Chemistry Reference
In-Depth Information
to be chosen as models of smallest particles. Especially the discussion of form,
color or material of the model as “irrelevant components” opens the chance to
introduce the idea of the scientific model even on this level. In the beginning the
particle model is used as a preliminary mental model. As lessons go along it
advances via Dalton's atomic model to the nucleus-shell model. At the end of
this topic, “the randomly drawn limiting line” may be discussed with students and
the demonstration of balls and circles should be critically evaluated.
Understanding of chemistry through models:
Figure
6.1
shows the scheme
“thinking in models” and thereby the process of perception in chemistry “from
left to right”: with the help of additional information a chemist works out a mental
model and transfers it to concrete models for visualization. Learners cannot go this
way, but they can make their way through the diagram “from right to left,” by
working first with concrete models: they observe and compare concrete models and
develop advanced mental models for relevant issues. It is often the case that mental
models interfere with irrelevant issues of display models, but an adequate abstrac-
tion happens more and more with time.
After the introduction of first mental models, for example the particle model of
matter or the Dalton model of atoms or molecules, chemical facts are to be interpreted
with those models, as long as it is possible on this level. Chemistry lessons should now
proceed double-tracked, and they should be structure-oriented (see Chap. 10):
Track 1: phenomena and laboratory experience.
Track 2: structural models and mental models (see Table
6.1
).
After the decision to introduce the
particle model of matter
, appropriate
phenomena and experiments are to be chosen. It is possible to take snow flakes or
crystals of sugar and to ask the reason why they have the same shape. The answer
should be the symmetrical arrangement of particles: water particles are arranged
in snow flakes in a special way, sugar particles in sugar crystals in a different way
(see Table
6.1
). It makes also sense to choose dissolution processes, for example the
dissolution of sugar in water (see Fig.
6.11
): the sugar particles are shown by dark
spheres, the water particles by light spheres, the dissolving process should be
interpreted by moving spheres: in the solution moving sugar and water particles
Table 6.1 The two-tracked approach in chemistry lessons
Track 1:
Phenomena
and
laboratory
experience
Same shape of crystals,
dissolving
processes,
diffusion,
distillation
Chemical reactions of
gases, gas laws,
Avogadro's law
Redox reactions of
metals and salt
solutions
Track 2:
Mental and
concrete
models
Particle model:
arrangement of
particles before
and after diffusion
or dissolution
Dalton's model: models for
arrangements of atoms and
molecules before and after
chemical reactions
Atomic structure:
electron
transfer from metal
atoms to ions in
solution, from ions
to atoms
