Outer-shell orbital radius

Soft Low-charge density Large ionic radius Easily excited outer shell electrons Cu+ High polarizability Low electronegativity Low-energy vacant orbitals Easily oxidized RSH, RS-, CN", CO... 

The 3d orbitals in TM ions have a relatively large radius and are unshielded by outer shells, so that strong ion-lattice coupling tend to occur in TM ions. As a result, the spectra of TM ions present both broad (S > 0) and sharp (S 0) bands, opposite to the spectra of (RE) + ions, discussed in section 6.2.1, which only showed sharp bands (S 0). 

With this structure the nickel atom lias achieved the krypton electron configuration its outer shell contains five unshared pairs (in the five M orbitals) and five shared pairs (occupying the 4s4p3 tetrahedral bond orbitals). The Ni—C bond length expected for this structure is about 2.16 A, as found by use of the tetrahedral radius 1.39 A obtained by extrapolation from the adjacent values in Table 7-13 (Cu, 1.35 A Zn, 1.31 A). 

A spectroscopic study of Eu -Br showed that the increase in the Br concentration causes a larger enhancement in the intensity and band area of the -> transitions than for the Fj -> transitions. These modifications in the spectra were attributed to changes in the structure and nature of the inner solvation sphere of Eu in the excited state as compared to that of the ground state (Marcantonatos et al. 1984). The differences in intensity between absorption and emission bands would, therefore, reflect formation of inner-sphere complexes by Br in the excited state while outer-sphere complexation would dominate the ground state. It was proposed (Marcantonatos et al. 1981, 1982) that excitation of Eu " ion to the state would result in an expansion of the 4f and a shrinkage of the 5p orbitals with an overall decrease in the metal ion radius. The consequent contraction of the iimer shell would be expected to produce more compact and less easily disrupted outer hydration spheres for both ( Dj) Eu(H20)g and ( Di)Eu(H20)g with a possible increase in kobs-... 

For the lanthanides, the rms radii and the 95% density radius are in shell order, i.e., 4d < 4f << 5s < 5p < 5d <<6s. The radial maximum of the 4f is inside that of the 4d, but otherwise the shell order is observed. What is perhaps not obvious from these plots is that the radial maximum of the 6s is outside the 95% density radius of the 5p shell, whereas the radial maximum of the 5d is inside the 95% density radius of the 5p shell. If the radial maximum is taken as some measure of where the midpoint of a bond would be, this indicates that bonding with the 6s does not incur much repulsion of the ligand orbitals by the outer core (5s and 5p) of the lanthanide, whereas there would be somewhat more repulsion from bonding with the 5d. In any case, the 5d is substantially inside the 6s on all measures of radial extent. 

Variation of atomic radii within a group of the periodic table. We have already established that electrons in the outermost shell of an atom are significantly screened by those in inner shells. Thus, for atoms closer to the bottom of the group, the outer electrons occupy orbitals that extend over much larger distances, and we expect the radius of an atom to increase from top to bottom within a group. 

---