acidic protons

[SaintJude]

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Why is the H-attached to sulfur the most acidic proton?

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[chiddler]

Why is the H-attached to sulfur the most acidic proton?

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i think the same reason HI is more acidic than HCl. Because a larger atom size means a more polarizable ion (and thus can hold onto its negative charge better than oxygen) and a longer bond = weaker bond with hydrogen when compared to OH.

 

[SaintJude]

I thought smaller atoms can hold on to their negative charge ions better. If S can hold onto its negative charge better than oxygen, then why is oxygen more elecronegative?

If it helps, the explanation said: "group effect" (Curse those 2-word explanations!!)

 

[chiddler]

I thought smaller atoms can hold on to their negative charge ions better. If S can hold onto its negative charge better than oxygen, then why is oxygen more elecronegative?

If it helps, the explanation said: "group effect" (Curse those 2-word explanations!!)

i don't know what group effect is...do you? this is closest i got with googling

i have a certain understanding of what polarizability is, but i'm not sure of its accuracy. I don't want to confuse you nor feed you wrong info so i can't add more. I do know that a larger atom is more polarizable because it has a larger electron cloud. A larger electron cloud also means that when another atom bonds with it, then the bond will be longer when compared to a bond with a smaller atom.

So a net of two effects: A more polarizable ion meaning it can exist as a charged ion more easily, and a longer weaker bond. Both of these make S more acidic. These are the same reasons HF is a weak acid. F is small and NOT polarizable (does not exist as an ion very well), and because it's so small the HF bond is short and strong.

 

[MedPR]

I thought smaller atoms can hold on to their negative charge ions better. If S can hold onto its negative charge better than oxygen, then why is oxygen more elecronegative?

If it helps, the explanation said: "group effect" (Curse those 2-word explanations!!)

The "group effect" is probably referring to the fact that (as chiddler said), the larger atom will have the more acidic hydrogen when comparing two atoms in the same group. O and S are in the same group, S is larger, therefore its bond with H is longer, therefore the H is more easily donated. Same as HI and HCl.

 

[MT Headed]

Oxygen is more electronegative than sulphur, but annoyingly enough, once you satisfy their needs and give each of them an electron, O- is more unstable than S-. The stability of the ion is easier to understand if you think of oxygen being small and sulphur being large. Oxide just doesn't have anyplace to put the extra electron comfortably, while humogous sulfide hardly notices the extra addition and can distribute this annoying charge through a much larger volume.

I know some of this stuff must seem arbitrary and it probably feels like we are making it all up, but with enough practice I promise you will get it too and these kinds of questions become much easier.

 

[Temperature101]

The "group effect" is probably referring to the fact that (as chiddler said), the larger atom will have the more acidic hydrogen when comparing two atoms in the same group. O and S are in the same group, S is larger, therefore its bond with H is longer, therefore the H is more easily donated. Same as HI and HCl.

I think you have the perfect explanation...Since S is a larger atom, the bond it forms with H will be longer; therefore, it will be a 'weaker' bond than the bond H from with O. The weaker H bond will be easily removed.