Arguments, Contradictions, Resistances, and Conceptual Change in Students’ Understanding of Atomic Structure MANSOOR NIAZ, DAMARYS AGUILERA, ARELYS MAZA, GUSTAVO LIENDO Department of Chemistry, Universidad de Oriente, Estado Sucre, Venezuela 6101A Received 8 December 2000; revised 6 September 2001; accepted 9 January 2002 ABSTRACT: Most general chemistry courses and textbooks emphasize experimental de- tails and lack a history and philosophy of science perspective. The objective of this study is to facilitate freshman general chemistry students’ understanding of atomic structure based on the work of Thomson, Rutherford, and Bohr. It is hypothesized that classroom discus- sions based on arguments/counterarguments of the “heuristic principles,” on which these scientists based their atomic models, can facilitate students’ conceptual understanding. This study is based on 160 freshman students enrolled in six sections of General Chem- istry I (three sections formed part of the experimental group). All three models (Thomson, Rutherford, and Bohr) were presented to the experimental and control group students in the traditional manner, as found in most textbooks. After this, the three sections of the experi- mental group participated in the discussion of six items with alternative responses. Students were first asked to select a response and then participate in classroom discussions leading to arguments in favor or against the selected response and finally select a new response. Three weeks after having discussed the six items, both the experimental and control groups presented a monthly exam (based on the three models) and after another 3 weeks a semester exam. Results obtained show that given the opportunity to argue and discuss, students’ understanding can go beyond the simple regurgitation of experimental details. Performance of the experimental group showed contradictions, resistances, and progressive conceptual change with considerable and consistent improvement in the last item. It is concluded that if we want our students to understand scientific progress and practice, then it is important that we include the experimental details not as a “rhetoric of conclusions” (Schwab, 1962, The teaching of science as enquiry, Cambridge, MA, Harward University Press; Schwab, 1974, Conflicting conceptions of curriculum, Berkeley, CA, McCutchan) but as “heuris- tic principles” (Lakatos, 1970, Criticism and the growth of knowledge, Cambridge, UK, Cambridge University Press, pp. 91 – 195), which were based on arguments, controversies, and interpretations of the scientists. C  2002 Wiley Periodicals, Inc. Sci Ed 86:505 – 525, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/sce.10035 Correspondence to: Mansoor Niaz; e-mail: mniaz@sucre.udo.edu.ve Contract grant sponsor: Consejo de Investigaci´ on, Universidad de Oriente, Venezuela. Contract grant number: CI-5-1004-1002/2001. C  2002 Wiley Periodicals, Inc.