electronegativity and acidity across a period

[Oh_Gee]

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can some one explain why that as you go from left to right across a period (row), such as
(H—NH2), water (H—OH), and hydrofluoric acid (H—F), acidity increases? If something is more electronegative, doesn't that mean it'll be less likely to disassociate?

 

[Sed8&Intub8]

It would be more likely to disassociate because the higher electronegative species is pulling electron density away from the hydrogen which is less electronegative. But there are other factors as well, such as stability of the conjugate base.

Also HF is not a strong acid, because it is very small so the H and F are very close together and they have a stronger bond, but HCl, HBr, and HI are strong acids.

 

[Oh_Gee]

thanks!

 

[IslandStyle808]

I think it might have to do with the unequal sharing that is seen in section II pg. 105 of the TBR chemistry book. The more electronegative the atom the H is attached to is, the more electron withdrawing it is. This means less equal sharing of the bond, and this is why the acid is more ready to dissociate.

As Swedish has mentioned, as you go down a row the acid strength depends on atom size more than electronegativity. This is why HF is the weakest in comparison of the other halo acids. Make sure you read about oxyacids because this goes into more depth about electronegativity and increasing acidity.