Determining whether bonds are pure covalent, polar covalent, or ionic?

Chemical bonding ....

All chemical bonding is essentially the same: the nuclei of the bonded atoms attract all of the neighboring electrons.  The the attraction may not be same; one nucleus may have a greater attraction than the other, resulting in varying degrees of "polarness."  The more polar a bond, the more it begins to have the characteristics of a hypothetical "ionic" bond.

"Ionic" and "covalent" are the hypothetical extremes of the bonding continuum and are "ideal bonds."  Real bonds like along the continuum and have characteristics of both.  Therefore, we can describe bonds by the percent ionic character which may be approximated from the electronegativity difference, ΔEN.

..... % ionic character = 100(1 - e^(-ΔEN²/4))

Bond ... % ionic char.

N and Se ... 6% ............ polar covalent

N and N ..... 0% ............ purely covalent

Ca and F ... 90% .......... high ionic character

C and O .....18% .......... polar covalent