Química

Some Theorical Thoughts.Up to this point I have the facts before you. Now, I am timorously and reluctantly going to propose some “explanations”. Unfortunately, there are no“one-explanation-fits-all” approaches in inorganic chemistry. And really we are dealing with rationalizations rather than explanations.
For the diagonal relationship of ions (lithium with magnesium, beryllium withaluminum), one parameter that fits observed behavior is charge density, the ratio of ion charge to ionic volume (14). The charge density of lithium (98 C mm-3) is much closer to that of magnesium (120 C mm-3)than to the values for the other alkali metals (all less than 25 C mm-3). Though one can always find parameters (such as charge-radius ratio) that also fit some of the time, charge density seems tooffer a wider range of matches of chemical behavior (Rayner-Canham, G. W., manuscript in preparation). For example, we noted above the linkage between calcium ion and lanthanum ion, whose chargedensities are quite close (allowing for variations in radii values) at 52 and 72 C mm-3, respectively. However, it is difficult to explain the resemblance in chemical behavior of predominantly covalentlybonded boron and silicon.
The similarities of the (n) and (n+10) elements in their highest oxidation stare is, in the overall picture, explicable in terms of the matching electron configurationsand, because of the contractions across the transition metal series, almost identical ionic radii (86 and 88 pm, respectively)-and of course, with the same charge, nearly identical charge densities.For aluminum ion and scandium ion, there is an even greater match in properties because they have consecutive noble gas configurations as well as identical charges. The challenge arises when we try toexplain similarities in the covalently bonded compounds of pairs of elements. For example, why do phosphorus and vanadium matching compounds of the type X4O124-1? We do not have a fundamental...