Which intermolecular force is the strongest and occurs when hydrogen is bonded to highly electronegative elements such as fluorine, oxygen, or nitrogen?

• A. Ionic bond
• B. Dipole-dipole forces
• C. Covalent bond
• D. Hydrogen bond

Answer: (D)

Hydrogen bonding is the strongest type of intermolecular force, and it occurs when hydrogen is bonded to a highly electronegative atom like fluorine, oxygen, or nitrogen. These electronegative atoms pull electron density away from hydrogen, giving the hydrogen a significant partial positive charge. Because hydrogen is very small, it can get very close to a lone pair on another electronegative atom in a neighboring molecule, creating a strong electrostatic attraction between the δ+ hydrogen and the lone-pair electrons. This interaction is highly directional and stronger than ordinary dipole–dipole forces, though it is still weaker than covalent or ionic bonds, which act within molecules rather than between them.