Chemistry is often seen as a difficult subject to understand. This book focusses on the triangle model that Alex H. Johnstone developed in the early 1980s. Originally conceived in the context of making chemistry more accessible to a wider range of learners, the model has been applied in almost every area of education in chemistry at all stages of learning. In looking at why chemistry is difficult, there are two central questions. Firstly, does the problem relate to the nature of chemistry and, secondly, does it relate to the way humans gain understanding? Both were found to be important and the answers to the two question were found to be connected. The triangle model arose from sustained research into human learning. The central finding from research is the critical role of working memory and the model rationalises so much evidence from chemistry education research as well as the repeated experiences of teachers of chemistry at all levels. In order to understand chemistry, it is
