Final answer:
The dipole moment of a molecule depends on the individual bond dipoles and the molecule's geometry. Homonuclear diatomic molecules have no dipole moment, while heteronuclear diatomic molecules and asymmetrical polyatomic molecules usually do. Symmetrical polyatomic molecules may have no net dipole moment due to the cancellation of individual bond dipoles.
Step-by-step explanation:
The dipole moment of a molecule is determined by its individual bond dipole moments and the molecule's geometry. In diatomic molecules, the dipole moment is straightforward because it only involves two atoms; homonuclear diatomic molecules like Br2 and N₂ have no dipole moment since their electronegativity is the same. By contrast, heteronuclear diatomic molecules like CO and HF have a dipole moment due to the difference in electronegativity between the atoms.
For polyatomic molecules, the symmetry of the molecule plays a vital role. Molecules like CO₂ have individual bond dipole moments that are equal and opposite, thus canceling each other out and resulting in no net dipole moment. Other molecules, such as H₂O, have bond dipoles that do not completely cancel due to their shape and bond angles, leading to a net dipole moment.
Aspects like molecular shape and the distribution of charge due to differences in electronegativity are crucial in determining whether a molecule has a net dipole moment or not. Highly symmetrical molecules often have no net dipole moment, whereas less symmetrical, or asymmetrically shaped, molecules generally have a nonzero dipole moment because their bond dipoles do not cancel out.