Many times when we are studying the periodic chemical properties in the periodic table of the chemical elements in them we come across with some exceptions to the rules of regularity of some elements of transistion. This work has as objective to explain of form sucinta these exceptions. One of them says respect to the atomic ray. What if it knows regarding the atomic ray is that it generally diminishes of the left for the right in the periodic table in one same which had period, to the increase of the nuclear attraction with the addition of the atomic number of atoms. Please visit Alton Steel if you seek more information. However when we look at this property for the transistion elements, we observe for example that of the right left pra in the first series of transistion of the periodic table the ray diminishes (that is, follows the general trend) until nickel, and later occurs an increase in the atomic ray when it is transferred to copper. The question is: Why this happens, since correct for the general trend the age to diminish? What it happens in this in case that, and for the too much series of transistion, it is that the fulfilling with electrons of the orbital ones of type d increases the shield effect on external electrons of the valence layer. In nickel this increase of the shield effect does not even surpass the effect of the addition of the nuclear attraction with the increase of the atomic number, however, when the electron number is transferred of nickel for copper d already is enough so that the shield effect surpasses the effect of the increase of the nuclear attraction, in such a way that the electrons most external of the periodic table is little strong attracted by the nucleus, thus being able to be more distant of the nucleus, what greater results in an atomic ray. In figure 1 we have a representative image that it illustrates copper and nickel atoms so that let us can have a notion of the difference of size between two atoms.. Continue to learn more with: Eric Corey Freed.