Chemistry can be represented macroscopically, submicroscopically and symbolically. The combination of these three levels constitutes the unity of every physical object in the universe. The study investigates the question of how science teachers engage with all three levels of representation in chemistry when they teach. The findings show that the teachers focused only on the macroscopic and symbolic levels of representation, thus failing to engage with the content at all three levels. These findings have negative implications for the training of preservice and in-service teachers, as well as for curriculum development in South Africa. The challenge that chemistry teachers face in South Africa is to evolve suitable didactic practices to preserve the unity of chemistry at all three levels of representation.