A Level Chemistry OCR Practice Exam

Which type of intermolecular force is generally the strongest?

1. Van der Waals forces

2. Hydrogen bonds

3. Permanent dipole-dipole forces

4. Induced dipole forces

The correct answer is: Hydrogen bonds

Hydrogen bonds are indeed recognized as the strongest type of intermolecular force among the options provided. This strength arises from the specific nature of hydrogen bonds, which occur when hydrogen is covalently bonded to highly electronegative atoms, such as nitrogen, oxygen, or fluorine. The significant difference in electronegativity between hydrogen and these electronegative partners leads to a strong dipole, creating an attraction between the positively charged hydrogen atom of one molecule and the lone pair of electrons on a highly electronegative atom of another molecule. This interaction is much stronger than other types of intermolecular forces. Van der Waals forces, including both London dispersion forces and dipole-dipole interactions, while very important, do not have the same strength as hydrogen bonds. Permanent dipole-dipole forces arise because of the permanent polarity of polar molecules, but they are also weaker than hydrogen bonds. Induced dipole forces occur due to temporary dipoles created in nonpolar molecules by nearby charged or polar molecules; these forces are transient and considerably weaker compared to hydrogen bonding. Thus, the unique characteristics and interactions involved in hydrogen bonding explain why it is the strongest among common intermolecular forces.