12. Intermolecular Forces

« Previous | Next »

Session Overview

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

Resources

Lecture Slides (PDF - 1.0MB)

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

Problems (PDF)

Solutions (PDF)

Textbook Problems

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

Fritz London

Johannes Diderik van der Waals – 1910 Nobel Prize in Physics

Other OCW and OER Content

« Previous | Next »