Scerri and Erduran (2002) recently resurrected the question: How is knowledge developed and justified in chemistry? Scerri (2003) denies a role for constructivism in chemical education even though chemistry courses use humanly constructed models to represent sub-microscopic particles. The unobservable nature of most chemistry means that humanly constructed mental imagery is an essential element in chemical descriptions and explanations Scientific models begin life as mental models and help chemists and students develop and learn chemistry. This paper claims a role for history, philosophy and epistemology/ontology in chemical education. The paper argues that most chemical models are negotiated by experts and teachers and are interaction products of prior knowledge and experiences, current problems and evidence and reflect the preferences and commitments of their makers. Thus, constructivism deserves a place in the epistemology and philosophy of chemistry.