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

A. Cokelez and A. Dumon 122
As far as molecules are concerned, the model of a covalent bond has been already
introduced, and ball and stick models appear. Each stick between atoms can then be
associated with a shared electron pair.
The interpretation of the geometry of some simple molecules is based on taking into
account the repulsion of shared and unshared electron pairs around the central atom.
Grades 11 and 12
In grade 11, the representation of molecules with the use of molecular models is
generalized in organic chemistry. What is new is the introduction of the polar character of
some bonds, and of polar molecules.
Lastly, it is only towards the end of the Physics curriculum in grade 12 that the Bohr
model is introduced. It will thus not appear in our study.
Analysis of students' evolving representations of atoms and molecules
Review of the literature
While very few studies have been carried out in this field in France, a lot of research has
been conducted in Anglophone countries (UK, Australia, NZ, and Canada). Here, we present
the main findings relevant to our work.
Conceptions of the atom
An atom is often described as round, solid, hard (Griffiths and Preston, 1992; Harrison
and Treagust, 1996) and defined as a ‘ball’ or ‘sphere’ (Harrison and Treagust, 1996).
Therefore, the water molecule consists of two or more solid spheres (Griffiths and Preston,
1992).
Charlet-Brehelin (1998) shows that only slightly over a third of students who have
followed a traditional course of studies and have left Lower Secondary School (beginning in
grade 10) have internalised the minimum formulation level required at the end of grade 9: an
atom is made of a nucleus and electrons (electron suite). An identical observation is brought
out by Harrison and Treagust, (1996). Students generally produce four categories of models:
the atom as a sphere, solar system atom, neutral atom (positive charges of the nucleus equal
to negative charges of the electrons), and the atom as a nucleus surrounded by an electron
cloud. By the end of a traditional course of studies, the first two models are used by many
students, 41% and 48% respectively (Charlet-Brehelin, 1998). According to Harrison and
Treagust, (1996), many students represent an atom as a ‘simple circle’ within a large circle.
Even after teaching, there remains among students a certain degree of confusion between the
terms used: not only particle, atom, molecule, but also nucleus, proton, neutron and electron
and their interrelationships (Osborne and Freyberg, 1985; Johnston, 1988). For some
students, the number of electrons, protons and neutrons is the same for a given atom (Tsai,
1998). Keig and Rubba (1993) reveal that for many students (45%), electrons are preassembled
in electron pairs within the atom. According to Taber (1998) and Robinson (1998),
students use the rule of octet as a basic heuristic principle, to explain chemical bonding,
chemical reaction and ion formation. An atom is said to be stable if its valence shell is filled,
and is said to be unstable otherwise. The quantum model of the atom gives birth to the
representation of the electron cloud. But the fact that the students are willing to use this
representation at the end of grade 9 (Charlet-Brehelin, 1998) is no guarantee that they
understand its meaning. Harrison and Treagust (1996 and 2000) show that, for students, the
electron cloud is considered as a matrix in which electrons are embedded (as water drops in a
cloud) and Tsaparlis and Papaphotis (2002) report that upper secondary Greek students’
(grade 12) have greater difficulties in understanding the concept of ‘atomic orbital’.
Chemistry Education Research and Practice, 2005, 6 (3), 119-135
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