What type of intermolecular force exists between the permanent dipoles of two polar molecules?
The correct answer and explanation is:
Correct Answer: Dipole-dipole forces
Dipole-dipole forces are a type of intermolecular force that occurs between two polar molecules. A polar molecule has regions of partial positive and partial negative charges due to an uneven distribution of electrons. This happens when atoms with different electronegativities form bonds, causing one end of the molecule to attract electrons more strongly than the other.
When two polar molecules approach each other, the positive end of one molecule is attracted to the negative end of another. This interaction is what defines a dipole-dipole force. It is an electrostatic attraction between the oppositely charged ends of permanent dipoles in different molecules.
Dipole-dipole forces are generally stronger than London dispersion forces, which are present in all molecules but are especially significant in nonpolar substances. However, dipole-dipole forces are weaker than hydrogen bonding, which is a special and stronger type of dipole-dipole force that occurs when hydrogen is bonded to highly electronegative atoms such as nitrogen, oxygen, or fluorine.
The strength of dipole-dipole forces depends on the magnitude of the dipole moments and the orientation of the molecules. Molecules with larger dipole moments will have stronger dipole-dipole attractions. Also, when molecules are oriented so that their dipoles are aligned optimally, the attraction is stronger.
Dipole-dipole forces play a critical role in determining the physical properties of substances such as boiling point, melting point, and solubility. For example, polar molecules that experience strong dipole-dipole interactions tend to have higher boiling points than nonpolar molecules of similar molecular mass. These forces are also important in biological systems, where polar molecules interact in precise and essential ways to maintain structure and function.