Acidity question.....

[JohnTulisa]

So based on this question, we are told to rank acidity based on Size when we are comparing atoms within the same group, even though I've always done it based on electronegativity.

HOWEVER,
This question bellow tells us that the more electronegative the atom is, the more acidic it is....... (meaning the smaller the size, the more acidic) which contradicts the answer from Ari.

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[confidentandgood]

For the second question, you should be looking at the inductive effects acting on the remaining ion.

 

[WolfsBane]

So based on this question, we are told to rank acidity based on Size when we are comparing atoms within the same group, even though I've always done it based on electronegativity.

HOWEVER,
This question bellow tells us that the more electronegative the atom is, the more acidic it is....... (meaning the smaller the size, the more acidic) which contradicts the answer from Ari.

the reason that the HI is more acidic is because its bigger and will leave the H more easily while the second question was dealing with a carboxylic acid. the F and Cl in that case are not connected to the H and therefore are able to stabilize the anion through inductive affects therefore making the carboxylic acid with the F more acidic.

 

[rdub]

The Electronegativity of the atom matters when the acidic hydrogen in question is not directly attached to the electronegative atom. This applies in the last example you have, you can see the F and Cl are one carbon away from the acidic hydrogen, but they are not directly attached to it. In this scenario, the electronegative atom can stabilize the charge of the conjugate base. The more electronegative an atom is, the better ability it has to stabilize a negative charge (making it a more acidic acid).

The Size of the atom matters when it is directly attached to the acidic hydrogen in question. So if you have HCl and HBr, you know that HBr is more acidic because Bromine is so much bigger. My professor explained it like this... you have a big fat person and a small skinny person trying to hug each other. The size difference between fat bromine and skinny hydrogen is so drastic that it results in poor orbital overlap, so the bond is weak (meaning it is very acidic). If you have two skinny people hugging, such as H2, then the bond will be strong and non-acidic.

 

[JohnTulisa]

All of you guys are Dentists amongst men! @russelldw where are you applying to school??

 

[rdub]

All of you guys are Dentists amongst men! @russelldw where are you applying to school??

I applied to ten schools all over the country!

 

[JohnTulisa]

Why is the hydrogen on the SP more acidic than the H on Nitrogen? I thought Atom triumph over Orbital. (CARDIO)

 

[rdub]

Why is the hydrogen on the SP more acidic than the H on Nitrogen? I thought Atom triumph over Orbital. (CARDIO)

NH2 is a base. It would rather pick up a hydrogen and become NH3+ than become NH-. This is something you should just memorize and know.
The sp hybrid will gladly take a negative charge because the electrons will be close to the positively charged nuclei (sp hybrid orbitials contain more s character than sp2 or sp3).

 

[confidentandgood]

NH2 is a base. It would rather pick up a hydrogen and become NH3+ than become NH-. This is something you should just memorize and know.
The sp hybrid will gladly take a negative charge because the electrons will be close to the positively charged nuclei (sp hybrid orbitials contain more s character than sp2 or sp3).

Triple bonds are easier to deprotonate in general as an orbital with more s character is a more stable place for remaining electrons. Good rule of thumb! Nitrogen just prefers to be basic (electron-donating) because it is less electronegative than oxygen or fluorine, no?

 

[tommyngu]

I think it might help you to look at the stability of the conjugate base when comparing acidity in each of the cases mentioned in this thread.

 

[0rgansm]

Which practice test is that?
Edit: didn't read Ari, nvm.