A molecule can contain polar bonds without being polar overall. Molecular polarity depends on both bond polarities and molecular geometry.

Molecular dipole

Each polar bond contributes a dipole direction. The vector sum of these bond dipoles determines the molecule's overall electric dipole moment.

A symmetric molecule can therefore have polar bonds whose dipoles cancel, while an asymmetric arrangement can leave a nonzero molecular dipole.

Intermolecular forces

Separate molecules attract and repel one another through electromagnetic interactions weaker than ordinary covalent bonds. Important categories include:

• interactions between permanent molecular dipoles;
• interactions involving ions and polar molecules;
• London dispersion forces, produced by fluctuating and induced electron distributions.

Dispersion forces occur even between nonpolar molecules and generally become stronger for more polarizable electron clouds.

Many weak interactions can matter greatly

An individual intermolecular interaction may be weak compared with a covalent bond, yet a large molecule can participate in many such contacts simultaneously. Their combined effect can strongly influence boiling points, solubility, molecular recognition and biological structure.

Hydrogen bonding is an especially directional intermolecular interaction that deserves separate treatment.