AS Chemistry
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Hi, for Group IV oxides the general trend is acidic at the top to amphoteric at the bottom. However, what is the reason for this trend?
Ulex writes ...
As with anything in chemistry which involves the question 'Why does something happen rather than something else' the answer is in the energy involved, or rather in the way this energy influences the entropy changes.
We must try to think of all possibilities being available for all the elements of Group IV. The one which actually happens is the one which involves the greatest increase in total entropy; usually this is the one for which the enthalpy change is the most exothermic. Where two possible routes have similar entropy changes, both can happen according to the conditions. At the top of the group the tendency to form simple ions such as C2+ is energetically unfavourable but the formation of complex ions such as CO32- is energetically favourable. As you go down the group the increased atomic radius and the increased screening of the nucleus from the outer electrons tends to reverse this favourability or , at least, to make the formation of simple ions such as Pb2+ increasingly possible.
In deciding the actual outcome of reactions, other energetic factors such as hydration of ions and lattice energy also play their part so that the full 'explanation' is bound to be complicated but, in the end, it comes down to entropy!
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updated: 01 June 2007
