Plots in Figure 1 depict the one-electron radial density distribution for pairs of adjacent atoms (ions) within the He-isoelectronic series in its ground-state.On the contrary, the one-particle radial density distribution of the Li^(+1)  does not extend to the Light blue zone, as shown in Figure 1 (a).The Light blue zone is part of the one-particle radial density distribution of the He atom.The higher the peak's value, the denser the electronic cloud will be: 
[?D(r)?_max ]_He< [?D(r)?_max ]_(Li^(+1) )< [?D(r)?_max ]_(Be^(+2) )  [r_0 ]_(Be^(+2) )  >[r_0 ]_(B^(+3) )  >[r_0 ]_(C^(+4) )  >[r_0 ]_(N^(+5) )  >[r_0 ]_(O^(+6) )
        Plots Figure 2 and 3 represent three and two dimensions, respectively.The contour plot is produced by slicing the three-dimensional plots of the D(r_1,r_2 )  into definite slices.The observation that the red region of the Li^(+1) ion covers the region from ?D(r_1,r_2)?_max  down to D(r_1,r_2 )=1.80 and the red region of the N^(+5) ion extends from ?D(r_1,r_2)?_max down to D(r_1,r_2 )=11confirms this phenomena.However, the shrinkage in the orbital size will be compensated by producing a denser electron cloud near the nucleus.The first characteristic is the inability of the electron density to extend the nucleus.This is a direct consequence of the properties of any well-defined wavefunction in quantum mechanics.Therefore, the contour plot is a projection of the three-dimensional plots onto a two-dimensional plane defined by r_1  and?Another way, at high atomic numbers, the nucleus draws the electron cloud inward and toward itself.r?_2.see Figures 4 and 5.