Media - Essentials of Chemical Education - page 103

Models . Concrete models of the structure of matter, model drawings, mental models,
model experiments, or functional models are important media for chemistry teaching.
These kinds of models and their discussion form the contents of Chap. 6.
Especially first models of the structure of matter according to the special
arrangement of smallest particles (particle model of matter, see Fig. 6.11) have to
be introduced. Later, the arrangement of atoms in molecules or ions in ionic
structures will be introduced (Dalton's atomic model, see Fig. 6.12). On the base
of D ALTON'S atomic model, it is very important to describe chemical reactions and
the rearrangement of atoms in molecules, for example, the reaction of H 2 molecules
and O 2 molecules to form H 2 O molecules (see Fig. 7.6), or the rearrangement of
ions to explain the precipitation from salt solutions (see Fig. 7.8).
Using molecular model sets or closest sphere packing means to take nice colored
spheres of wood, cellulose, or plastics, and to take glue or sticks to combine those
spheres. Because students like to take these colorful media as originals, they may
think that S atoms are yellow and C atoms are black. These misconceptions should be
avoided by discussing the “irrelevant items” of the concrete models (see Fig. 6.1):
the atoms or ions have no color because no one can see them; there are no sticks or
glue between the atoms or ions because they are attracted by electric forces, the
material of the models is irrelevant, etc. The models have to only show the spatial
arrangement of atoms or ions (the chemical structure), different spheres in sphere
packing may show the ratio of diameters of atoms or ions, they may also show the
ratio of the numbers of atoms or ions in their arrangement.
Models can also be shown on the computer screen: these representations are
even more accepted as models because there are no real spheres, sticks, or glue. We
have different programs to create molecular models or crystal structures, and these
programs exist in such big numbers that it is nearly impossible to offer detailed
information.
4.2 Scientific Ideas: Appropriateness of Media
Educational supply companies as well as educational publishing companies offer
a lot of transparencies, slides, videos, drawings, and pictures; often those are
different media for one and the same issue. Their scientific appropriateness should
be evaluated before use in class based on the following criteria.
Validity . Before the use of any medium in class, it should be checked if it is
correct from the view of the scientist or if it can be brought up to date in scientific
terms.
There are - for example - many visualizations or transparencies of the atomic
structure according to the nucleus-shell model, which uses isolated spheres as
models for electrons or circles for their movement around the nucleus. This requires
much additional information, which starts from the wave-particle duality and brings
terms like energy levels into the discussion. Since protons, neutrons, and electrons