Final answer:
Sommerfeld's atomic model introduced elliptical orbits and a second quantum number l to explain fine structure and correlate with periodic table placement.
Explanation:
Sommerfeld's atomic model expanded on Bohr's original model by introducing the concept of elliptical orbits for electrons. To explain fine structure, Sommerfeld proposed that the orbits could be elliptical and introduced a second quantum number, l, to indicate the degree of ellipticity. This innovation helped provide correlation with the placement of elements in the periodic table.
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