A molecule is polar when it contains polar bonds (due to electronegativity differences between atoms) and its molecular geometry causes the bond dipoles to not cancel out, resulting in a net dipole moment. A nonpolar molecule either has nonpolar bonds with even electron sharing or symmetrical polar bonds whose dipoles cancel each other out, giving no net dipole moment.

Polar Bonds and Electronegativity

Polar molecules have atoms bonded by polar covalent or ionic bonds where electrons are unevenly shared, creating partial positive and negative charges. The difference in electronegativity between atoms causes this uneven electron distribution, such as in water (H₂O), where oxygen is more electronegative than hydrogen, giving the molecule a polar character with a positive and negative pole.

Molecular Shape and Dipole Moment

The shape of the molecule is critical because the dipole moments from individual bonds must not cancel out for the molecule to be polar. If the shape is symmetrical, like in carbon dioxide (CO₂), the bond dipoles cancel each other, making the molecule nonpolar despite having polar bonds.

Summary for Polarity

• Must have at least one polar bond.
• Must have an asymmetrical shape that does not allow dipole moments to cancel.
• The overall molecule must have a net dipole moment (dipole).

Thus, polarity depends on both the nature of the bonds and the geometry of the molecule, determining the uneven distribution of electric charge within it.