Hexavalent - 1-2-2013 at 13:41
A question I have asks:
"Which ion is the most stable - HS- or Cl- - and why?"
This is probably a very simple question, but the answer is beyond me 
An initial
thought I had was to do with the size of the ion, but I can't be certain. I also thought that it could be influenced by the charge distribution across
the ion...this would make chloride the more stable as the charge is equal across it, and hydrogensulfide the lesser stable ion due to the presence of
the more electronegative sulfur atom.
Any help would be greatly appreciated.
[Edited on 1-2-2013 by Hexavalent]
chemrox - 1-2-2013 at 21:21
I think you're right
kavu - 2-2-2013 at 00:12
That is the right reasoning. The ion which can accommodate the negative charge better is the more stable one. So basically the weaker lewis base is
the more stabile ion. This is affected by delocalization, size, electronegativity and polarization. So a big, delocation stabilized and rather
electronegative species would be the most stabile ion. One way of looking at this would be through acid-base theory. Given that both ions are
conjugate bases to known acids we can determine their relative stability based on the pKa. Low pKa would indicate the favourability of high
dissociation and thus stability of the conjugate base. This is not always applicable as pKa values are usually measured in aqueous sollutions and
solvation of the ions takes place.
[Edited on 2-2-2013 by kavu]