11. The Shapes of Molecules

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Session Overview

Modules Bonding and Molecules
Concepts shapes of molecules: valence shell electron pair repulsion (VSEPR), sigma and pi bonds, and octet stability
Keywords bonding electron, nonbonding electron, hybridized orbital, linear combination of atomic orbitals–molecular orbitals (LCAO-MO), valence shell electron pair repulsion (VSEPR), octahedral, square pyramidal, square planar, trigonal bipyramid, polar bond, non-polar bond, planar, see-saw conformation, dipole, refractive index, electrical conductivity, covalent bond, ionic bond, expanded octet, electron domain, lone pair, molecular skeleton, Lewis structure, bonding orbital, sigma bond, pi bond, triple bond, octet rule
Chemical Substances ethylene (C2H4), methane (CH4), carbon (C), acetylene (C2H2), titanium tetrachloride (TiCl4), sulfur hexafluoride (SF6), bromine pentafluoride (BrF5), iodine tetrafluoride (IF4-)
Applications None


Before starting this session, you should be familiar with:

Looking Ahead

Prof. Sadoway completes the Bonding and Molecules module with a session on secondary bonding, permanent and induced dipoles, hydrogen bonding, and polarizability of molecules (Session 12).

Learning Objectives

After completing this session, you should be able to:

  • Determine the shapes of molecules using hybridized orbitals, linear combination of atomic orbitals–molecular orbitals (LCAO-MO), and valence shell electron pair repulsion (VSEPR) theory.
  • Write Lewis structures showing the electron distribution and molecular skeleton of compounds.
  • Classify each electron as a bonding electron (B) or nonbonding electron (NB).
  • Contrast the properties of covalent bonds and ionic bonds.


Book Chapters Topics
[Saylor] 9.1, "Predicting the Geometry of Molecules and Polyatomic Ions." The VSEPR model; using the VSEPR model; molecular dipole moments

Lecture Video

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Lecture Slides (PDF - 1.2MB)

Lecture Summary

Prof. Sadoway discusses the following:

  • Hybridized bonding in molecules
  • Valence shell electron pair repulsion (VSEPR)

He re-emphasizes the underlying point of this unit: equal bond energies imply equal spatial disposition, and electronic structure dictates bond disposition, which further dictates molecular architecture.


Problems (PDF)

Solutions (PDF)

Textbook Problems

[Saylor] Sections Conceptual Numerical
[Saylor] 9.1, "Predicting the Geometry of Molecules and Polyatomic Ions." 1, 3, 7, 14 none
[Saylor] 9.4, "Polyatomic Systems with Multiple Bonds." 1 none

For Further Study

Other OCW and OER Content

Content Provider Level Notes
5.111 Principles of Chemical Science MIT OpenCourseWare Undergraduate (first-year)

Lecture 15: Valence Bond Theory and Hybridization

Lecture 16: Thermochemistry


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