Final answer:
The polarity of a molecule is determined by electronegativity differences and molecular geometry. Diatomic molecules with different atoms and polar covalent bonds, like HF, are polar. Molecules like CO2 are nonpolar due to their linear shape which cancels out the polar bonds.
Step-by-step explanation:
The two factors that help determine the polarity of a molecule are electronegativity differences between the atoms and the overall molecular geometry. For diatomic molecules with a single bond, such as HF, the molecule is polar if there is a difference in electronegativity between the two atoms, resulting in a polar covalent bond and a dipole moment. In contrast, a diatomic molecule with two identical atoms, such as O2, is nonpolar due to the lack of electronegativity difference and no dipole moment is present.
When it comes to molecules with more than two atoms, both bond type and molecular shape contribute to the molecular polarity. For example, while both water (H2O) and carbon dioxide (CO2) have polar covalent bonds due to differences in electronegativity, water is polar because its bent shape results in an overall dipole moment. In contrast, carbon dioxide is nonpolar because its linear shape causes the bond dipoles to cancel each other out.