Explain, in terms of electronegativity, why an H-F bond is expected to be more polar than an H-I bond.

Answer 1

The electronegativity of an element measures the ability of that element to attract electrons. The EN for F is 4.0, that of I is about 2.7; thus the electrons of the HF bond are attracted more to the F than to the H. That's also true for HI; however, the I has less EN and it doesn't attract as much so the HI bond is less polar than HF.