This article focuses on the case study of the concept of covalent bonding for 10th grade pupils in France. On the basis of their conceptions and difficulties, didactical engineering has been established that should lead to an improvement in the understanding of this concept. After analyzing the pupils' difficulties, we reflected on the construction of the concept of bonding as it is introduced in 10th grade. We argue that the use of several semiotic registers can promote the assimilation of the concept of covalent bonding. The results show that an approach based on learning games allows pupils to take an active part in the construction of the covalent bonding concept and that the stability of this construction depends greatly on the semiotic registers mobilized.