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Basic qualitative acid/base question

  1. Jul 29, 2007 #1
    1. The problem statement, all variables and given/known data

    Why does acidity increase as you move down a column in the periodic table?


    3. The attempt at a solution

    It seems to me like the opposite should be true. For one thing, electronegativity is decreasing. And in general it seems like more protons in the nucleus should stabilize an E-H bond.
     
  2. jcsd
  3. Jul 30, 2007 #2

    chemisttree

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    Must be a trick question...
     
  4. Aug 1, 2007 #3
    It was a serious question could you explain what you mean?
     
  5. Aug 1, 2007 #4

    chemisttree

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    Acidity is the ability to either donate a proton (Bronstead-Lowry type, doesn't apply here except for hydrogen itself) or to accept an electron pair (Lewis concept) or a substance that increases the hydronium ion concentration when dissolved in water (Arrhenius concept). The Arrhenius concept is not applicable if the element does not dissolve appreciably in water.

    The Lewis acidity trend follows the electronegativity of the elements which decreases as you move down a column in the periodic table. In addition, the Lewis acidity concept deals with the acceptance of a pair of electrons. If an element were to accept two electrons, it would yield a dianion. Does the stability of dianions increase as you move down a column?
    Lewis acidity usually deals with cations rather than the elements.

    Were you being asked about the acidity of cations as you move down a column?

    Tricksy, tricksy...
     
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