This paper reports the results of applying a particular analytical perspective to data from an interview study: a typology of learning impediments informed by research into learning and students' ideas in science. This typology is a heuristic tool that may help diagnose the origins of students' learning difficulties. Here it is applied to data from students interviewed about a problematic curriculum topic - the ?oribital?

College level students are expected to be able to make sense of, and explain, aspects of chemical bonding and structure in terms of molecular orbital concepts. The present paper derives from in-depth research into the thinking of a small sample of college chemistry students. This study in one UK college revealed the ways in which students found the orbital concept problematic. A previous paper (i?Conceptualizing quanta: illuminating the ground state of student understanding of atomic orbitalsi?) reports how these students struggled to make sense of atomic structure in orbital terms.

This paper presents and discusses data relating to student understanding of the orbital concept and related ideas at college level (i.e. between secondary and university level education). The data derives from in-depth research into the thinking of a small sample of U.K. students. Students enter this level of study having been explicitly taught a quantum theory of matter (i.e. the particle model), and implicitly introduced to the quantization of charge.