Ammonia (NH_3) and hydrogen fluoride (HF) both have unusually high boiling points due to which type of intermolecular force?

• A. ionic bonding
• B. hydrogen bonding
• C. dipole-dipole interactions
• D. London dispersion forces

Answer: (B)

Verified step by step guidance

1. Identify the types of intermolecular forces present in ammonia (NH_3) and hydrogen fluoride (HF). Both molecules are polar and contain hydrogen atoms bonded to highly electronegative atoms (nitrogen in NH_3 and fluorine in HF).
2. Recall that hydrogen bonding is a special type of dipole-dipole interaction that occurs when hydrogen is directly bonded to nitrogen, oxygen, or fluorine, which are highly electronegative elements.
3. Understand that hydrogen bonding is stronger than regular dipole-dipole interactions and London dispersion forces, which explains the unusually high boiling points of NH_3 and HF compared to other molecules of similar size.
4. Recognize that ionic bonding is not relevant here because NH_3 and HF are covalent molecules, not ionic compounds.
5. Conclude that the unusually high boiling points of ammonia and hydrogen fluoride are due to hydrogen bonding, which is the strongest intermolecular force present in these substances.