Elements with great differences in electronegativity tend to form ionic bonds. Atoms of elements with similar electronegativity tend to form covalent bonds. (Pure covalent bonds result when two atoms of the same electronegativity bond.) Intermediate differences in electronegativity between covalently bonded atoms lead to polarity in the bond. As a rule, an electronegativity difference of 2 or more on the Pauling scale between atoms leads to the formation of an ionic bond. A difference of less than 2 between atoms leads to covalent bond formation. The nearer the difference in electronegativity between atoms comes to zero, the purer the covalent bond becomes and the less polarity it has.

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