Chemistry Reference
In-Depth Information
crystals, their dissolution in water and the sugar solution are discussed on the
substance level. Rapidly moving sugar particles and water particles can work as
mental models. Red balls and blue crosses can be used for a model drawing on the
concrete models level. Absurd combinations and wrong mental models like “sugar
solution consists of red balls and blue crosses” or “sugar particles are red balls and
taste sweet,” would result if terms from different levels are being mixed.
7.2.2 Chemical Symbols
“When we ask adults about what they still remember from their chemistry lessons at
school, we see a problem that our students today also have. Usually we get the
following answer: 'oh, there were formulas'. And people are proud when they still
know what H
2
SO
4
is - not what it means: more chemical knowledge did usually not
survive. A senior administrator on a board of education, who had studied science,
once said to me: 'Do not tell me about the educational value of chemistry -
chemistry means only formulas!'” [
10
]. Scheible [
10
] states elsewhere: “The
chemical formula has discredited us.” These comments show that it seems to be
difficult to raise sufficient understanding of chemical symbols or formulae during
chemistry lessons.
Chemistry lessons without formulae.
The problems of symbol language can be
avoided in beginning lessons by some simple methods: using descriptions from
everyday life, names for substances instead of formulas, verbal reaction equations
with the symbols (s), (l), (g) or (aq):
þ
!
;
hydrogen chloride (g)
water (l)
hydrogen chloride (aq)
exothermic
þ
!
þ
;
hydrochloric acid
magnesium (s)
magnesium chloride (aq)
hydrogen (g)
exothermic
The difference between the symbols (l) and (aq) has to be explained by pointing
out the difference between pure liquid hydrogen chloride (l) with a boiling temper-
ature of - 85
C and the aqueous solution of hydrogen chloride, which is commonly
called hydrochloric acid.
Symbols on the level of the particle model of matter.
In addition to verbal
reaction symbols one can introduce concrete models on the basis of the particle
model for a better understanding of chemical processes (see Fig.
7.5
). It is necessary
to add the names of the particles in the drawing: sugar particles, water particles
(“H
2
O particles” are a contradiction because the composition “H
2
O” only should be
explained on the level of Dalton's atomic model).
Close-packed arrangements of spheres can be built during chemistry lessons to
demonstrate the spatial arrangement of metal particles like silver particles or copper
particles in crystals (described in Chaps. 6 and 10). Also sugar particles can be
