In reality the splitting of n levels is more severe, as shown on the red background on the previous page. From n = 3 onward, each n level overlaps with the next, and the order of increasing energies is more involved: 3s, 3p ; 4s, 3d, 4p, - - . This is not as complicated as it first appears. If the orbitals are written in a triangular array as opposite, the order of increasing energy is indicated by the diagonal colored arrows. As we shall see in the next section, this sequence of energy levels in an atom provides a complete explanation of the observed structure of the periodic table.

The results of the qualitative treatment of wave mechanics in this section are three essential pieces of information about electrons in atoms: (1) quantum numbers (n, l, m) and their relationships among one another, (2) the electron probability clouds for each (n, l, m) orbital, and (3) the energy levels corresponding to different (n, l, m) orbitals.