Chemistry Reference
In-Depth Information
because it is impossible to see them - neither with a magnifying glass nor with the
best microscope.
Because particles are not visible, one tried all times to develop suitable mental
models. Demokritus and other Greek philosophers came up with the idea of the
atom more than 2,000 years ago - simply by thinking about their observations
concerning matter and trying to find out the composition and structure of matter.
L
´
mery developed a particle model for the effects of acids [
1
]: “All acids are
composed of particles like biting points, all experiences show that acids make
pricks, which everyone can feel on the tongue.” L´mery had never seen acid
particles, but he tried to transfer macroscopic characteristics of acids on the cited
mental model.
Nevertheless structural and mental models are very important for the under-
standing of science, especially chemistry. One of the key questions of chemistry
education deals with the scientific idea of models and how these can be transferred
to young learners at school. To get the idea across, general characteristics of models
have to be looked at first and later transferred to scientific models.
General characteristics of models
. Following an empirical analysis of models in
general Stachowiak [
2
] differentiates three basic characteristics:
- Feature of depiction: models are always a model of something, namely illus-
trations and therefore representations of certain natural or artificial originals.
- Feature of shortening: models do not cover all characteristics of the original,
they represent only the ones that seem to be relevant in a particular context.
- Feature of subjectivity: models fulfil their functions of representation and sub-
stitution only for certain subjects, limited to certain mental or real operations,
limited to certain time.
Take the picture of the Neuschwanstein Castle another time. It copies the
building and the surrounding landscape with fields, trees, roads and mountains in
the background downscaled: the feature of depiction is fulfilled. Some of the many
shortenings of the original are the missing space dimension, the nonexistent
patterns of light and shadow on walls and windows of the castle or the missing
motion of trees and branches in the wind: feature of shortening. The specific view of
the castle on the picture or the details of the landscape are subjectively chosen by
the photographer for a special purpose: feature of subjectivity.
Taking two different maps of the London Underground show that feature 1 is
fulfilled: they all show where the underground stations are located. Comparing
them one shows the streets close to the stations, the other one not: the shortening is
done differently. The differences are due to the users: some need the street maps
around the stations, other ones not because they are traveling every day the same
stations to work and back at home: feature of subjectivity.
