Atom and molecule: upper secondary school French students ...

A. Cokelez and A. Dumon 130
Figure 7: Comparative study of the levels of description of water molecule
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Answers
(%/R)
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L.0 L.1 L.2 L.3 L.4 L.5
Grade 10 43 54 2 1 0 1
Grade 11 26 52 7 11 3 1
Grade 12 44 37 7 9 3 1
In some descriptions of the water molecule, the following can be observed:
• The notion of the polarity of the molecule (11% of grade 11 students), The idea is
introduced at the beginning of grade 11, at the same time as the students answer the
questions. In grade 12, only 2% of the students refer to it.
• An explicit mention of the angle between the O-H bonds (5%, grade 11 students; 10%,
grade 12). The accurate value is not often given.
Students’ misconceptions
As noted by Pereira and Pestana (1991), when dealing with the diagrams of molecules
with the help of space-filling models and ball and stick models, students do not always show
the respective size of atoms: 33%, grade 10; 7%, grade 11; 15%, grade 12. The radiuses of
the circles that represent oxygen and hydrogen atoms are generally equal.
Some students confuse atom and molecule in the description: “the water molecule
consists of two molecules of hydrogen and one of oxygen” (12%, grade 10; 3%, grade 11 and
8%, grade 12). In grade 10, they also sometimes refer to dihydrogen or dioxygen to name
atoms (7%), thus showing confusion in their conceptions.
Attributing colour to atoms in the description of water molecule (for example: “one red
circle and two white circles”) remains from grade 10 to grade 12 (6%, 3%, 5%) and 8% of
grade 12 students still think that the molecule possesses macroscopic properties. These
students thus seem to have difficulty in distinguishing model from reality. Indeed, the colour
code for atoms was developed when the representation of molecules relied on the use of
molecular models.
The poor understanding of what the chemical formula, H 2 O, represents (Ben-Zvi et al.
1988; Keig and Rubba, 1993) leads some students to produce an erroneous description or
drawing diagram of the water molecule: H and 2O (or H 2 and O): 5%, 4%, 7%.
Lastly, 5% of grade 11 and 4% of grade 12 students believe that the bond between atoms
is of the ionic type (molecule consisting of ions or bonding resulting from an exchange of
electrons between atoms).
Chemistry Education Research and Practice, 2005, 6 (3), 119-135
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