What characterizes a dipole-dipole interaction?

A dipole-dipole interaction is characterized by the attraction between polar molecules. These molecules have regions of partial positive and partial negative charges due to differences in electronegativity between the atoms involved in their bonds. When two polar molecules come close to each other, the positive end of one molecule attracts the negative end of another, leading to an intermolecular force known as a dipole-dipole interaction.

This type of interaction is significant in determining the physical properties of polar substances, such as boiling and melting points. Polar molecules exhibit this interaction due to their permanent dipoles, which do not occur in nonpolar molecules, where the electron distribution is symmetrical, resulting in no net dipole moment. Similarly, while ionic compounds involve attractions between ions and not dipole-dipole interactions, gaseous molecules may not have strong intermolecular forces when not under conditions that promote interactions like dipole-dipole. Thus, attraction between polar molecules is a defining feature of dipole-dipole interactions.