Chemistry Reference
In-Depth Information
found the first table of atomic masses: The scientific way of chemistry started with
these ideas!
This fascinating story of the discontinuity hypothesis and the disprovement of
the “horror vacui” theory should be transferred to our students and to the planning
of chemistry lessons regarding the structure of matter and the involved particles.
1.2 Learner: Empirical References of Student Conceptions
According to Piaget students starting with chemistry lessons can mostly be assigned
to the period of concrete operations in their intellectual development - their
thinking is tied to concrete reality. Therefore, they explain phenomena in a concrete-
pictorial and in a magical-animistic way of speaking. This becomes apparent in the
following examples:
- Pieces of wood
don't want
to burn, the flame
wants
to go out
- The flame
eats
the candle, substances
like to
react, hydrogen
likes
to react with
oxygen
- Acids
attack
other substances, acids
eat
base metals, rust
eats up
iron, etc.
Student interpretations are often basic analogies; reasons are being personalized
and equalized to purposes:
- Sodium reacts with water “like a fizzy tablet”
- When copper sulfate dissolves it looks “like distributing red-cabbage juice in
water”
- Crops grow on fields
so that
humans can eat it
- Wood burns
so that
one can warm themselves, etc.
Parallels between the historical development of chemistry and students' way of
thinking can be found. For this reason, the concepts from science history stated in
Sect.
1.1
will be taken up and compared to empirically observed examples of
today's student comments.
Substances as a bearer of properties
. Chemical reactions do not necessarily
produce new substances, but new properties are being added according to student
conceptions [
7
]:
- Copper roofs turn green, silver turns black, a solution turns deep blue, etc.
As for philosophers of ancient times, a “primary matter or a bearer of properties”
seems to exist that survives and only changes the outward appearance again and
again. Therefore, it should be made clear to the students that:
- The green layer on a copper roof can be removed: it is copper carbonate
- The black layer on a silver spoon is not silver: it is silver sulfide
- A solution changes color because of a new dissolved substance
