How do variations in electronegativity result in the unequal sharing of electrons in polar molecules?
If one nucleus of an atom has a greater attractive force than the other atom, the shared electron pair will be closer to the atom with the greater electronegativity. This causes variations in the polarity in the molecule. The molecule can end up being partially negative, or partially positive. If the two atoms have the same electronegativity, then they are a nonpolar colvalent bond.