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TGB1: Notes on ‘the particle theory’
The particle theory

This page states the key ideas, while the following pages explain each of the ideas in more detail. It is important to
introduce the particle theory as a model: that is, a collection of ideas which do not necessarily describe exactly
how things are but which can help to predict how something is going to behave.
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‘A sample of a substance is a collection of particles’
At this stage, we are using a model to explain the processes of melting and freezing, and keeping the model as
simple as possible.

‘There is nothing else except the particles’
This is a difficult point for many students, who imagine the particles as being somehow ‘embedded’ in a matrix of
the substance. For this reason, try to avoid phrases such as ‘the particles in a liquid….’ You can read more about
students’ ideas in 'Key Features of Students' Understanding' in the Teachers’ Guide.

Notes about the animations
You may need to run the two animations a couple of times for students to see everything that is going on: it
shows a succession of magnifications of the surface, so one small square is enlarged to show 100 smaller squares,
then one of them is enlarged….. and so on until we get down to ‘particle size’ . It is not meant to show what the
surface looks like at each stage, just to help students track the process. The numbers show the magnification.
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main content b1.2

more info
tgb1: notes
tgb2: notes
tgb3: freezing
tgb4: notes
tgb5: notes
tgb6: freezing
tgb7: notes
more info
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