Chemistry Reference
In-Depth Information
whether the learner's age group and stage of development is taken into account or
whether the media could create or confirm certain misconceptions.
Levels of abstraction
. Beginning with real objects and processes (see Chap. 4.2),
it should not be a single step to the highest level of abstraction - instead it is better
to choose appropriate media on an intermediate level of abstraction first. During the
introduction of chemical symbols, for example, which requires a high abstraction
on the submicroscopic level, an iconic illustration can help the learner to understand
the symbols (see Fig.
4.4
).
Starting from the real object, a cubical salt crystal, it is possible to discuss the
packing of spheres and the unit cell as media with an intermediate level of
abstraction. After that, symbols like Na
32
Cl
32
,Na
4
Cl
4
,Na
1
Cl
1
, or NaCl or the
ionic symbols like (Na
+
)
4
(Cl
)
4
, (Na
+
)
1
(Cl
)
1
,orNa
+
Cl
should be derived from
these concrete models. Chapters 6 and 7 delve into this problem.
In this way, learners gain an idea of the structure of substances and always have
it in mind, when they work with chemical symbols and formulae. When working
with iconic illustrations like structural models or model drawings, it is important
that the learner understands that these are models, and do not represent an exact
copy of reality. This problem can be minimized by working with different concrete
models for the same structure, like packing of spheres, crystal lattices, and unit cells
(see Fig.
4.4
). It is also possible to use red-green drawings of structures that create a
three-dimensional impression when seen through 3D glasses. Harsch and Schmidt
[
15
] offer further information about this innovative method.
Spatial ability
. Interpreting and understanding those structural models
(see Fig.
4.4
) is not easy for young students: to imagine the positions of spheres,
to count the coordination number 6, or to add the parts of spheres in models of the
Part of the structure
{(Na
+
)
32
(Cl
-
)
32
}
{(Na)
32
(Cl)
32
}
NaCl
Unit cell
Cl
-
ions:
6 x 1/2 =3
8 x 1/8 =1
Cl
-
Na
+
Na
+
ions:
Cl
-
12 x 1/4 =3
1 x 1/1 =1
{(Na
+
)
4
(Cl
-
)
4
}
Na
4
Cl
4
; NaCl
Fig. 4.4
Different models as media for deriving different symbols of sodium chloride
