What does it mean for a molecule to be polar?

A molecule is considered polar when it has an uneven distribution of electron density, which results in partial positive and negative charges within the molecule. This occurs because certain atoms, especially those that are more electronegative, attract electrons more strongly than others, leading to an unequal sharing of electrons in covalent bonds. Consequently, regions of the molecule become slightly positively charged, while other regions become slightly negatively charged.

This dipole moment created by the separation of charges allows polar molecules to interact more readily with other polar substances, influencing properties such as solubility, boiling and melting points, and reactivity. The characteristic of having partial charges is what distinguishes polar molecules from nonpolar ones, which have a more uniform charge distribution.