The study investigates secondary students’ understanding of “orbital” and “electron cloud” concepts in different quantum contexts (for values of the ʽprincipal quantum number n = 1 and n = 2) on the basis of their verbal and pictorial representations, evaluating also their consistency. Participants, which were 192 12th-grade students from six urban secondary schools of Northern Greece, represented these two concepts through two corresponding tasks of a paper-and-pencil assessment tool, each of which comprised two parts for verbal and pictorial representations, respectively. Results provide evidence that although students struggle to express verbally the orbital and electron cloud concepts, their competences in the corresponding pictorial representations are relatively better, exhibiting inconsistencies between verbal and pictorial representations. Inconsistencies also exist between representations of the orbital and electron cloud concepts, since students appear to have verbally a better understanding of the electron cloud than the orbital, whereas the opposite holds true for their pictorial representations. Comparing verbal and pictorial representations, the pictorial ones appear to be more consistent tools, whereas a quantum context defined by n = 2 seems to be more challenging for students compared to that of n = 1. Furthermore, an analysis of student profiles leads to their categorization in four classes, providing additional relevant information. Implications for science education are also discussed.
