Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

2. Molecular Representations

Intermolecular Forces

Organic Chemistry

2. Molecular Representations

Intermolecular Forces

Previous problemNext problem

4:18 minutes

Problem 34c,d

Textbook Question

Explain why
c. H₂O (100 °C) has a higher boiling point than HF 120 °C2.
d. HF 120 °C2 has a higher boiling point than NH₃ (-33 °C).

Verified step by step guidance

Step 1: Begin by understanding the concept of boiling point. The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure, allowing the substance to transition from liquid to gas. Boiling points are influenced by intermolecular forces such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces.

Step 2: Analyze part (c) regarding H2O and HF. Both molecules exhibit hydrogen bonding, which is a strong intermolecular force. However, H2O can form up to two hydrogen bonds per molecule due to its two hydrogen atoms and two lone pairs on oxygen, whereas HF can only form one hydrogen bond per molecule because it has one hydrogen atom and three lone pairs on fluorine. This ability to form more hydrogen bonds in H2O results in stronger intermolecular forces, leading to a higher boiling point for H2O (100 °C) compared to HF.

Step 3: Examine part (d) regarding HF and NH3. HF has a higher boiling point than NH3 because HF exhibits stronger hydrogen bonding. Fluorine is the most electronegative element, which makes the hydrogen bond in HF extremely strong. In contrast, NH3 forms hydrogen bonds through its nitrogen atom, which is less electronegative than fluorine, resulting in weaker hydrogen bonds. This difference in hydrogen bond strength accounts for HF's higher boiling point (120 °C) compared to NH3 (-33 °C).

Step 4: Consider the role of molecular structure and electronegativity in determining boiling points. The electronegativity of the atoms involved in hydrogen bonding directly affects the strength of the bond. Fluorine's high electronegativity in HF leads to stronger hydrogen bonds than nitrogen's in NH3, while oxygen's ability to form multiple hydrogen bonds in H2O further enhances its boiling point.

Step 5: Summarize the findings: H2O has a higher boiling point than HF due to its ability to form more hydrogen bonds per molecule, and HF has a higher boiling point than NH3 due to the stronger hydrogen bonds formed by fluorine compared to nitrogen. These differences in intermolecular forces are key to understanding the boiling point trends.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hydrogen Bonding

Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is covalently bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. In the case of H2O, each water molecule can form up to four hydrogen bonds, leading to a higher boiling point due to the increased energy required to break these interactions.

Molecular Polarity

Molecular polarity refers to the distribution of electrical charge across a molecule, which affects its physical properties, including boiling point. HF is a polar molecule, but its boiling point is influenced by the strength and number of hydrogen bonds it can form compared to H2O. Despite HF having a higher molecular weight, the extensive hydrogen bonding in water results in a higher boiling point.

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between neighboring particles (atoms, molecules, or ions). These forces include hydrogen bonds, dipole-dipole interactions, and London dispersion forces. The boiling point of a substance is directly related to the strength of these forces; stronger intermolecular forces result in higher boiling points, as seen when comparing HF and NH3.

Watch next

Master How IMFs are related to melting and boiling points. with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

N-Methylpyrrolidine has a boiling point of 81 °C, and piperidine has a boiling point of 106 °C.

b. Tetrahydropyran has a boiling point of 88 °C, and cyclopentanol has a boiling point of 141 °C. These two isomers have a boiling point difference of 53 °C. Explain why the two oxygen-containing isomers have a much larger boiling point difference than the two amine isomers.