Revisiting the chemistry triplet…

Revisiting the chemistry triplet

Taber, K. S. (2013). : drawing upon the nature of chemical knowledge and the psychology of learning to inform chemistry education. Chemistry Education Research and Practice, 14(2), 156-168. doi:10.1039/C3RP00012E

This is a perspective article published in Chemistry Education Research and Practice, which is a free access journal – anyone can download the article.

The title refers to the idea in chemistry education that teaching (and learning) involves the macroscopic level (what is seen and handled at the bench), the sub-microscopic level (theoretical models of atoms and molecules, etc.), and the system of subject-specific symbols used by chemists to represent chemical ideas (such as chemical formulae).

This was first pointed out decades ago by the late Alex Johnstone, and it has been widely recognised that teaching across these ‘three levels’ makes the subject challenging for students. This has come to be seen as one of the central ideas in chemistry education, as it is considered that it offers teachers a way to think about the complexity of what they are presenting to students, and asking them to make sense of.  “Revisiting the chemistry triplet…” offered an updated perspective on this theme.


The abstract reads:

Much scholarship in chemical education draws upon the model of there being three ‘levels’ at which the teaching and learning of chemistry operates, a notion which is often represented graphically in terms of a triangle with the apices labelled as macroscopic, submicroscopic and symbolic. This model was proposed by Johnstone who argued that chemistry education needs to take into account ideas deriving from psychological research on cognition about how information is processed in learning. Johnstone’s model, or the ‘chemistry triplet’, has been widely taken-up in chemistry education, but has also been developed and reconceptualised in diverse ways such that there is no canonical form generally adopted in the community. Three decades on from the introduction of Johnstone’s model of the three levels, the present perspective article revisits both the analysis of chemical knowledge itself, and key ideas from the learning sciences that can offer insights into how to best teach the macroscopic, submicroscopic and symbolic aspects of chemical knowledge.


Key points

The presentation in this article draws upon the idea that it may be helpful not to consider the three ‘levels’ as entirely discrete, as the symbolic level actually has a useful ambiguity (as formulae and chemical equations can refer to both substances, and to molecules) and so often acts as a bridge between the macroscopic and submicroscopic levels. It is useful to be able to talk about, say hydrogen chloride the substance, then write HCl to represent that, but to also see that as also representing a molecule as well as a sample of material. However,  if teachers use this affordance to shift between these two levels without being explicit about what they are doing, they can confuse learners.

The article also emphases a point sometimes missed when thinking of the triplet, which is the shift made between the actual phenomena observed and the theoretical language used to conceptualise and describe those phenomena. So students see crystals ‘disappear’ in a liquid, or something change colour, or give off smoke, and this gets redescribed as combustion or a redox reaction or a substitution or whatever. So there are two macroscopic levels of description: one in terms of phenomena as observed, and the other in terms of the formal chemical description – which can often be represented in symbolic language in a way that also represents an account of how the process is understood at the level of molecular interactions. Teachers of course, as experts, have often learnt to see phenomena in theoretical terms – they have learnt to short-cut the need to work to reinterpret what is seen, heard, and smelts in terms of formal concepts.

In part, the paper was meant to suggest to other chemistry education scholars that it might be time to refine the way we discuss and use the triplet in thinking and writing about the challenges of chemistry teaching and learning. However, I also hope the paper is sensible to classroom teachers of chemistry (whether chemists or other science teachers), and that it is useful in helping them reflect on how our teaching can overwhelm some students; and – more positively – how we can make the triplet explicit to help model to students something of the way chemists think about the world.



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