Modelling in science lessons: Are there better ways to learn with models?

School Science and Mathematics, Dec 1998 by Harrison, Allan G, Treagust, David F

Models and Modelling in Learning Chemistry Apart from its macroscopic properties, chemistry relies on models to describe and explain all its chemical and physical changes. Symbolic models -- chemical formulae and equations -- supply chemistry's special language, and mathematical, theoretical, and conceptprocess models explain fundamental concepts like atomic theory and reaction mechanics. How well could chemistry be taught without the periodic table model of element properties? At yet another level, interactive multimedia simulations have the potential to make topics like equilibrium more understandable at the particle level. Modern chemistry simply cannot be taught without models, and the ubiquitous presence of atomic and molecular models in chemistry lessons is evidence of theirnecessity. Diagrams like those in Figure 1 feature in many chemistry textbooks and illustrate the "taken-for-granted" role of models in chemistry.

Observations from 8th-llth-grade

To determine how 8th- through Oth-grade chemistry students reacted to scientific models of atoms and molecules, we surveyed 48 Australian science students attending three different schools (a prestigious girls college, a large city high school and a rural high school) and found many common model-based alternative conceptions (Harrison & Treagust, 1996). Language common to both biology and chemistry (e.g., nucleus and shells) is a major source of confusion for some students. Several students concluded that atoms can reproduce and grow and that atomic nuclei divide. Electron shells were visualized as shells that enclosed and protected atoms, while electron clouds were structures in which electrons were embedded. These synthetic models are likely generated during discussion as a result of semantic differences between teachers' and students' understanding of concept-metaphors. Students also expressed a strong preference for spacefilling molecular models, and only two students held a satisfactory model of the spaciousness of atoms. The alternative conceptions seemed to be related to the students' believing that there is a one-to-one correspondence between the models used and reality. Fifty-eight percent of the students were found to be Level 1 modellers.

This raised the question as to whether teaching chemistry using systematically presented models could improve a class of eleven 1 lth-grade students' understanding of model structure and purpose. A decision was made to present chemistry 's commonly used analogies and models of atoms and molecules using the systematic FAR teaching framework and to socially negotiate the shared and unshared attributes of each analogy and significant model. Whenever molecular models were used in class, especially in the organic chemistry unit, Allyn and Bacon modelling sets were available on each student's bench, and the students were encouraged to make every molecule discussed. The students were keen to build these molecules and spent most of their spare time playing with the model sets. Special pedagogical analogical models like the balloons model of the tetrahedral shape of sp3 molecules (e.g., methane, Figure 2) were demonstrated and discussed in class.