Final answer:
The bond character between two atoms shifts from covalent to more ionic as the electronegativity difference between them increases. This higher difference leads to an uneven distribution of electron density and can result in the formation of ions.
Step-by-step explanation:
As the electronegativity difference between two atoms becomes larger, the nature of the bond between them shifts from covalent to more ionic. This is because a higher electronegativity difference means that one atom has a significantly greater tendency to attract electrons towards itself than the other atom. This creates an uneven distribution of electron density, with a partial negative charge (δ-) accumulating on the more electronegative atom and a partial positive charge (δ+) on the less electronegative one, leading to the formation of a polar covalent bond. When the electronegativity difference is large enough, the bond becomes predominantly ionic, with the more electronegative atom completely removing an electron from the less electronegative atom, forming ions. An example of this is the bond between sodium and chlorine in NaCl, which has an electronegativity difference of 2.1, leading to the formation of an ionic compound.