In this paper, we explore the use of concept maps (Cmaps) as instructional materials prepared by teachers, to foster the understanding of chemistry. We choose fireworks as a macroscopic event to teach basic chemical principles related to the Bohr atomic model and matter-energy interaction. During teachers' Cmap navigation, students can experience a sense of disorientation, which is detrimental to the learning process. Two graphical cues were tested as Cmap navigation guidance: (1) colour-coded concepts, to group similar content and (2) numbered propositions to offer a reading sequence. A quasi-experimental pre-test-post-test design combined with mental effort was utilized to measure the efficiency of Cmaps in learning. First-year undergraduate students (n = 85) were randomly assigned to study one of four possible Cmaps. The results showed that all students were able to increase their level of factual knowledge, despite the Cmap being used as an instructional material. The lack of cues impaired conceptual understanding. Signalling similar content using colours was critical to reduce the invested mental effort and foster understanding about chemical concepts.