Strong Vs. Weak Acids

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Ian Hurst 3L
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Joined: Fri Sep 25, 2015 3:00 am

Strong Vs. Weak Acids

Postby Ian Hurst 3L » Sun Nov 22, 2015 4:55 pm

I read that as the strength of acids increases as you go down the halogen group on the periodic table (HF --> HI). Why is it that even though the molecules are becoming less polar (and have a lower difference in electronegativity) they are increasing in acidic strength?

Annie Qing 2F
Posts: 28
Joined: Fri Sep 25, 2015 3:00 am

Re: Strong Vs. Weak Acids

Postby Annie Qing 2F » Sun Nov 22, 2015 5:17 pm

While it's true that the molecules are becoming less polar as you move from F to I, for example, this also means that the bonds between H and the ion are becoming weaker. Because I is a much larger atom than F, the distance between H and I is also much larger than that between H and F. With a weaker bond, it's easier to remove an H+. Thus, HI, or any molecule with a long bond between H and the ion, is more acidic than HF, or any molecule with a shorter bond.

This idea is summarized on page 11 in the Acids and Bases section in the course reader.
Let me know if this makes sense??


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