why are thiols stronger acids than alcohol

I understand that it's because sulfur is a larger atom so the electrons can be more spread out in the conjugate base stabilising it, but sulfur also has more electrons so although the electron density is more spread out it has greater electron density. So in don't understand how this leads to greater stability :confused:

Am I misunderstanding something here?

Reply 1

username878045

17

Sulfur is less electronegative, which would decrease the acidity. However, the bond between sulfur and hydrogen is weaker than that of oxygen and hydrogen (because sulfur is larger) and the negative charge is spread over a larger area as you said. The electrons already on sulfur can largely be ignored - only the negative charge is relevant to stability because that's what would react.

Reply 2

tazmaniac97

OP

12

Original post by PythianLegume

Sulfur is less electronegative, which would decrease the acidity. However, the bond between sulfur and hydrogen is weaker than that of oxygen and hydrogen (because sulfur is larger) and the negative charge is spread over a larger area as you said. The electrons already on sulfur can largely be ignored - only the negative charge is relevant to stability because that's what would react.

But even though the charge is spread over a larger area, wouldn't the fact that there is more charge as there's more electrons outweigh the effect spreading of electrons has? :confused:

Reply 3

username878045

17

Original post by tazmaniac97

But even though the charge is spread over a larger area, wouldn't the fact that there is more charge as there's more electrons outweigh the effect spreading of electrons has? :confused:

But the electrons already on the sulfur atom in lower energy states/shells are mostly uninvolved in reactions because they are held by the nuclear charge of the sulfur, and require too much energy to interact.

Reply 4

tazmaniac97

OP

12

Original post by PythianLegume

But the electrons already on the sulfur atom in lower energy states/shells are mostly uninvolved in reactions because they are held by the nuclear charge of the sulfur, and require too much energy to interact.

So when we talk about spreading of electron density we're only referring to outer shell electrons, so because sulfur has a greater atomic radius the outer shell electrons are further away from eachother. I think I understand now, I was thinking about all the electrons in the atoms :tongue:

Thank you so much for the help :smile:

Reply 5

username878045

17

Original post by tazmaniac97

So when we talk about spreading of electron density we're only referring to outer shell electrons, so because sulfur has a greater atomic radius the outer shell electrons are further away from eachother. I think I understand now, I was thinking about all the electrons in the atoms :tongue:

Thank you so much for the help :smile:

Not further away, just spread over a larger volume. I don't want to confuse you if you've been taught that electrons orbit in rings that resemble concentric circles, but in reality even outer shell electrons could be found very close to the nucleus, they are just more likely to be found in a larger volume/further out.