The Complexity of Reasoning about and with Chemical Representations

External visual representations of chemical entities and processes (chemical representations) play a critical role in chemical thinking and practice. They support reasoning by serving as bridges between the macroscopic world and the chemical models that help us make sense of the properties and behaviors of substances in our surroundings. Consequently, many chemistry education research studies have been carried out to explore and foster students' representational competency in our discipline. Nevertheless, in this Perspective I argue that investigations in this area would benefit from a more in-depth analysis of how the distinctive characteristics of chemical representations affect student reasoning. I identify four dimensions of variation in these representations (iconicity, quantitativeness, granularity, dimensionality) that affect students' ability to interpret, connect, generate, and use chemical representations. I discuss how these features influence the unpacking or packing of information during different types of tasks, affecting sense-making and perceptual competency. Implications for chemistry education research and practice are considered.