While constructivism has been widely discussed in science education literature (e.g. Fensham et al., 1994; Black and Lucas, 1994) and has been the theoretical basis of research into the learning of a wide range of biology and physics topics undertaken in many parts of the world (e.g. Duit, 1991; Pfundt and Duit, 1994; Carmichael et al., 1994) its use in chemistry has, on the whole, received scant attention. Although the importance of constructivism to chemistry has been recognised by some (for example, Laverty and McGarvey,1991; Watts, 1992; Garnett et al., 1995), much of the research undertaken from this perspective has related to elementary aspects of the subject (such as the terms element, mixture, compound and evidence for chemical change: Briggs and Holding, 1986). In this article we will discuss some results from a case study of the developing understanding of a student following an advanced level (A-level) chemistry course.
A core tenet of constructivism (Tobin and Tippins, 1993) is that learners actively construct knowledge to make sense of the world, interpreting new information in terms of existing cognitive structures. The bulk of research in the field has focused on `conceptual change learning', which, following Strike and Posner (1985) and Hewson and Hewson (1992), prompts learners to articulate their understandings in science in order to enable shifts in their conceptualisations of phenomena towards standard scientific explanations. A typical portrayal of conceptual change learning is of a fairly linear process of alteration from one conceptual framework of ideas to the next, en route towards scientific orthodoxy. For example, Driver et al. refer to the notion of a conceptual trajectory, 'a sequence of conceptualizations which portray significant steps in the way knowledge within the domain is represented' (1994a, p. 85). Progress can be through a gradual evolution of frameworks and through more sudden 'revolutions' in thinking as frameworks are challenged and radically changed.
Research such as Driver et al.'s (1994b) illustrates the possible multiplicity of conceptual frameworks used to describe and explain scientific phenomena, and it is quite usual to expect evidence of several different explanatory systems within any one classroom at any one time. Seldom, however, has research explored the range of explanatory frameworks used by individual learners as they work through a sequence of curriculum ideas. This is the approach we adopt here. It is an approach to modelling cognitive structure where the particular conceptions of a learner are not restricted to one framework, or to a sequence -- rather they are seen to be multi-faceted, connected but discrete, distinct and parallel conceptual frameworks.
CONCEPTS IN CHEMISTRY
There are several possible reasons why chemistry might have seemed an unpromising arena for constructivist research. For example, it is often highly abstract material which relies upon an understanding of other abstract conceptual systems, such as theories of the particle nature of matter. Research has shown that learners often have distinct misconceptions in this area (Brook et al., 1984) and demonstrate considerable confusion regarding the allied nature of intermolecular forces and their role in covalent bonding (Petersen and Treagust, 1989).
As students learn more about chemistry their cognitive structure is expected to develop in at least three ways: the range of their concepts will increase, the level of sophistication of their concepts will deepen, and their concepts will become better integrated with each other. It follows that developments in student understanding might be analysed by:
1. Looking for the appearance of 'new' concepts not previously used by the learner.
2. Observing how concepts are defined, explained and developed over time.
3. Noting how different concepts are related to each other by the learner.
An important issue for chemistry, however, is that concepts are often understood at varying levels of sophistication - and simplistic versions or models do not always cease to be useful just because more advanced conceptions become available (Taber, 1995a). …