Ask A Scientist© Chemistry Archive

 
name       Shifaan
status     student
age        19

Question - Some elements are amphoteric and others are not. What makes
elements such as aluminum and lead amphoteric. Is it anything to do with
electron configuration or anything like that. My teacher said that it is
just a fact. Could it be so?


Recall that saying an element amphoteric means that it is possessing both
basic and acidic properties, that it is one which is capable of yielding
both "hydrogen" and hydroxyl ions (assuming aqueous, or similar, chemistry).
This behavior is common in hydroxides of elements of intermediate
electronegativities and relatively high oxidation numbers, such as those
found near the stepped bold diagonal line of the periodic table (including
the Al and Pb you cited). Let's look at aluminum hydroxide, a hydrated
species in solution. [Al(H2O)3(OH)3] This compound will solubilize in
strong acid or base (but not much in neutral solution) by virtue of its
amphoteric nature. In strong acid, it reacts with "hydrogen" (or hydronium
ion) to become the soluble ion [Al(H2O)4(OH)2]+, and will proceed to
[Al(H2O)6]3+, also soluble. In strong base, it "accepts" hydroxyl ion (OH-)
to yield the soluble species [Al(H2O)2(OH)4]-. Yes, this is related to the
electronic configurations of the amphoteric elements, since the reaction
properties (tendency to gain, lose or share an electron) arise from electron
configuration.
Tim Spry
=========================================================