Session Overview
| Modules | Bonding and Molecules |
| Concepts | secondary bonding, permanent and induced dipoles (London dispersion/van der Waals), hydrogen bonding, polarizability of molecules |
| Keywords | permanent dipole, induced dipole, hydrogen bond, polarity, London dispersion, electronegativity, melting point, boiling point, intermolecular bond, solid, liquid, gas, van der Waals force, secondary bond, dipole moment, polarizability, state of aggregation, Fritz London, Johann van der Waals |
| Chemical Substances | hydrochloric acid (HCl), argon (Ar), iodine (I2), methane (CH4), helium (He), propane (C3H8), octane (C8H18), eicosane (C20H42), hydrofluoric acid (HF), ammonia (NH3), water (H2O) |
| Applications | liquid water supports life; methane sea on Titan; states of hydrocarbons at STP |
Prerequisites
Before starting this session, you should be familiar with prior topics in Bonding & Molecules (Session 8 onwards), especially:
- Periodic trends in electronegativity, atomic radius, and valence energy
- The probability distribution of the electron in an atomic orbital
- Ionic and covalent bonds, and how they determine molecular formulas, shapes, and polarity
Looking Ahead
Water has unusual properties due to its hydrogen bonds, which will be explored further in the modules covering Aqueous Solutions (Session 25, Session 26) and Biochemistry (Session 30 onwards). Experimental data about the state of a material at varying temperature and pressure is summarized in its phase diagram, the topic of Session 33 through Session 35.
Learning Objectives
After completing this session, you should be able to:
- Explain which atoms or molecules experience dipole-dipole interactions, induced dipole-induced dipole interactions, and/or hydrogen bonding.
- Compare the relative strengths of ionic, covalent, and the various intermolecular bonds, and use this information to correlate the bulk properties of a material at various temperatures with the presence or absence of secondary bonds.
- Predict the melting and boiling points of materials based on secondary bonds and polarizability.
Reading
Archived Lecture Notes #2 (PDF), Section 4
| Book Chapters | Topics |
|---|---|
| [Saylor] 11.2, "Intermolecular Forces." | Dipole-dipole interactions; London dispersion forces; hydrogen bonds |
| [JS] 2.5, "The Secondary, or van der Waals, Bond." | Van der Waals bonding; permanent and induced dipoles; hydrogen bridge |
Lecture Video
> Download from iTunes U (MP4 - 148MB)
> Download from Internet Archive (MP4 - 148MB)
Resources
Lecture Summary
Substances in the aggregate may be solid, liquid, or gas at a given temperature and pressure. To predict the state of a substance, both intramolecular (primary bonds: ionic, covalent) and intermolecular forces must be taken into account. Prof. Sadoway discusses the following secondary bond types:
- dipole-dipole (e.g. HCl)
- induced dipole-induced dipole (e.g. Ar, I2, CH4, He), also known as London dispersion forces or van der Waals bonds
- hydrogen bonding (e.g. HF, H2O, NH3)
Homework
Textbook Problems
| [Saylor] Sections | Conceptual | Numerical |
|---|---|---|
| [Saylor] 11.2, "Intermolecular Forces." | 9, 11, 14, 20, 24 | none |
For Further Study
Supplemental Readings
Gavroglu, Kostas. Fritz London: A Scientific Biography. New York, NY: Cambridge University Press, 1995. ISBN: 9780521023191.
Israelachvili, Jacob. Intermolecular and Surface Forces. New York, NY: Academic Press, 1992. ISBN: 9780123751812.
People
Johannes Diderik van der Waals – 1910 Nobel Prize in Physics
Other OCW and OER Content
| Content | Provider | Level | Notes |
|---|---|---|---|
| Properties of Water | HyperPhysics: Chemistry | High school | |
| Intermolecular Forces - Grade 11 | Connexions | High school | |
| 5.112 Principles of Chemical Science | MIT OpenCourseWare | Undergraduate (first-year) |
Start - 25:15 in Lecture 16: Intermolecular Interactions End - 38:15 in Lecture 17: Polarizability |
| 7.012 Introduction to Biology | MIT OpenCourseWare | Undergraduate (first-year) | Lecture 2: Biochemistry 1 |