electronegativity vs. acid strength

[joonkimdds]

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Acid strength:
HI>HBr>HCl>>>>>HF
first three are strong acids and HF is a weak acid

but in organic chemistry,
I3CCO2H vs. F3CCO2H
F3CCO2H is stronger acid and the reasoning was that F is more electronegative than I.

how do I need to distinguish these two different concepts?

 

[PinkDDS]

For HF:

Since F is very electronegative it pulls the H toward itself and it doesn't let H to be removed (remember the definition of a bronsted acid: acid is a proton donor so if F does not let H to be donated then HF is not a strong acid)

For F3CCO2H:

The more electron withdrawing groups make the molecule more Acidic by induction (again pulling the electrons toward itself) and making the conjugate base more stable. The more stable the conjugate base is the more acidic the molecule.

Since F is more electronegative than I, the molecule that contains F is more acidic.

I hope this helps!

 

[drgreen]

Acid strength:
HI>HBr>HCl>>>>>HF
first three are strong acids and HF is a weak acid

but in organic chemistry,
I3CCO2H vs. F3CCO2H
F3CCO2H is stronger acid and the reasoning was that F is more electronegative than I.

how do I need to distinguish these two different concepts?

Firstly, in both cases, F is more EN than I, meaning that it has the ability to attract electrons (or electron density) towards itself in a covalent bond.
BUT, it is also important to remember that atomic radii is coming into play. Atomic radius tends to increase as one proceeds down any group of the periodic table. This makes sense since atoms with more electrons have larger radii. So let's analyze.

HF vs HI:
Since I is farther from H, than F is from H, and since F is more electronegative, H can more easily dissociate from I. the H's are being held onto with less strength by I (Additionally, in terms of acid strength, the more stable an acids conjugate base, the stronger the acid. I- is more stable than F- because it's electrons have more space, and are dispersed better.

I3CCO2H vs F3CCO2H:
Since F is more electronegative than I, it is pulling electron density (termed inductive forces) away from the Oxygens (which are resonance stabilized btw). So instead of focusing on the F's and I's, let's focus on the oxygens now. in F3CCO2H, the oxygens have less electron density than in I3CCO2H, and now the H's are being held onto with less strength by oxygen in F3CCO2H, and have an easier time leaving.

 

[Mamona]

Firstly, in both cases, F is more EN than I, meaning that it has the ability to attract electrons (or electron density) towards itself in a covalent bond.
BUT, it is also important to remember that atomic radii is coming into play. Atomic radius tends to increase as one proceeds down any group of the periodic table. This makes sense since atoms with more electrons have larger radii. So let's analyze.

HF vs HI:
Since I is farther from H, than F is from H, and since F is more electronegative, H can more easily dissociate from I. the H's are being held onto with less strength by I (Additionally, in terms of acid strength, the more stable an acids conjugate base, the stronger the acid. I- is more stable than F- because it's electrons have more space, and are dispersed better.

I3CCO2H vs F3CCO2H:
Since F is more electronegative than I, it is pulling electron density (termed inductive forces) away from the Oxygens (which are resonance stabilized btw). So instead of focusing on the F's and I's, let's focus on the oxygens now. in F3CCO2H, the oxygens have less electron density than in I3CCO2H, and now the H's are being held onto with less strength by oxygen in F3CCO2H, and have an easier time leaving.

Well done now I understand this better.