American Chemical Society (ACS) Chemistry Practice Exam

A polar molecule is characterized by a net dipole moment, which arises from an uneven distribution of charge within the molecule. This uneven charge distribution typically occurs when there are significant differences in electronegativity between the atoms involved in bonding. As a result, one end of the molecule acquires a partial negative charge, while the other end acquires a partial positive charge. This creates a dipole, where there is a distinct separation of positive and negative charge, leading to the molecule being polar.

The other statements do not accurately capture the essence of polar molecules. For instance, stating that a polar molecule contains no charges on any atoms or has an equal distribution of charge contradicts the very nature of polarity, which is defined by the presence of a charge difference. Furthermore, while many polar molecules do contain nonmetals, being composed entirely of them is not a requirement for polarity; it is the charge distribution that fundamentally determines if a molecule is polar or nonpolar.