Molecular Structure and Acid Strength The strength of an acid depends on how easily the proton, H+, is lost or removed. The more polarized the bond between H and the atom to which it is bonded, the more easily the H+ is lost or donated.We will look now at factors that affect how easily the hydrogen can be lost and, therefore, acid strength.For a binary acid, as the size of X in HX increases, going down a group, acid strength increases.For a binary acid, going across a period, as the electronegativity increases, acid strength increases.Which is a stronger acid: HF or HCl? Which is a stronger acid: H2O or H2S? Which is a stronger acid: HCl or H2S?HF and HCl These are binary acids from the same group, so we compare the size of F and Cl. Because Cl is larger, HCl is the stronger acid.