HBrO2 vs HClO2

[vanessas0123]

Why is HClO2 more acidic than HBrO2?

I initially thought HBrO2 was more acidic as it has a larger atomic radius (negative charge more dispersed --> more stable ... etc). However, Cl is more electronegative than Br, which makes it more acidic. When would you look at atomic radius vs electronegativity?

[Sydney Jacobs 1C]

Look at atomic radius for binary acids (like HBr vs HCl). Since Br is larger, the bond is longer and therefore weaker, so H is more likely to be removed. HBr would be the stronger acid. However, for oxoacids in which the number of oxygens are the same, look at electronegativity. Since Cl is more electronegative, it will pull electron density away from the O-H bond, weakening the bond. H is more likely to be removed, and HClO2 is the stronger acid. Hope that helps!