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.
‘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.
