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12. Intermolecular Forces

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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
[A&E] 11.2, "Intermolecular Forces." Dipole-dipole interactions; London dispersion forces; hydrogen bonds
Amazon logo [JS] 2.5, "The Secondary, or van der Waals, Bond." Van der Waals bonding; permanent and induced dipoles; hydrogen bridge

Lecture Video

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Resources

Lecture Slides (PDF - 1.0MB)

Transcript (PDF)

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

[A&E] Sections Conceptual Numerical
[A&E] 11.2, "Intermolecular Forces." 9, 11, 14, 20, 24 none

For Further Study

Textbook Study Materials

See the [A&E] companion website from Pearson for PowerPoint outlines of each chapter, plus online quizzes, interactive graphs and 3D molecular animations:

Supplemental Readings

Amazon logo Gavroglu, Kostas. Fritz London: A Scientific Biography. New York, NY: Cambridge University Press, 1995. ISBN: 9780521023191.

Amazon logo Israelachvili, Jacob. Intermolecular and Surface Forces. New York, NY: Academic Press, 1992. ISBN: 9780123751812.

People

Fritz London

Johannes Diderik van der Waals1910 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

 

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