Robert Bucat

Department of Chemistry, The University of Western Australia, Australia



High quality teaching demands more than both good content knowledge and good pedagogical knowledge: it requires a consideration of how specific characteristics of the content might influence one’s pedagogy, and vice versa.  The term pedagogical content knowledge refers to knowledge derived from the interaction between pedagogical beliefs and characteristics of the content in order to decide how a particular topic might be presented for optimal “learnability”.  To use an example in our context, pedagogical content knowledge refers not to knowledge about stereochemistry, but to knowledge about the teaching and learning of stereochemistry.  Perhaps reflection upon, and research into, pedagogical content knowledge will be the next major step in the evolution of chemical education.

Attention is given to an analysis of pedagogical content knowledge specific to a particular topic in chemistry, and how this might influence the teaching of that topic.  It is argued that developing pedagogical content knowledge about topic X constitutes the creation of new knowledge different from, but equally as worthy as, research knowledge about topic X.  Recognition of this might enhance the status of good chemistry teachers.



It is my perception that the chemical education enterprise has traversed two distinct phases over recent decades: a reflective phase and, more latterly, a research-based phase.  Currently it seems not sure of its identity and where it should go.  If we accept a distinction between pure and applied in chemistry research, then I suggest by analogy that we have been intensively engaged in pure chemical education research in recent years.  Perhaps the time is ripe to engage in a line of applied research, involving both reflective analysis and empirical studies, the findings of which will be immediately useful to the teacher at both secondary and tertiary levels.  When we have bridged the gap between general educational theoretical advances, and specific knowledge that can assist us to teach about chemical equilibrium (for example), then perhaps chemical education research will begin to make more impact on the practice of teaching chemistry.  This applied research will necessarily involve collaboration between chemists and teachers, along with science education researchers.


Chemical education, Stage 1: Reflection about “What to teach?”

Until about 1975, there was very little experimental research concerning the chemistry curriculum. Chemical education was concerned almost exclusively with either (i) advances in the subject matter, or (ii) the question “What should be included in the chemistry curriculum?”  Almost every issue of the Journal of Chemical Education contained articles related to this latter question. The powerful influences in chemical education were position papers published by highly respected academic chemists.  These papers were based on opinion and judgement derived, not from empirical findings, but from reflection grounded in experience and wisdom.  These position papers seem to suggest that the “answer” for chemical education lay in the selection or design of the “right” curriculum, as defined by the choice of subject matter.  In most (but not all) of these discussions, it seems as though the curriculum is perceived as an interaction between teacher and subject matter.  It was as though the students were regarded as part of the fixtures (or the teacher’s context?) in the teaching task - especially at the tertiary level.


Chemical education, Stage 2: Experimental research into “What is learned?”

From about 1975 we have seen a dramatic change in the nature of the science education endeavour.  Although we still need to, and do, ask the question “What should be taught?” there has been an enormous investment of energy in experimental research into the question “What is learned?”  The world has been tipped upside down!  The focus has shifted from the curriculum (the syllabus to be taught) to the student, reflection has given way to experimental investigation, and those asking the questions are mostly “science educators” rather than scientists.  In a few instances around the world, people engaged in this research are in Chemistry Departments, doing chemistry and working with chemists.


Probing students’ understandings became a science education “industry” and there is at least one book (White & Gunstone, 1992) describing methods for going about this very difficult task.  Much of this research is described as “misconceptions research”: its purpose has been to identify inadequacies in students’ understandings, in comparison with what the teachers might have hoped for.  Garnett et al. (1995) and Nakhleh (1992) have published comprehensive reviews of the findings of “misconceptions research” in chemistry education.  There are two stunning outcomes from the very many “misconceptions research” studies that have been conducted.  Firstly, many of the misconceptions that have been identified are common to students of all countries, and at a variety of levels of education, including many students scoring well in formal written examinations.  Secondly, many misconceptions are extraordinarily resistant to change.  These findings have led to questioning of the “transmission” (teaching is telling and learning is remembering) mode of teaching.  The evidence supports the view that formal learning often constitutes little more than an ability to reproduce symbols and words and to apply algorithms.  And so began (or, perhaps better, re-convened) a period of reflection upon how people learn. If transmission of knowledge by telling is not a very effective way of teaching and learning, why isn’t it?  What is a better way?  This is a story in itself and is not the issue here, but perhaps I might refer to two lines of thinking.


Firstly, we have had ten or fifteen years on top of a wave called “constructivist” theory.  The essence of constructivism is perhaps best summarised as: “Knowledge is constructed in [not absorbed by] the mind of the learner” (Bodner, 1986).  By and large, a “constructivist” teacher will value and take into account the students’ prior understandings, will look for ways to develop linkages between new knowledge and pre-existing sound student knowledge, and might try to create situations such that the students need to grapple with challenging ideas.  Secondly, an “Information Processing model” (Johnstone, 1997) has at its heart (i) a selective filtration process, influenced by what we already know, for choosing which of the incoming sensory signals we attend to, and (ii) an interaction in a limited capacity “working memory space” between selected new information and prior knowledge.


Where are we at?

For researchers, the belief that teachers’ conceptual understandings can be transferred in 1: 1 correspondence to students through “teaching by telling” is dead and buried.  But it must be said that praxis consistent with the transmission model is still alive and kicking.  The research-practice gap has not been bridged.  Here we are in 1998 with an encyclopedic collection of student “misconceptions” and an enhanced knowledge of the conditions for effective learning, based upon which a range of student-centred teaching methodologies, such as cooperative learning, have become fashionable.  Mitchell and Mitchell (1992) have published a valuable typology of classroom strategies designed to provoke conceptual struggle, and Bucat and Shand (1996) have developed examples of these in a few chemistry topics.


But there is a partial vacuum.  We have new generic ideas about teaching, but little guidance as to how each teacher might apply these to the teaching of particular chemistry topics.  We have a multitude of research publications concerned with identification of misconceptions, but usually no more than bland, general statements about preventative or curative actions – such as “We must find out what the students know at the start and use that as the basis for our teaching.”  We have educational researchers and teachers working in isolation from each other - except in a few cases of teachers involved in “action research”.  We have science education researchers and academic chemists by and large distant from each other and even exhibiting some disdain for each other.  And, perhaps as a consequence of all of the above, educational research has had little impact on science teaching except in particular instances.  Finally, it seems to me that many people involved in science education research are asking “Where to now?”


Chemical education – the future: Pedagogical content knowledge.

Science education research has important messages for the teaching and learning of chemistry, but I wonder if the focus is not too much on advancement, rather than application, of generic educational theories.  Commenting on criteria used for evaluation of teaching in the 1980s, Shulman (1986) asked “Where did the subject matter go?  What happened to the content?”  Of course we should attempt to advance educational theory, in the same way that any other discipline does “pure research”.  But surely advances in theory of a discipline have only one purpose: to reflect back on, and improve, the practice of that discipline.  Is the time ripe to think through what we now know about student learning, in conjunction with analysis of what it means to understand particular concepts in science, to generate useful pedagogical practices specifically tailored for each concept?  And then to assess, through research, the effectiveness of these practices?  This would correspond with the notion of “applied research” in the science disciplines.


A clue to the future is in the following excerpt (Fensham & Kass, 1988):

There are two primary and interacting sources of events in chemistry instruction that can lead to inconsistency, or discrepancy for its learners ..... .  The first is the science of chemistry itself.  The second is the teaching of chemistry. ...., .  The interaction between these two sources is obvious, but it is often ignored in the education of chemistry teachers.

Perhaps a productive path for us to travel is what Shulman (1986) has labelled pedagogical content knowledge (PCK).  While content knowledge refers to one’s understanding of the subject matter, and pedagogical knowledge refers to one’s understanding of teaching and learning processes independent of subject matter, pedagogical content knowledge refers to knowledge about the teaching and learning of particular subject matter, taking into account its particular learning demands.  The rationale for doing this is aptly put by Geddis (1993):

The outstanding teacher is not simply a ‘teacher’, but rather a ‘history teacher’, a ‘chemistry teacher’, or an ‘English teacher’.  While in some sense there are generic teaching skills, many of the pedagogical skills of the outstanding teacher are content-specific.  Beginning teachers need to learn not just ‘how to teach’, but rather ‘how to teach electricity’, how to teach world history’, or ‘how to teach fractions’. (p. 675)

Or, ‘how to teach stoichiometry’, or ‘how to teach chemical equilibrium’, or ‘how to teach stereochemistry”.  Obviously the demands of learning about stoichiometry are different from the demands of learning about stereochemistry.  Good teachers analyse (with varying degrees of consciousness) the various sorts of content-specific demands.


Each chemistry teacher has a unique knowledge of chemistry.  We cannot hope to transmit to the students a duplicate of this knowledge.  The teacher’s job is to re-package and re-present his/her knowledge in such a way that gives the students some hope of achieving the understandings that we hope for.  The re-packaging task will depend upon the nature of the subject matter.  And so we teachers have to come to know the subject matter, not only for itself, but also in terms of its teachability and learnability.  This task has been conceptualised (Shulman, 1986) as “transformation of subject-matter knowledge into forms accessible to the students”. Geddis (1993) points out:

In order to be able to transform subject matter content knowledge into a form accessible to students, teachers need to know a multitude of particular things about the content that are relevant to its teachability. (p. 676)  Developing ways to do this is indeed the creation of new knowledge of a type that characterises the good teacher and is part of his/her professional skill.  The requirement for teachers to invent this new knowledge should be recognised.  The highest levels of teaching ability demand more than just common sense.


What constitutes pedagogical content knowledge?

It seems to me that a prerequisite to generating PCK about a given topic is an analysis of the “sorts of knowing” that will enrich one’s understanding of that topic.  In relation to single-component phase diagrams, West and Fensham (1979) have identified a highly interlinked relationship amongst propositional knowledge, intellectual skills and images of observable phenomena.  Let’s consider just a few ‘sorts of knowing’, other than propositional knowledge and intellectual skills, in relation to the topic of chemical equilibrium (just to provide a concrete example).  Awareness of these constitutes PCK:

1.         White (1988, p.31) has remarked on the importance of images of observed phenomena and experiences, to which he attributes the label episodes.  What episodes might enrich a student’s understanding of chemical equilibrium? In what senses could each episode lead to richer understanding?


2.         We have become increasingly aware, as discussed by Johnstone (1991), of the learning difficulty presented by the need to consciously switch between observable macroscopic phenomena and images of the sub-microscopic molecular level – which we use to rationalise macroscopic behaviour. Bent (1984) has written in fascinating terms about “seeing through the eyes of a chemist”.  Ben-Zvi et al. (1987) have demonstrated the importance of also recognising the distinction between single-molecule sub-microscopic imagery (eg, for dipole moments) and multiple-particle images (eg, for limiting-reagent stoichiometry).  What are the characteristics of “good” mental imagery for the topic of chemical equilibrium?  Could some mental models have features which would handicap quality learning?


3.         One component of richness of understanding chemistry is an ability to properly use and interpret the language that chemists use (Cassels & Johnstone, 1983; Sutton, 1992).  Categories of language that can provide difficulties for meaningful communication include (i) chemical symbolism, such as symbols, formulas and equations, (ii) mathematical statements, (iii) technical jargon peculiar to the field, (iv) words which are also used in everyday settings, perhaps with different meanings, and (v) oddities, that might be called chemical colloquialism.  The topic of chemical equilibrium is loaded with linguistic traps for students.  What are these potential traps?  What strategies might be used to avoid mis-communication, or to avoid rote uncomprehending use of the language, in the topic of chemical equilbrium?


4.         The more easily one can operate with a variety of models, or multiple levels of explanation, the richer is one’s understanding of a subject. Carr (1984) has pointed out that multiple models of acids and bases can be a source of confusion for students.  Are there multiple levels of explanation applicable to the topic of chemical equilibrium?  What are the inclusivity/exclusivity relationships amongst them?  What are the limitations of applicability of each? Which are appropriate for your students?  Why?


5.         West and Fensham (1979) have suggested that awareness of the linkages between ideas, skills and episodes is important to quality learning of chemistry.  We might add mental images to this list.  And we might also argue that recognition of the (extrinsic) links between the topic under study and other chemistry topics can enrich our understanding.  What intrinsic links are important for an understanding of the topic of chemical equilibrium?  What extrinsic links show the place of equilibrium in the discipline of chemistry, and in the world of science?  How might we help students to realise these links and to appreciate their importance?


6.         Other components of PCK for any given topic include recognition of the scientists’ sources of knowledge (why we believe what we believe), an ability to distinguish between what is demonstrable knowledge and what is arbitrarily decided knowledge, and what the scientific community still does not know about the subject.


In addition, a teacher with good PCK will know what chemistry education research has to say about students’ understandings of the subject.  What do students find difficult, and what is not so difficult?  What is the source of the difficulties?  What misconceptions are common?  What recommendations are made for avoiding or “curing” them?  Such a teacher would also have an acute awareness of the tension that may exist between attempts to simplify the subject matter for immediate “learnability” and either veracity or long-term teaching goals.  Hawkes (1995; 1996) publishes regularly in the Journal of Chemical Education on this issue.

To achieve the sorts of understandings identified above, a teacher might have a vast store of PCK in the form of a repertoire of teaching strategies to call upon as appropriate – including analogies, laboratory experiments, classroom demonstrations, concept mapping tasks, Venn diagram tasks, assignments, or projects.  And this teacher will understand the specific purposes of each of these strategies, their strengths and weaknesses, and the appropriate moment to use each of them.  I believe that the “pedagogical-content knowledgable” teacher is better placed than otherwise to make sound choices between alternative courses of action, based on content-specific reasoning, in order to maximise richness of learning.  Of course one needs to recognise that classroom decisions cannot be made entirely on content-specific grounds.  Any teacher will, with some degree of consciousness, take into account his/her educational philosophy, system constraints, colleague support, colleague constraints, and understanding of the motivations and the abilities of the students.


Again I point to the incredibly diverse and demanding range of skills needed for good teaching.  Are these any less, in terms of difficulty of acquisition or responsibility of administration, than the skills of lawyers, sharebrokers, politicians or research chemists?  Where to?

In the teaching profession the accumulated PCK of each of its participants grows with experience, peaks at retirement, and then disappears – often with hardly a contribution to the collective wisdom of the profession.  What other profession would accept this state of affairs?  While in other professions, successive standard-bearers “stand on the shoulders of giants who came before them”, the teaching profession seems to be engaged in many-fold “re-inventions of the wheel”.  I recommend two courses of action:


1.         For each topic in chemistry, teachers, chemists and chemistry education researchers should work together, integrating pedagogy, chemistry and research findings, to systematically create and document a pool of PCK.  I do not envisage that this collection of PCK should be prescriptive.  The collection might, however, constitute a research-based resource pool of notes, ideas and strategies relevant to the teaching and learning of the subject matter, into which all chemistry teachers might dip.  There are, of course, already a myriad of teaching tips and discussions to be found about the teaching of particular topics dispersed throughout the science education literature.  But there is not a systematic collection of these, with evaluations and comparisons.  Furthermore, I believe that recent research findings and yet-to-be-done analyses of the particular demands of understanding particular topics, will lead to new PCK.


2.         Architects, chess players and lawyers can learn from documented case studies that exhibit the philosophies and skills of masters in their field, indicating their “game plans”, their strategies, tactics, and responses to particular problems and situations.  Wouldn’t chemistry teaching benefit from research which provided detailed case studies of master teachers teaching about chemical equilibrium, for example?  This “applied research” (in the sense that it is not necessarily directed at extending theory, but attempting to provide insights into real problems) would not only describe the master teacher’s actions, but also probe his/her thought processes at critical points during a course, and track the changing understandings and perceptions of the students.


There are previous reports of observations, akin to case studies, of teachers’ use of content knowedge in the classroom (Garnett, 1987; Munby & Russell, 1992; Wilson, Shulman, & Richert, 1987), but in these the subject matter has been merely the vehicle for making interpretations about the generic nature of teacher knowledge. The moment seems to be crying out for studies which, in the light of these generic characterisations, observe, interpret and evaluate the PCK used by particular teachers in instruction of a particular topic, to illuminate the teaching of that topic, rather than to illuminate teaching in some generic sense.  In a word, it would be useful to know “what works” in terms of specific content-related decisions, for master teachers.

There already have been exploratory attempts to describe pedagogical content knowledge pertaining to particular chemistry topics.  Examples include those by Geddis et al. (1993), Magnusson and Krajcik (1993), and De Jong et al. (1995) which refer, respectively, to the content-related demands of teaching about the topics of isotopes, thermodynamics and oxidation-reduction chemistry.  Hopefully these represent the beginning of an accumulation of such analyses, which would be extremely useful for both the pre-service education and the professional development of chemistry teachers.  And they might even be useful resources for chemistry students – especially those at the tertiary level.



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