Which characteristic is true of a polar molecule?

• A. It has an equal distribution of electrons
• B. It has a significant dipole moment due to uneven electron distribution
• C. It does not dissolve in water
• D. It has a symmetrical shape

Answer: (B)

A polar molecule is characterized by having a significant dipole moment, which arises from an uneven distribution of electrons. In a polar molecule, the difference in electronegativity between the atoms leads to one end of the molecule becoming partially negative and the other end becoming partially positive. This creates a dipole moment, which is the measure of the separation of positive and negative charges within the molecule.

For example, in water (H₂O), the oxygen atom is more electronegative than the hydrogen atoms, resulting in an unequal sharing of electrons. This causes the oxygen side of the molecule to become slightly negative while the hydrogen side becomes slightly positive, thus generating a dipole moment. This property of having a dipole moment accounts for many of the unique physical and chemical properties of polar molecules, including their ability to dissolve in polar solvents like water.

The other characteristics listed do not define polar molecules: having an equal distribution of electrons would describe a nonpolar molecule, while the capacity to dissolve in water is indicative of polarity. Lastly, a symmetrical shape typically suggests a nonpolar molecule unless there are significant differences in electronegativity that can create an overall dipole moment.