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Holly Phaneuf Erskine

Hi Lauren!

You have got some good thinking going on there! I would be happy to have you in one of my classes.

Your only blindspot is that you are thinking only of the bond breaking. You also have to think of the stability of the products, after the bond breaks.

It helps to think of the separation of H from F in terms of Before and After. There are two competing processes; the separation of H from F, and the stability of the products.

You seem a little stuck in the before picture, which asks, how easy is it to separate H from F? You were right the first time when you guessed it would be easy, since F is so electronegative compared to Cl, Br, or I.

The after picture is just as important, and a competing factor. This asks, how stable are the products, H+ and F-?

F- is very unstable. It does not like to be on its own. This is because charge of one flavor does not like to be forced into a small area. It repels itself! F is a very small atom.

If you put the same amount of charge on a Cl atom, it has more room to spread out and be comfortable, so to speak. So a Cl- ion is more likely to persist and be stable than a F- ion.

For every reaction, judging whether it can happen involves looking at the energies (stabilities) of both the reactants AND the products.

Good thinking!
Holly

Lauren

but oh wait is HF not a strong acid because the such high electronegativity of fluorine and thus such strong bond makes the first ionization energy so high. so yes its a small atom and the bond is really strong but the bond is so strong that it wont readily dissociate like strong acids need to. As opposed to iodine which is bigger in size but still has that polarity with hydrogen but the ionization energy is lower so the hydrogen is more easily removed

Lauren

ok so if Fluorine is smaller than iodine then shouldn't it have a stronger bond with the hydrogen because the positives and negatives are closer. So then the fluorine should be able to attract the shared electrons better. If this is the case then the electron density on the hydrogen would be heavily decreased and then the hydrogen would be able to be easily removed thus making a strong acid. Please let me know where I am not understanding.

5036 Student

Thanks Dr H! It all makes sense now :) xx

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