3.6.2—Electronegativity and bond polarity

Electronegativity is an atom's tendency to attract the shared electron pair in a covalent bond. Equal or nearly equal attraction gives a non-polar bond; unequal attraction shifts electron density towards the more electronegative atom, leaving that end δ− and the other end δ+.

A bond dipole records the direction of this charge separation, with the dipole arrow pointing towards the partially negative end. A larger electronegativity difference gives a more polar bond, but bond polarity is a property of the individual bond before the whole molecular arrangement is considered.

To decide whether a molecule has an overall dipole, identify the polarity and direction of every polar bond, then use the molecular shape to see whether the dipoles cancel. In CH₃Cl they do not cancel, so the molecule is polar; in the symmetric CCl₄ arrangement they cancel, so the molecule is non-polar despite its polar C–Cl bonds.

Do not infer overall molecular polarity from one bond or from the presence of polar bonds alone. Keep δ+ and δ− on the correct atoms, and distinguish a polar bond from a polar molecule whose net dipole depends on three-dimensional arrangement.