How many quantum numbers are used to describe the energy state of an electron in an atom?

n = 2, l = 0, ml = 0, ms = -1/2 Only the radial function R(r) of the Schrodinger wave function (psi) is needed to calculate the Energy. The radial function only deals with the principle quantum number (n). Therefore, only n is required to find the Energy. As to find the Energy states, one must specify if we are dealing with a one-electron atom situation or multiple-electron system. For one-electron atoms, the Energy states is determined by the principle quantum number (n). For multi-electron systems, the Energy states depend on both the principle quantum number (n) and orbital quantum number (l). This explanation is valid unless we are using very high resolution spectroscopic techniques, deviations will appear.