[Hanlon]

Can someone give me a brief overview of the Relationship between Electronegativity and Ph? Nothing too fancy, simple so I can just refer to what you said here to figure out Ph's based on the periodic table

[MissPhosgene]

Acidity increases with electronegativity of the atom to which the proton is bound. It also increases going down the periodic table because bond lengths increase.

[orgopete]

For nonmetals, the more greater the nuclear charge, the greater the acidity as you compare groups and periods. You cannot compare diagonally, e.g., F vs S.

For MissP, bond lengths CH4>NH3>H2O>HF. CH4 has the longest bond and is the weakest acid. The key is not the bond length, but the proton-electron pair distance. This is consistent with Coulomb's inverse square law and also consistent with the HX halo-acids. It isn't the bond length of HI that makes it a strong acid, it is the greater proton-electron pair distance that increases the acidity. As the nuclear charge is increased, the electrons surrounding the it are pulled in, therefore HF is the strongest acid in its group and HI in its period. The difference is that as you progress down a period, each additional shell increases its radius. But it isn't the radius that matters, because that would imply CH4 should be the strongest acid.

[MissPhosgene]

The increased radius coincides with increasing acidity, as I stated. Increasing radius implies increasing bond length implies implies increasing distance between electrons and the nucleus of the proton, implies increasing acidity, I just didn't state it flat out because I thought the implications were clear and that the effects of increased Z on withdrawal of electron density were understood.

That is strictly for going down the periodic table, as I stated, maybe not as clearly as I should have. Thank you for pointing that out.