Advanced Placement (AP) Chemistry Practice Exam

What condition leads to a larger dipole moment in a molecule?

1. Higher symmetry in molecular structure

2. Greater difference in electronegativity between its atoms

3. Increased number of bonds

4. Absence of polar bonds

The correct answer is: Greater difference in electronegativity between its atoms

A larger dipole moment in a molecule is indeed a result of a greater difference in electronegativity between the atoms that make up the molecule. Electronegativity is the tendency of an atom to attract electrons in a bond; when there is a significant difference in electronegativity between two bonded atoms, the more electronegative atom pulls the bonding electrons closer to itself. This creates partial negative and positive charges on the respective atoms, thereby establishing a dipole. The strength of the dipole moment is directly proportional to both the amount of charge separation and the distance between the charges. Therefore, when there's a greater difference in electronegativity, it enhances the polarity of the bond and increases the dipole moment. In comparison to other options, higher symmetry in molecular structure tends to minimize the overall dipole moment because the individual dipole moments can cancel each other out. An increased number of bonds does not necessarily lead to a larger dipole moment, as these bonds could be non-polar or may cancel each other out in symmetrical arrangements. Lastly, the absence of polar bonds would result in a non-polar molecule, which definitively does not have a dipole moment. Thus, the choice regarding a greater difference in electrone