I am sad to relay that Alex Johnstone died just before Christmas at age 89. I have written a short tribute to him because although I never knew him, he helped me make sense of why most of the time we fail, and that when we succeed... it is a triumphal moment!
three levels of representation
This past summer our conversations turned to, “How can we improve our instruction to try and prevent the initial misunderstanding?” We had all read Dorothy Gabel’s article Improving Teaching and Learning Through Chemistry Education Research: A Look to the Future. We were intrigued by the author's description of the three fold system of representing concepts in chemistry.