept (presented in appendix 4) led me to conclude that although there is a series of models of increasing sophistication, these are used as alternatives by chemists, rather than being seen as a sequential progression of teaching models which leads to the current scientists' science model of the chemical bond. This can be understood in terms of Scerri's observation that chemistry is not (yet) able to be reduced to physics. The expectation then is that Carr's 'model confusion in chemistry' is likely to extend beyond acid-base theory to topics such as the chemical bond.
§1.7.2: The toolbox analogy
In terms of my own study, modelling progression in student understanding of the chemical bond is informed by the alternative acceptable models for bonding that are available.
The professional chemist, who has acquired and mastered the most sophisticated chemical bonding ideas, may nevertheless on occasions use a much more simplistic and limited concept of the chemical bond, because it seems more appropriate in some contexts. It would therefore be inappropriate to judge that a student lacks a more sophisticated perspective on bonding, simply because in the context of a certain research probe he or she selects to respond in terms of a more basic set of ideas.
To allow for this potential difficulty, I suggest that it is appropriate to conceptualise students' thinking in terms of the use of a toolbox of chemical concepts. The difference between the 'expert' chemist and the relatively 'naïve' student embarking on an A level course is that the novice does not have alternative strategies for when her G.C.S.E. (KS4) level understandings do not help explain the chemical data. As the student makes progress in the subject she will acquire more tools, and learn both how and when to apply them.
The G.C.S.E. 'graduate' has a 'toolbox' containing some useful chemical 'tools' to tackle a range of chemical 'jobs'. As students pass through an A level course they will continue to use these tools, but they will also meet many 'jobs' where their 'toolbox' does not provide them with a suitable instrument. The task of the teacher may be seen as to provide additional tools, and training in how and when the different tools should be used: a role which fits quite well with the idea of cognitive apprenticeship that has been discussed as a model for learning in science (§2.8.5). Some students will be more successful in acquiring the tools than others – success being measured not only in ownership of the tool (e.g. describing the rules of valence shell electron pair repulsion theory) but also in its appropriate use (e.g. explaining and predicting the shapes of simple molecules, but not trying to use it to explain patterns in ionisation energies – a job which requires a different tool). The practising chemist has a more extensive toolbox than the G.C.S.E. candidate, but still uses some of those same basic instruments. Different practising chemists carrywith them, and use, different toolkits – they will have acquired different tools over their careers, and even perhaps discarded some that are not appropriate for the jobs they undertake.
I argue that this approach is a very powerful one, as it avoids the incorrect idea that more sophisticated understanding 'replaces' more basic ideas: in chemistry this is not always true – the more sophisticated ideas often supplement and complement the more basic ones. The tools I am discussing are mental tools: rules, laws, heuristics, models, representations etc., they are tools from Popper's 'World 3' ("objective thought, especially products of the human mind", 1979, p.395), as are the chemical 'jobs' to be undertaken – explaining and predicting the properties and processes of nature. The phenomena to be explained are of 'World 1' (the "physical world", p.394): but our categories, and our explanations are mental constructions. As with other kinds of tools, these mental tools are not usually fully mastered at first acquaintance. In this research, an attempt was made to follow progression in terms of how and when a concept was used by a colearner.
In order to apply this analogy it is necessary to undertake an analysis of the topic area being studied. This task was undertaken early in the research, and the results are appended (as appendix 4). Appendix 5 presents a list of propositions that might represent expected prerequisite knowledge. In Appendix 6 the A level chemistry syllabus content most relevant to the concept of 'chemical bonding' is reproduced. In Appendix 4 the toolbox analogy is applied to the concept of chemical bonding. The likely extent of a successful learner's toolbox on entering A level study is presented, and then progression is considered in terms of how this toolbox might be extended and developed during an A level course. It should be emphasised that this analysis does not primarily derive from the research findings presented in chapters 6-11, but rather provides my own starting point for setting out on the analysis of my research data. In chapter 12 (§12.4) I will revisit this approach in the light of what was found out during the research.
§1.7.3: Overcoming learning impediments
A typology of possible learning impediments was presented above (§1.5). Progression in learning about the chemical bond would require such impedimenta to be overcome. Successful acquisition of the conceptual tools of curriculum science would require the learner to hold the appropriate prerequisite learning in conceptual structure, to realise the relevance of new ideas to the existing knowledge, and to avoid or overcome the interference of existing alternative conceptions – whether derived from intuitive notions or developed from earlier formal learning. This may be illustrated through the example of learning about the concept of the polar bond.
§1.7.4: The polar bond: an example of an A level chemistry concept
As an example to illustrate some of the points made above, consider the concept of a polar bond. This is not part of the 'toolkit' that my colearners brought to their A level studies (§11.6.2), but was part of the syllabus they were expected to study (appendix 6). It is a conceptual tool they are expected to acquire and be able to use.
In the examination syllabus (see appendix 6) this concept is listed with some related ideas (electronegativity; inductive effect; homolytic and heterolytic fission; nucleophilic and electrophilic attack respectively, on positive and negative centres in molecules).
A polar bond may be considered to be something intermediate between a covalent bond and an ionic bond. One way to model this is to use the simple idea of a covalent bond as a pair of electrons equally shared between two atoms, and to consider that in a polar bond the sharing is unequal. This may be conceptualised as the electron pair nearer one end of the bond, or with greater sophistication as an asymmetric electron density cloud. It is also possible to consider the polar bond as an ionic bond where the cation has polarised the electron cloud of the anion, as a resonance of the covalent and ionic forms, or as a molecular orbital which is asymmetrical between the two atoms due to the differences in the contributing atomic orbitals.
In chemistry bond polarity is said to be due to an electronegativity difference in the two atoms that are bonded. Electronegativity, in turn, can be related to the size of an atom, and its core charge (which is equal to the magnitude of the nuclear charge minus the number of shielding electrons).
The polar bond is clearly a concept that can be understood at a number of levels, of different sophistication, but all providing some insight. Understanding the polar bond assumes a knowledge of G.C.S.E. level chemistry (the covalent bond, the ionic bond, atomic structure in terms of charged particles, and electrons in shells), but is also related to other concepts such as electronegativity, core charge and orbitals that – like bond polarity itself – are also new to A level students. Understanding some aspects of the polar bond requires the learner to be familiar with some principles of quantum theory, which although actually a part of physics, are explicitly taught in A level chemistry (so the syllabus content in appendix 6 includes "elementary treatment of quantum numbers and atomic orbitals"). However, to make sense of some aspects of this content the learner also has to apply assumed prerequisite physics that may not be explicitly taught, in terms of basic electrostatics. The factors determining electronegativity of an element can be explained in Coulombic terms. The unequal sharing of the electron in a polar bond can be understood in terms of the equilibrium position reached when the electron pair is attracted to the two differently charged cores, but repelled by the other valence electrons. The notion of an electron pair itself requires the introduction of the idea of quantum-mechanical spin to explain why negatively charged electrons can be considered to pair.
Even from this brief discussion of one concept it is clear that progression in chemistry at this level requires the foundations of previous learning about chemistry and physics, the ability to switch between a range of models of varying levels of sophistication and abstraction, the ability to form chains of logical argument which work through various levels of explanation, and the acceptance of a theoretical structure where a range of – perhaps dimly understood – ideas are used to buttress one another.
The complexity of this concept suggests that whilst an individual lesson objective might be to introduce the idea of the polar bond, the desired understanding of the concept could only be a long term teaching goal: something to be developed though a careful process of gradual extension and reinforcement of learning. It also seems clear that in this example there is considerable scope for progress to be impeded. Consider the following hypothetical examples as an illustration:
- A learner who did not have assumed prerequisite knowledge about the electronic structure of the atom would not appreciate what was meant by the atomic core (a deficiency learning impediment).
- A learner who did not appreciate the relevance of electrostatic principles learnt in school physics might not apply them to this chemical context (a fragmentation learning impediment).
- A learner who accepted the division of chemical bonds into covalent and ionic as 'natural', reflecting a principle that nature exhibits dichotomies (perhaps such as metal/nonmetal; male/female; animal/ plant; matter/energy), might not be able to accept the polar bond as a meaningful category (an ontological learning impediment).
- A learner who applied the learnt idea that 'similar charges repel' to the electrons in a bond without modification might only be able to visualise the electron distribution in the bond as one electron at each end (an epistemological learning impediment).
§1.7.5: Learners’ ideas as learning impediments or cognitive resources
It is clear from what has gone before that in this research learners' ideas about chemistry are seen as potential impediments to progress in studying the subject. However, this is not meant to suggest that learners' alternative conceptions should necessarily be seen as problematic. In the literature in chapter 2 it will be suggested that meaningful learning can only take place when the learner can relate new material to existing knowledge (see §2.2.5) – otherwise there will be a null learning impediment. The learner's existing cognitive structure therefore acts as the resource base on which new understanding will develop. Research has suggested that a rich conceptualisation is an advantage in learning science (see §2.3.11). A learner's intuitive notions, or misconceptions of the teacher's words, or recollection of a simplified explanation given by an adult, or even knowledge of some folk wisdom, could all potentially act as either substantive learning impediments or the foundation for constructing an acceptable scientific understanding. The question of whether learners' alternative ideas should be considered as barriers or bridges in considered in the next chapter (§2.3.9).
§1.8: The longitudinal nature of this research
To recap then, this thesis investigates the development of A level students' understanding of the concept of the chemical bond. This is one of the key concepts which is fundamental to the study of chemistry, yet there has only been a limited amount of research into the learning of this curriculum area. The present work addresses this deficiency, and takes into account the factors identified as possible reasons for the previous lack of attention.
Much of the early research into learners' ideas in science has been characterised as 'fishing expeditions' or 'butterfly collecting' (Watts 1988, Black, 1989). Such work leads to catalogues of learner's notions, but does little to explore the richness of learners' cognitive structures, or the manner in which thinking develops over time. In chemistry much of the work that has been carried out is of this form (Garnett et al., 1995). It is clear from my characterisation of chemistry concepts above that the present thesis describes an attempt to move beyond this.
The discussion of the concept of the polar bond (§1.7.4.) illustrates how concept learning at this level needs to be studied over a time-scale of months (or even longer, §12.4.2). A number of commentators have recognised that longitudinal studies are needed that follow the subtleties of individual's thinking over extended periods to examine issues of concept stability and development (Black, 1989, pp.3-4; Driver and Erickson, 1983, p.54; Driver, 1989, p.484; Gilbert and Watts, 1983, p.87; Howe, 1996, p.48;Watts, 1988, p.75).
The present thesis is based around a longitudinal research design where a limited number of learners were interviewed in depth over extended periods of time, with the aim of following development in understanding. These learners were volunteers, and were students of the researcher. This allowed a strong rapport to be developed, as the research was undertaken within the context of ongoing teacher-student relationships. This has a number of consequences for the research (§4.10.3). It brings advantages as I was able to bring insights from the classroom into the research sessions, and I was able to triangulate the findings from interviews against student course work (§4.9).
This approach also has other consequences for the research. For one thing, the teacher-researcher has responsibilities as a teacher. I had ethical responsibilities to my students to use the research interviews for their benefit: that is to provide them with useful feedback after research sessions. Indeed the students were conceptualised as colearners (§4.3.2) in the research. It would not have been appropriate for me to withhold feedback about, say, a significant misconception uncovered to find out whether it would be 'corrected' over time without my intervention (§4.10.3). However, it is not unusual in studies with an 'action-research' flavour for the desire to take action (i.e. improve educational practice) to compromise the study as 'pure' research (§4.1.2). In the present study the model produced in chapter 6 aims to identify factors which are significant in student progression. Had the intention been to produce some normative model of the average rate of student progress then the interventionist nature of the present research would have been a problem – but so would the small sample size, and the limited educational context. However, as is explained in more detail in chapter 4, the intention has been to develop grounded theory (§4.4). This theory – the model presented in chapter 6 and discussed in chapter 12 – is intended to be suitable for traditional hypothetico-deductive testing, but such testing is largely beyond the scope of the present work (although the feasibility of such testing is demonstrated in appendices 2 and 3).
A related issue is the question to which learning is something that occurs within a learner, or 'between' a learner and a tutor or peer. The influence of Vygotsky's ideas (§2.2.2), and the modelling of learning as a kind of cognitive apprenticeship (§2.8.5), suggest that any study which focuses on the what the learner can do in isolation ignores the normal context of learning (§4.10.4). From such a perspective the other minds with whom the learner interacts are key variables in the learning process, and the involvement of a teacher in a learning interaction is equally a necessary complication regardless of whether the teacher is also the researcher.
So the present study, then, develops a model of significant aspects in student learning about the chemical bond, based on detailed study of a limited number of learners in a particular institutional context, and taught by particular teachers, one of whom is also the researcher. The study is therefore undertaken in an idiographic tradition (§4.1.1) and this is reflected in the decision to present two detailed case studies of individual learners as part of the findings (i.e. chapters 7 and 8). The question of the generalisability of the findings outside of the specific context in which they were developed is considered in chapter 4 (§4.4, §4.10.5), and appendices 2 and 3 demonstrate the feasibility of testing the model against A level chemistry students in general.
§1.9: The structure of this thesis
Following this introductory chapter, the remainder of this thesis is presented in eleven further chapters.
Chapter 2 presents an account of the field of constructivist science education research in which this present study is located. Chapter 3 reviews what was already known about student learning of chemical bonding. This chapter also considers studies into learning about the areas of prerequisite knowledge considered to be significant to avoid deficiency learning impediments. Chapter 4 explains the overall choice of methodology used in this study, and chapter 5 gives details of the data collection and analysis techniques used.
Chapters 6-11 present the findings of the research. Chapter 6 acts as an 'advance organiser' for readers, setting out the overall results of the study. Chapters 7 and 8 present case studies of individual learners, concentrating on their progression in understanding the chemical bond concept over time. Chapters 9 through 11 consider the three main themes which were identified through the data analysis as being most pertinent to developing understanding of chemical bonding.
Finally, chapter 12 discusses the findings of the study to consider the extent to which the initial research agenda set out in the present chapter has been addressed. In that final chapter suggestions for further research are made, and recommendations for changing the teaching of chemistry are presented.
