Illustrated Glossary of Organic Chemistry

Polar covalent bond: A covalent bond in which the electron density is unevenly shared between the two bonded atoms, due to a difference in electronegativity or due to inductive effects. In general the electronegativity difference must be 0.5 or more before the bond is labeled as a polar covalent bond instead of nonpolar covalent bond.

ΔEN Bonding
Bond Example
0.0 - 0.4
Nonpolar covalent bond
H-C, C-C
0.5 - 0.9
Slightly polar covalent bond H-N, H-Cl
1.0 - 1.3
Moderately polar covalent bond C-O, S-O
1.4 - 1.7
Highly polar covalent bond H-O
1.8 - 2.2
Slightly ionic bond
2.3 - 3.3
Highly ionic bond
Na+ F-

The relationship between electronegativity difference (ΔEN) of bonded atoms and bond polarity.

Ethanol has polar covalent bonds (shown in blue) and nonpolar covalent bonds (shown in red).