- Emily Rose Seeber

# Modelling vs Representation in Chemistry

In 'Who is a Modeler?', Michael Weisberg argues that we often confuse the practice of modelling, with *abstract direct representation*, or ADR for short. Both are ways of representing some real world scientific phenomenon, and gathering information from the representation to answer questions about the real world.

This all seems very abstract, but I think Weisberg's distinction between the two practices is interesting for reflecting on curriculum design in Chemistry, to ensure that students have the opportunity to develop *both* kinds of practice.

**First things first**

I am *not *discussing the results of these two practices, models and ADRs, in this blog. So, I am *not* evaluating whether the Periodic Table is a model or not, or the Bohr model of the atom, or even the particle model.

I *am* interested in how students could be given the opportunity to do some modell*ing*, or some ADR-*ing*. I am interested in the practice, the activity, not the ontological status of the result.

I'm going to start with ADR, as this is by far the more common form of representation used in Chemistry lessons.

**So what's abstract direct representation?**

Weisberg's exemplar for this practice is the great Mendeleev. "Mendeleev examined elemental properties, worked out which properties were essential and which ones could be abstracted away, and then constructed a representational system that elucidated important patterns and structure among the elements." This differs from modelling because Mendeleev "represented chemical phenomena *directly*, without the mediation of a model". The periodic table is *real *representation of *real* properties of the elements.

**Learning Chemistry through ADR**

Giving students cards with information about various elements for the students to organise into a sensible representation, and derive the Periodic Table.

Asking students to do an investigation into the properties of metals and construct a way of organising them to deduce a kind of reactivity series using their own data.

Giving students some information about benzene, and then having them refine their structures as they receive more and more experimental data. (A set of task cards for this activity is available

__HERE__.)

**What does it mean 'to model' in Chemistry?**

In contrast, the modeller uses an indirect representation to study the world. The modeller creates something similar to real phenomena, and then studies that to make deductions about the real world. They can then go on and test their model.

Weisberg suggests that *if* Mendeleev were a modeller, then he would have simplified the elements, and set up hypothetical links between them, then analysed the model for its logical consequences, such as trends in reactivity. But this was not the practice of Mendeleev. So he was not a modeller.*

**Chemical modelling with students**

Tasking students with designing a model for the greenhouse effect. I've done this in Key Stage 3 lessons and been blown away by the creative thinking of students, from constructing 'greenhouses' from straws and clingfilm, to the simple, but powerful use of an absorbent solid to soak up water (the heat energy).

Asking students to develop a model to explain how rate of reaction changes with different experimental conditions. They may come up with something like collision theory, or they may not. And if they come up with something different, then you can work together to compare and evaluate the different models.

Asking students to develop models of the atom which account for some of the properties that scientists were aware of at the time of Bohr's model. Students can then choose which aspects of the data to incorporate into their model and which to ignore. And can choose how to represent their model. I have had great success suggesting that cake is an effective medium for modelling in the past. Not sure why...

In the language of Tom Sherrington (*The Learning Rainforest*), modelling is real 'canopy' stuff. ADR is a little more accessible, and easier to fit into schemes of work, but done well it can really stretch and engage students with generating scientific ideas.

Modelling and representation both push learning beyond the knowledge acquisition aspect, into the more creative and experimental. And they work best when students have strong knowledge bases to draw upon. For example, constructing an ADR for the reactivity of metals, requires students to have a strong knowledge of reactions of metals, investigative procedure, analysis of results, and much more. However, *when we have the right conditions in place*, ADR-ing and modelling really challenge students' thinking in different and thrilling ways.

And, as teachers and curriculum designers, we can use Weisberg's distinction to ensure that we include a range of philosophically and cognitively distinctive forms of representation into our teaching schemes so that students have the opportunity to engage in a rich spectrum of scientific practices. Not just using representations and evaluating models. But constructing them.** For themselves.

*We can still call the Periodic Table a 'model' if we want. Again, I am looking at the practice of modell*ing*.

**On different occasions.

#chemistry #practical #PCK #philosophyofscience #pedagogy #curriculumdesign