Chemistry Reference
In-Depth Information
with molecular models. Since the bonding of nonmetal atoms is usually represented
by push buttons on balls in molecular kits, it is fairly easy for the learner to build
molecular models independently. Thereby they become acquainted with atomic
bonding over time (see Fig.
6.5
and [
19
]).
If the learner observes the directed sticks from ball to ball in the molecule model,
these sticks can be interpreted as
directed bonding
between atoms. Subsequently it
is possible to understand the bonding of metal atoms in metals or of ions in salts
as
undirected bonding
and to separate this from the different bonding in mole-
cules [
16
]. It is also possible to differentiate the
finite
arrangement of atoms in
molecules from the
infinite
one of atoms or ions in crystals.
If at least two molecule kits are available and two different models are being
built for the same molecule, the fixation of one single model with all irrelevant
components can be prevented. In a discussion of these models the learner has to
find out similarities in both models and recognize them as the feature of depiction.
The same applies to sphere packings later on: if two models of different colors
and materials are being built for the same metal or salt structure, a one-sided inter-
nalization of material or color can be avoided.
In conclusion it should be pointed out that the spatial ability of the learner can be
enhanced with these three-dimensional structural models (see Chap. 10). Empirical
research has shown [
20
-
22
] that spatial ability increases with the construction and
discussion of structural models, with building up sphere packings to show metal
structures, with the comparison of octahedral or tetrahedral holes and coordination
numbers in ionic structures, with the intensive use of three-dimensional models of
the structure of matter in chemical education.
Adaptation and extension of models in chemistry lessons:
In most cases chemis-
try lessons start with the simple particle model of matter: one smallest particle is
chosen for every pure substance, for the substance copper the copper particle, for
water the water particle, for sugar the sugar particle. The assignment of carbon
particles causes difficulties since there are two substances: diamond and graphite.
But there are no specific graphite particles and different diamond particles. Carbon
particles exist in both substances: they build the diamond structure in a specific way
and the graphite structure in another way (see Fig.
6.15
). Carbon particles are
therefore neither colorless nor black - colors are characteristics of substances and
not characteristics of particles. The same applies to densities or melting temperatures:
they are not particle characteristics, but substance characteristics!
Applications and limits of models
. Table
6.2
shows that a specific model is not
fixed for every time: there are spiral curricular changes depending on purpose and
level of knowledge. Thereby one can indicate to the learner in chemistry lessons
that models and mental models have to be extended according to latest understand-
ing and knowledge - as it was the case historically.
In history the Greek philosophers were already discussing the atoms as “smallest
particles of matter.” In 1808 Dalton got the big idea that there are as many kinds of
atoms as elements, after discovering more and more elements. He brought us the
first table of atomic masses and the sphere as the first mental model of one atom.
In 1884 Arrhenius postulated ions as smallest particles of salts, acidic and basic
