FROM THE SPECTRUM TO THE ATOM: AN INQUIRY-BASED TEACHING-LEARNING SEQUENCE ON ATOMIC SPECTRA AND BOHR’S ATOMIC MODEL

Modern physics is present in our everyday life in many ways and it will become even more important in the future. Therefore, teaching and learning modern physics in secondary schools can no longer be avoided.

In the past 15 years, modern physics has been included in most secondary school standards, but still in a rather marginal way. The conceptual complexity of modern physics is often a hurdle for teachers as well as for students; as a consequence, most schools adopt narrative/historical approaches which, however, are not sufficient to grasp the deepest conceptual aspects of modern physics, nor to deal with its technological applications. Teaching modern physics in secondary school is therefore a challenge that calls for a close collaboration between physics teachers and physics education researchers.

This contribution presents the design, development and testing of a research-based teaching-learning sequence (TLS) on atomic spectra and their role in the construction of the atomic model, in particular the structure of energy levels postulated by Niels Bohr. The spectroscopic approach was chosen since it provides a simple experimental approach to the exploration of quantum phenomena; moreover, by focussing on the representation of energy levels rather than on electronic orbits, we avoid reinforcing the planetary model of the atom, a pre-quantum model that does not describe the “real” quantum physics.

The TLS was designed using an Inquiry-Based Learning (IBL) approach. IBL has been recognised as one of the most effective approaches in science education, since it allows not only to learn science in a meaningful way, but also to understand the way in which scientific knowledge is built. Specifically, our TLS featured:
(a) a pre-test and pre-lab session, where students’ initial ideas were elicited and valued;
(b) a laboratory session where students built their own spectroscope and used it to visualise and analyse the spectra of different light sources, including atomic spectra;
(c) a post-lab session where students analysed their data and interpreted them in order to construct an explanation;
(d) a systematisation of the students’ knowledge and
(e) a post-test. The TLS was designed within an action–research paradigm, in collaboration with a physics teacher, and was implemented in a fifth-year classroom (13th grade) of an Italian “Liceo Scientifico”.

We evaluated the TLS from multiple perspectives using three different instruments: a pre/post test to evaluate students’ gain in knowledge and skills, observation rubrics to evaluate students’ involvement and participation, and the analysis of students’ artefacts (lab and post-lab worksheets) to gain insights into the process of knowledge building. The pre/post test comparison suggests that almost all of the students had a positive evolution in their understanding of the atomic model, both qualitatively and quantitatively. The students who reported lower gains were the ones who participated less actively in the lab sessions and group work, according to the observation rubrics. Finally, the analysis of lab/post-lab worksheets revealed that the most productive moment for knowledge building was the cognitive conflict that arose when students tried to match their experimental data to the equations, which brought them to question their reasoning and to generate new explanations. Small group discussions were crucial to guide the students towards the correct interpretation and to foster understanding.