3. A Bit of Electronic structure a) Revisiting atomic structure: What are the four quantum numbers for indicating the electronic states in an atom? b) Schematically draw and label the relative spacing of electronic levels in a hydrogen atom with the ground state at the bottom. c) Derive the energy dependence of the density of states for a free electron gas in 2D. How does this differ from the density of states of the free electron gas in 3D