In the differences between Boron and Aluminium, it is given that boron forms stable Borates and Aluminium forms unstable aluminates .

Please explain the stability of the 2 compounds.


Firstly, in both borate and aluminate; oxygen is covanlently bounded to boron and aluminium. Oxygen being more electronagative than any element in group 13 from which boron and aluminum belong to will always have delta (-).

Now, about the stability of both, as you go down the group 3, size increase down the group but positive charge (+3) remain the same, This implies that charge density decrease down the group 3. Charge density is about charge of an ion divided by the square of the ionic radius. Therefore, it implies that the polarizing ability of the metal decreases down the group 3. (This also means that, the metallic potential of Boron is greater than that of aluminium** taking into account polarizing ability***). Therefore, comparing their oxyanion compounds (borates and aluminates )which is stabilize mainly by polarising ability of each of the elements ( boron and aluminium) then, Borates will be more stability than aluminate.

  • $\begingroup$ "This also means that, the metallic potential of Boron is greater than that of aluminium. " this is quite wrong. Al is a metal and B is almost a non-metal. I don't the answer but the reasoning does not make any sense whatsoever. $\endgroup$
    – M. Farooq
    Feb 1 '20 at 6:42
  • $\begingroup$ As used in that contest by my explanation. My argument and explanation centered around Charge density and polarizing ability of Boron which is better/stronger than that of Aluminium. $\endgroup$
    – mojeed01
    Feb 1 '20 at 6:45
  • $\begingroup$ I am against the word stability, because stability itself does not mean anything at all. When someone asks A is more stable than B, what does it mean? Is it thermodynamically stable or is it kinetically stable? Stability itself has no definition, so the question is vague. $\endgroup$
    – M. Farooq
    Feb 1 '20 at 6:48

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