Media - Essentials of Chemical Education - page 104

can hardly be illustrated by spheres or dots, it should be avoided to use these
ambiguous media trying to explain the structure of atoms, ions, or molecules.
Didactical reduction . Many topics have to be didactically reduced to match the
class's learning conditions or students' cognitive development. In this context,
Reiners [ 9 ] talks about special knowledge transformation or “didactics as a trans-
formational science.”
In any case it needs to be tested, if such reductions are acceptable in terms of
content. Some decades ago, there were pictures of models in school topics that were
based upon the idea of “elements being made up of atoms and compounds being
made up of molecules.” (see Fig. 4.2 , upper part) The authors of such drawings [ 10 ]
knew that the element sulfur is made up of S 8 molecules and they also knew about
the ionic structure of iron sulfide: nevertheless, they thought that their drawings
concerning “FeS molecules” were didactically acceptable reductions. In addition,
the statement that one molecule shows the “smallest portion of a compound” is
totally incorrect from a scientific point of view and therefore these reductions are
not acceptable.
Today didactic reductions are allowed as long as the content stays correct. It is
acceptable to describe the reaction of copper oxide and hydrogen with models of
lattices and molecules (see Fig. 4.2 , lower part). The model shows the rearrange-
ment of atoms [ 11 ], in subsequent lessons copper oxide can be explained with ions;
and the size of atoms compared to those of the ions may be corrected.
Real objects, real processes . If the opportunity arises to use real objects instead
of pictures or transparencies in class, the real object should always be favored.
However, they should be accompanied by photos or model drawings, to produce

The chemical formula stands for the chemical compound and for the smallest
part of the substance, the molecule.

By combining atoms to form a molecule no bond remains unoccupied.

iron sulfide

iron sulfur

Fe S Fe S

one Fe atom one S atom 1 molecule iron sulfide

Fe

S FeS

Copper oxide

hydrogen copper water

Fig. 4.2 Didactical reductions in the 1950s [ 10 ] and today [ 11 ]