Flexi Says: For molecules with more than two atoms, the molecular geometry must also be taken into account when determining if the molecule is polar or nonpolar. If we compare carbon dioxide and water, carbon dioxide (CO2) is a linear molecule. The oxygen atoms are more electronegative than the carbon atom, so there are two individual dipoles pointing outward from the C atom to each O atom. However, since the dipoles are of equal strength and are oriented in this way, they cancel each other out and the overall molecular polarity of CO2 is zero. Water is a bent molecule because of the two lone pairs on the central oxygen atom. The individual dipoles point from the H atoms toward the O atom. Because of the shape, the dipoles do not cancel each other out and the water molecule is polar. In the Figure below, the net dipole is shown in blue and points upward.
