Web site logical path: [www.psy.gla.ac.uk] [~steve] [best] [this page]

The three types of knowledge in chemistry

Alex Johnstone (see references below) pointed out that in Chemistry, students must learn in three different representations at once, and how to inter-relate each new concept or fact in all three domains:

1. Macroscopic: descriptive and functional (e.g. how chemical phenomena appear to the senses, colour, smell, density, etc.).
2. Formal or representational (the equations used to represent reactions).
3. Molecular, "submicro", explanatory: the invisible but 3-dimensional world of molecules' shapes and their dynamic motions, interactions, and kinetics.

There are several points about this.

• The third of the above is generally the hardest for students, and least well dealt with in teaching. It requires special attention educationally. (See also Roy Tasker.) It is a distinctive feature, and problem, of chemistry.

• However it is not necessary to teach all three domains to everyone, even though the combination and their inter-relationships are the essence of chemistry to experts. There are several reasons for this.
  • The obvious, and probably necessary, starting point for learners is connections to aspects of the world they already know [1]. You shouldn't teach the others without the macro; but you might teach the macro without the others.
  • The earliest, and so in important ways the most original, chemists, of course started here. So the macro may not be the latest knowledge, but it must be real science nevertheless. Thus it is foundational: not in the logico-deductive sense of a set of axioms from which other things can (now with hindsight) be derived, but in both the historical and more importantly the educational sense that the formal and microscopic are value-less (to humans) without the macro, but the reverse is not true.
  • You can teach and practise the scientific method solely in that domain: isolating variables, doing experiments.
  • If you then want to teach some systematic theory, then [2] is the next step. This does NOT necessarily have to be grounded in the micro. Thermodynamics, famously, can be and has been grounded axiomatically without any reference to the micro.
  • What is good for, and what delights, experts, is NOT necessarily what is good for, and delights, beginners. (It is natural to be "learner-centered" in the simplistic sense of treating learners as you would wish to be treated now, but in fact this is not always best for them. More attention to and respect for what a learner knows, and the way that puts them in a different intellectual place than you are in now, leads to a different response.)

• Every subject (as far as I can see) requires relating two domains, comparable to [1] and [2] above: macro and formal. This appears, for instance, in the Laurillard model as the relationship between the public/abstract and personal/perceptual aspects of a subject. Johnstone's insight into the nature of learning chemistry is a constraint on how general that is. It seems some subjects require more than two aspects to be addressed and inter-related, at least at the HE level of the subject.

References

A.H. Johnstone (1991) "Why is Science Difficult to Learn? Things are Seldom What They Seem" Journal of Computer Assisted Learning vol.7, 75-83.

A.H. Johnstone (1993) "The development of chemistry teaching" Journal of Chemical Education vol.70 no.9 pp.701-705

Web site logical path: [www.psy.gla.ac.uk] [~steve] [best] [this page]
[Top of this page]