This study is framed within social semiotic perspectives on multimodality, and it has a twofold aim. The primary aim is to analyze the ways in which teachers draw on different semiotic resources when introducing a new scientific concept in secondary school science classrooms, and to link the results to modal affordance. A secondary aim is to try out parallel analyses of different modes in multimodal meaning making using the ideational meta-function of the SFL framework. Analyses are based on instructional episodes when chemistry teachers introduced the atom as a scientific phenomenon. The main focus of the analyses is on processes used in different modes and how these depict the atom as either static or dynamic. The framework proved fruitful, and analyses revealed important patterns as to what aspects of the atom were given through what mode(s), something which could partly be linked to modal affordance. The results are discussed in relation to its implications for research and education.