Session Overview
| Modules | Bonding and Molecules |
| Concepts | ionic bonding: octet stability by electron sharing, energy of ion pairs vs. ion lattice, and properties of ionic crystals, enthalpy of reaction: Hess's law, Born-Haber cycle |
| Keywords | Born exponent, cation, anion, covalent bond, ionic bond, valence shell electron pair repulsion model (VSEPR), interionic separation, crystal array, omnidirectional bond, unsaturated bond, Avogadro's number, electrostatic energy, ionic solid, Madelung constant, melting point, boiling point, electrical insulator, hardness, brittle, soluble, polar solvent, noble gas, ionic liquid, photon, transparency, binding energy, hybridized bond, elasticity, enthalpy, ionization energy, sublimation, electron affinity, lattice energy, bonding electron, nonbonding electron, molecular architecture |
| Chemical Substances | sodium chloride (NaCl), manganese (Mn), sodium (Na), potassium (K), silver iodide (AgI), neon (Ne), magnesium oxide (MgO), aluminum (Al), aluminum oxide (Al2O3), cryolite (Na3AlF6) |
| Applications | design of thermal abrasion resistance materials, design of inert anode materials |
Prerequisites
Before starting this session, you should be familiar with:
- Octet stability and what it means in terms of shell filling; ionic bonding and its formation as a result of Coulombic attraction between a cation and an anion (Session 7)
Looking Ahead
Prof. Sadoway discusses the shortcomings of ionic bonding and Lewis's concept of shell filling by electron sharing including the Lewis dot notation (Session 9); and returns to the valence shell electron pair repulsion (VSEPR) model in Session 11: The Shapes of Molecules.
Learning Objectives
After completing this session, you should be able to:
- Describe quantitatively the energetic factors and characteristics involved in the formation of an ionic bond.
- Understand the valence shell electron pair repulsion (VSEPR) model.
- Sketch the potential energy as a function of inter-ionic separation.
- List the properties of ionic crystals, and relate them to the lattice energy.
- Explain what features of a crystal are reflected in its Madelung constant.
- Understand that the energy change in chemical reactions is path independent.
- Define electron affinity.
Reading
Archived Lecture Notes #1 (PDF), Sections 6, 7
Archived Lecture Notes #2 (PDF), Sections 1, 2
| Book Chapters | Topics |
|---|---|
| [Saylor] 7.3, "Energetics of Ion Formation." | Ionization energies; electron affinities; electronegativity |
| [Saylor] 8.1, "An Overview of Chemical Bonding." | Review of chemical bonding; comparison of covalent and ionic bonds |
| [Saylor] 8.2, "Ionic Bonding." | Electrostatic attraction and repulsion; potential energy at the bond distance |
| [Saylor] 8.3, "Lattice Energies in Ionic Solids." | Calculating lattice energies; the relationship between lattice energies and physical properties; the Born-Haber cycle; predicting the stability of ionic compounds |
| [Saylor] 12.5, "Correlation between Bonding and the Properties of Solids." | Ionic solids; molecular solids; covalent solids; metallic solids |
Lecture Video
> Download from iTunes U (MP4 - 214MB)
> Download from Internet Archive (MP4 - 214MB)
Resources
Lecture Summary
In this lecture, Prof. Sadoway discusses the following topics:
- Energetics of pair attractions
- Energy gained upon converting a gas of ion pairs to a crystal array
- Attraction energy
- Madelung's constant
- Transparent materials
- Hess's Law – energy change in a chemical reaction is path independent
- Hybridized bonding in molecules
This lecture also introduces the valence shell electron pair repulsion (VSEPR) model, properties of covalent (saturated, directional) and ionic bonds, rules for determining molecular shapes, and the classification of each electron as a bonding electron (B) or a nonbonding electron (NB). Equal bond energies imply equal spatial disposition, and the electronic structure dictates bond disposition, which dictates molecular architecture.
Homework
Textbook Problems
| [Saylor] Sections | Conceptual | Numerical |
|---|---|---|
| [Saylor] 8.3, "Lattice Energies in Ionic Solids." | 7, 9 | 4, 5, 6 |
| [Saylor] 8.4, "Lewis Electron Dot Structures." | 2 | none |
| [Saylor] 8.5, "Lewis Structures and Covalent Bonding." | 3 | 7, 9, 13, 18 |
| [Saylor] 8.6, "Exceptions to the Octet Rule." | 2 | 4 |
| [Saylor] 9.1, "Predicting the Geometry of Molecules and Polyatomic Ions." | none | 1, 5 |
For Further Study
Supplemental Readings
Born, Max. My Life: Recollections of a Nobel Laureate. New York, NY: Scribner, 1978. ISBN: 9780684156620.
Born, Max. Physics in My Generation. New York, NY: Springer-Verlag, 1969.
Born, Max. Atomic Physics. New York, NY: Hafner Publications, 1970. ISBN: 9780486659848.
Stoltzenberg, Dietrich. Fritz Haber: Chemist, Nobel Laureate, German, Jew. Philadelphia, PA: Chemical Heritage Press, 2004. ISBN: 9780941901246.
Charles, Daniel. Master Mind: The Rise and Fall of Fritz Haber, the Nobel Laureate who Launched the Age of Chemical Warfare. New York, NY: Ecco, 2005. ISBN: 9780060562724.
People
Fritz Haber - 1918 Nobel Prize in Chemistry
Max Born - 1954 Nobel Prize in Physics
Other OCW and OER Content
| Content | Provider | Level | Notes |
|---|---|---|---|
| 5.111 Principles of Chemical Science | MIT OpenCourseWare | Undergraduate (first-year) | |
| Chemical Bonds | HyperPhysics: Chemistry | High school |