How does electronegativity affect the polarity of the bond between two atoms?

If two atoms have exactly the same electronegativity the electron density of the two shared electrons in the bond will be shared equally. If the two electrons have different electronegativities then the atom with the greater electronegativity will pull more of the electron density the its side of the bond, creating a negative polarity on that side of the bond leaving a positive polarity on the other side of the bond.

Electrons have a negative charge and so are attracted to the atoms that have a greater pull for electrons or electronegativity. When there is more electron density on one side of the bond than the other that means there is more negative charge on the side of the bond with the greater electron density. The negative charge due to the greater electron density creates a negative polarity creating a more polar bond.

If the difference in electron negativity exceeds 1.7 the bond becomes ionic. The electron density is so concentrated on the side with the greater electronegative that the two atoms are easily separated and act more as ions than a molecule.

So differences in electronegativity create polarity in the bonds between two atoms.