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For 12.51 a, the explanation in the solutions manual is confusing me. I know just by memorization that HCl is a strong acid and HF is not, but why would HF not be stronger if F is more electronegative than Cl (using the logic from part c,d, and f)?
From the textbook, page 485: "The weaker the H-A bond, the stronger the acid. This effect is dominant for acids of the same group" Since F and Cl are in the same group, the one with the weaker bond will be a stronger acid. Cl is less electronegative so it will have a weaker bond and therefore be the stronger acid
electronegativity is NOT a factor in determining bond strength. The only factors are atomic radius and bond multiplicity (i.e. is it a single, double or triple bond). Cl is a larger atom, so the bond length between it and H will be longer than that of F and H, making it a weaker bond, easier to break, and more likely to dissociate in water
The size of atoms on a periodic table increases down a group. In the case of F, it is the smallest atom in the group, which consists of Cl, Br, I, etc. Because it is the smallest atom, when bonded to a hydrogen atom, the bond length is shortest, as the atomic radius is the shortest. Shorter bond lengths mean that the bond is stronger, meaning the F atom will hold on to the hydrogen more tightly and dissociate much less frequently than would HCl, HBr, etc.
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