Does the acid strength of hydrochloric and hydrofluoric acid correlate with the electronegativity of the halides?
You are correct, HCl is a stronger acid than HF. Fluorine is both more electronegative and smaller than chlorine. Because fluorine is more electronegative, the bond between it and the hydrogen is more polar, meaning that the proton would need to overcome a larger coulomb force to separate from the fluorine. In addition, fluorine is a smaller atom, meaning that the addition of an electron has a larger effect on the net charge of the atom. This both makes the fluoride anion (the conjugate base) less stable and it also - once again - increases the coulomb force between the proton and the fluorine. In addition, the coulomb force is even stronger because there is a smaller distance between the two atoms. As a general rule of thumb, as you move down the halogens, the acids become stronger and they form more stable conjugate bases.