A permanent dipole occurs in molecules that have a significant difference in electronegativity between their atoms, leading to an uneven distribution of electron density. This creates a positive end and a negative end within the molecule, resulting in a dipole moment. Common examples of molecules with permanent dipoles include water and hydrogen chloride. Permanent dipoles play a crucial role in determining the physical properties of substances, such as boiling and melting points. They also influence interactions between molecules, including hydrogen bonding and dipole-dipole interactions, which are essential in various chemical and biological processes.