[Winga]

HI and HF,

1. HI bond is weaker than HF bond and I- is more stable than F-
2. I- is easier to donate e- than that of F- due to lower electronegativity

Using the first approach will show that HI is more acidic.
However, using the second approach, I- is easier to donate e- pair to proton.
It seems that these two approaches are contradictive to each other (but both are correct), so, how to explain the acidity using both approaches?

[Mitch]

1. HI bond is weaker than HF bond and I- is more stable than F-

Bond strength is defined as a homolytic clevage not heterolytic. Your getting yourself confused here.

[dexangeles]

Bond strength is defined as a homolytic clevage not heterolytic. Your getting yourself confused here.

correct me if I'm wrong Mitch, but if it is a homolytic cleavage, then you would end up with radicals instead of ions, right?

doesn't number 2 only say that I- is more nucleophilic than F- eventhough F- is more basic (because solvation hinders F-)

now im confused too

[Winga]

Bond strength is defined as a homolytic clevage not heterolytic. Your getting yourself confused here.

Therefore, the explanation is that depending the stability of conjugate bases.
I- is more stable than F-. Are there more explanations?

About the 2nd one, e.g. the nitrogen-containing compounds (NH3) is more basic than oxygen-containing compounds (H2O) because of lower electronegativity of nitrogen (easier to donate e- to proton).
This implies that I- is easier to donate e- than that of F-, I- is more basic, but it's wrong.

Basicity:
decreases across the period (due to the differences in electronegativity)
decreases down the group (why? I think it's not depended on electronegativity, but from what factors?)

[movies]

Why would it not depend on electronegativity?

[Demotivator]

Going  left to right the electronegativity increases which polarizes the bond to make it more acidic.
Going down a group, the electronegativity does not increase, yet acidity increases as Winga noted. This is due to decreasing heterolytic bond strength from increasing anion size.

[Winga]

Why would it not depend on electronegativity?

If it depends on electronegativity, F- will become less basic that implies HF is more acidic.

[Winga]

Going  left to right the electronegativity increases which polarizes the bond to make it more acidic.
Going down a group, the electronegativity does not increase, yet acidity increases as Winga noted. This is due to decreasing heterolytic bond strength from increasing anion size.

Does acidity/basicity depend on both electronegativity and bond length/strength across the period and down the group?

Across the period, as the bond lengths of H-C, H-N, H-O and H-F, are similar, so the electronegativity effect becomes the dominant factor, right?

Down the group, as the bond lengths from HF to HI increase significantly, so using the differences in bond strength to explain is prefer to electronegativity, right?

By the way, can we use thermodynamics and kinetics simultaneously to explain the acidity/basicity?

[Mitch]

Does acidity/basicity depend on both electronegativity and bond length/strength...

using the differences in bond strength to explain is prefer to electronegativity, right?

Your banned from from using the term bond strength and acidity in the same sentence.

[Winga]