Theoretical models, submicroscopic

The existence of such ratios can be explained by the models chemists use of the structure of matter at the submicroscopic level, and indeed is part of the reason chemists initially adopted such ideas in an instrumental way that is, as ideas that worked as useful tools for thinking about chemistry, but which might not reflect an underlying reality. Over many years these ideas were found to provide a core set of models that could provide rmifying frameworks for making sense of chemistry Today most chemists consider molecules, atoms, protons, electrons and so forth to be real objects but it is important to remember that these ideas are a set of theoretical models, even if a very useftil and successful one. I am not suggesting these entities do not exist, but that our scientific models of these entities are subde and still being developed, and the mental models that most of us have of them are at best partial and approximate versions of the best descriptions science can currently offer. 

This is incredibly useful because it enables us as teachers to make shifts between the observations students can make in the laboratory and the explanations chemists develop in terms of theoretical models at the submicroscopic level. However, we may get so used to talking in this way that we can easily forget that students may not always readily follow these shifts in thinking, and what we say may seem like some magician s sleight of hand. So we might be talking... 

A central feature of the way chemistry is presented and discussed in classrooms is the set of representations (such as formulae and chemical equations) used. This is often seen as a third level distinct from the molar and submicroscopic levels, but is more helpfully understood as a specialised language that allows us to shift between those two levels (see Chapter 3). Translating between observable phenomena, symbolic representations and theoretical models is a key part both of teaching, and learning, chemistry. 

The first activity related to two models of the nature of matter at the submicro-scopic level. A core issue in teaching chemistry is that phenomena that can be directly observed (dissolving, burning) are commonly conceptualised at two very distinct levels (Johnstone, 1982) by a formal description and categorisation at the macroscopic level and through explanation of observed behaviour based upon theoretical models of the structure of matter at a submicroscopic scale (Taber, 2013). 

One of the most important features of modern chemistry is that it is a science that provides explanations of the reactions seen in the world at observable scales (at the molar or macroscopic level) in terms of theoretical submicroscopic entities such as molecules and ions and electrons. As chemistry teachers we are constantly shifting back and forth between the macroscopic descriptions and submicroscopic models this shifting takes place in our thinking and is reflected in our classroom talk. To follow our arguments and explanations, our students need to be able to follow these shifts. 

Chemical bonding is a theoretical idea that is a key part of the way matter is modelled by chemists at submicroscopic scales (as composed of extremely tiny quanticles , as described in Chapter 1) and so is not likely to be familiar to students from their experiences outside the classroom. However, if particle models are introduced in the manner recommended in this book (Chapter 2), students will have been introduced to the idea that the particles of which substances are made have holding power of varying strengths, which tends to cause them to clump together unless they have sufficient movement to overcome this. 

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