Mendeleev and Bohr were both interested in different aspects of structure in the physical world. Describe briefly how each of them used structure to help make their most important discoveries, Mendeleev in chemistry with his periodic table, Bohr in atomic physics with his model of the atom. What, in particular, did Bohr's model have to do with light? Can you think of another physicist we have studied who also used light as the basis for his model of the nature of matter? How would you compare the two?