Recebido em 5/3/12; aceito em 15/9/12; publicado na web em 1/2/2013The atomic shell structure can be observed by inspecting the experimental periodic properties of the Periodic Table. The (quantum) shell structure emerges from these properties and in this way quantum mechanics can be explicitly shown considering the (semi-) quantitative periodic properties. These periodic properties can be obtained with a simple effective Bohr model. An effective Bohr model with an effective quantum defect (u) was considered as a probe in order to show the quantum structure embedded in the Periodic Table. u(Z) shows a quasi-smoothed dependence of Z, i.e., u(Z) ≈ Z 2/5 -1.