This paper is a systematic contribution to Pedagogical Content Knowledge (Shulman, 2004) on teaching atoms in Chemistry. We justify our normative starting points (we call them “axioms”) and proceed
o from axiom #1 – science education’s foremost goal is comprehension,
o to axiom #2 –comprehension can exclusively be achieved by an individual, be it the teacher or the learner,
o then further to axiom #3 and #4 – on the part of the teacher, both her understanding of the subject matter (content) and of learning (its process and perspective) can be expected to lend considerable importance to the way she designs and organizes teaching & learning situations in school science (axiom #3), – on part auf the learner teachers must presuppose a will to learn (axiom #4)),
o and finally come to axiom #5: Any teaching any design of teaching & learning situations in school science must take concordant to contemporary science.
In this justification process we discovered that the different understandings of comprehension found empirically by Helmstad (1999) correspond neatly to the different didactical approaches of teaching atoms, i.e. the particulate nature of matter. These findings enable both teachers and curriculum designers to make theoretically better founded choices.