Hydrogen Atom
En = -13.6eV/n2 n=1,2,3,…
ground state has E1 = -13.6eV
ionization energy is 0- E1 = 13.6eV => energy needed to remove electron
excited state: n=2 E2 = -(13.6/4)eV
electron must absorb a photon of energy hf= E2 - E1 =hc/? = (3/4)(13.6eV)