The atomic hypothesis is the primary concept of the scientific knowledge. When we teach atoms we give the key to unlock many of the doors across the sciences in physics and biology. There is an interesting lack of agreement when students should be introduced to the concepts of an atom and molecule. There is a view (AAAS, 2001; Taber, 2002) that says the ideas should be left until near the end of the secondary school, because only a few students can comprehend the idea of atomic and molecular particles. Research in science education during the last twenty years has shown students’ difficulties and misconceptions about the atom concept (Taber, 2002; Harrison and Treagust, 1996; Lee et al. 1993; Cokelez and Dumon, 2005).

In Hungary we introduce the concepts of atoms and molecules in the 7^th grade (age 13). Chemistry teachers use the atom concept as a useful ‘mental tool’, which helps the students conceptualise the molecular level systems. The particle theory is based on the atom concept. For the 7^th graders we teach different definitions of an atom: (1) an atom could not be divided up (Democritus); (2) the atom could not be divided by chemical methods (Dalton); (3) constituents of an atom (4) model of an atom (Rutherford, Bohr).

This study investigates how students describe atoms when they are presented with an open-ended question, and what hierarchy their responses can be arranged in.

730 students (grade 7-11, age 12-17) from 17 Hungarian secondary schools were questioned. Students’ responses were analysed by phenomenography (Marton, 1986) similarly to those that were done in the case of 239 high school students (grade 9-12) in the USA (Unal and Zollman, 1999). Data about the American students were obtained from the paper of Unal and Zollman (1999).

Categories extracted from the students’ responses were (a) units of matter; (b) constituents of an atom; (c) model of an atom. Unal and Zollman suggest the hierarchical structure of the categories and their combinations as follows: ‘units’ ® ‘constituents’ ® ‘units’ and ‘constituents’ ® ‘model’ ® ‘units’ and ‘model’ ® ‘constituents’ and ‘model’ ® ‘units’, ‘constituents’ and ‘model’. However, we were interested in the connection between these categories. For this purpose we tried to use a method similar to the knowledge space theory (Doignon and Falmagne, 1999). We searched for a model of the cognitive organisation of these categories, which would best fit the students’ response structure.

Our results show that generally the ‘model of an atom’ is built on the ‘constituents of an atom’, and the category ‘units of matter’ is separated from the other two categories. This is a very logical hierarchy of the categories, because the constituents of an atom (protons, neutrons and electrons) are the starting point of the models of an atom. However the ‘units of matter’ (the smallest particle of the matter) category is incompatible with the constituents and models of the atom.

On the other hand, we found inverse connection between categories ‘constituents of an atom’ and ‘model of an atom’ in grade 9 in Hungary (and in grade 10 in the USA). The probable explanation for this exception is that students learn a lot about the models of an atom in grade 9 in Hungary, and they deduce the constituents of the atom from the model of the atom. In the case of Hungarian 11^th graders we have not found any connection among the three categories mentioned above. This result shows that students’ knowledge structure regarding the concept of the atom disintegrates after finishing chemical studies at school.

Our research shows that combining phenomenography and knowledge space theory makes it possible to explore the fine structure of the organisation of categories in students’ minds.

 References

 AAAS Project 2061 (2001): The American Association for the Advancement of Science's, http://www.project2061.org

Cokelez, A. and Dumon, A. (2005): Atom and molecule: upper secondary school French students’ representations in long-term memory. Chemistry Education: Research and Practice, 6, 119-135.

Doignon, J-P. and Falmagne, J-C. (1999): Knowledge Spaces. Springer-Verlag, London

Harrison, A.G. and Treagust, D.F. (1996): Secondary students mental models of atoms and molecules: implications for teaching science. Science Education, 80, 509-534.

Lee, O., Eichinger, D.C., Anderson, C.W., Berkheimer, G.D. and Blakeslee, T.D. (1993): Changing middle school students' conceptions of matter and molecules. Journal of Research in Science Teaching, 30, 249-270.

Marton, F. (1986): Phenomenography – a research approach to investigating different understanding of reality. Journal of Thought, 21, 29-39.

Taber, K. (2002): Chemical Misconceptions: Prevention, Diagnosis and Cure. Vol 1: Theoretical Background. Royal Society of Chemistry, London

Unal, R. and Zollman, D. (1999): Students’ description of an atom: a phenomenographic analysis. http://perg.phys.ksu.edu/papers/vqm/AtomModels.pdf

This work was supported by OTKA (T-049379).