Bohr's model of the atom is considered to be important by general chemistry textbooks. A shortcoming of this model was that it could not explain the spectra of atoms containing more than one electron. To increase the explanatory power of the model, Sommerfeld hypothesized the existence of elliptical orbits. This study aims to elaborate a framework based on history and philosophy of science and formulate suggestions for facilitating students' understanding of models in chemistry. Four educational implications emerged: (i) Sommerfeld's innovation introducing elliptical orbits helped to restore the viability of Bohr's model; (ii) Bohr-Sommerfeld's model went no further than the alkali metals, which led scientists to look for other models; (iii) scientific models are tentative in nature; and (iv) inclusion of the Bohr-Sommerfeld model in textbooks can help students understand how science progresses. (Contains 1 figure.)