Why is the partial charge on a hydrogen atom bonded to a highly electronegative element more concentrated than for any other element?
Hydrogen atoms are very small (with an atomic radius of about 37 pm, they’re smaller than any other atom but helium). So when a bonded electronegative atom pulls electrons away from the hydrogen atom, the positive charge that results is tightly concentrated. The small size of the hydrogen atom is one factor responsible for the unusual strength of the dipole-dipole interaction we call “hydrogen bonding”. When gauging the strength of intermolecular attractions, considering the magnitude of partial charges isn’t enough; you also must look at how spread out the charges are. The atomic radius trends you’ve learned are often very helpful here.
