One Rule to Rule Them All: Inviting Discussions about Content and Process in Johnstone’s Triangle

Johnstone’s triangle is a useful conceptual tool that is often invoked in the context of discussions about the teaching, learning, and practice of chemistry. Depictions of Johnstone’s triangle found on the Internet and other places sometimes include images at each corner of the triangle - macroscopic, representation, and submicroscopic. In this work, we examine the implications of placing images at the submicroscopic corner by reflecting on the difference between content and process, as well as the nature of the boundaries encountered within and between the corners of Johnstone’s triangle. While some educators may advocate for the practice of placing images at all corners of the triangle, we contend that placing an image at the submicroscopic corner can have unintended consequences that may short circuit student reasoning and lead to misconceptions. We propose “One Rule” - to never place an image at the submicroscopic corner - and offer several suggestions for alternative curricular strategies to facilitate discussions of Johnstone’s triangle with introductory students. The primary focus of this work is to provide a rationale for proposing the “One Rule” and to prompt further discussion and reflection about how different interpretations of Johnstone’s triangle may impact the development of students’ chemical reasoning skills.