UC Berkeley

This dissertation aims to explore how students think about atomic absorption and emission of light in the area of introductory quantum chemistry. In particular, the impact of classical ideas of electron position and energy on student understanding of spectra is studied. The analysis was undertaken to discover how student learning can be characterized along different dimensions of competence, and to determine the strength of the correlations between these dimensions.

The research in this dissertation study comes from a set of semi-structured clinical interviews after a unit on quantum chemistry using a stratified random sample. Open-ended questions were asked on the topic of atomic spectra to a representative sample (N=65) of students from a large introductory chemistry class. Data was examined using elements of grounded theory. Three dimensions were found, Continuous to Discrete, Interpreting Spectra, and Energy/Force, that explain how student thinking about atomic spectra can be characterized. A fourth dimension, Deterministic to Probabilistic, had been discussed in the research before.

Students who exhibited a mastery of discrete energy absorption predominantly were skilled with a difference reasoning, an understanding that the energy values of the spectral lines correlate to differences of energy levels. Students who successfully interpreted spectra did not necessarily have a probabilistic view of electron position, signaling that those two concepts, as least as they were assessed, do not strongly impact each other.

Using grounded methods on ten student interviews, four main types of representation use and conceptual understanding in the topic of atomic spectra were discovered: Literal Reasoning, Threshold Reasoning, Exact Difference Reasoning, and Meta-Reasoning. Threshold reasoning was indicative of an influence of classical ideas of energy absorption, while Exact-Difference reasoning consisted of a full appreciation of the all or nothing discrete absorption process. Advanced students recognized the stark difference of the quantum behavior from their classical understandings. While some classical ideas, such as threshold reasoning, hindered students from fully understanding the quantum nature of bound electrons, other more productive classical ideas, such as energy conservation, Coulombic attraction of the electron to the nucleus, and the spatial model of the atom, strengthened student understanding.

In an exploratory study, data was analyzed from two students who initially struggled with interpreting spectra. Their interaction with a representation designed to scaffold their understanding of spectra was studied, and their successes and obstacles were explored. One student transitioned from a literal type of thinking to an exact difference type of thinking through interaction with the representation. The second student remained holding onto a threshold type of thinking, despite the representation, signaling possible limitations of such curricular tools.

This dissertation highlights the deeply rooted and persistent nature of students' classical ideas as they learn about quantum concepts. Understanding the impact of classical ideas on the learning of atomic energy absorption will help instructors better understand the issues students face and will assist in developing better curriculum to address and challenge students' classical notions.