The goal of this assignment is to explore the competing theories of molecular bonding in use currently. The first model, Valence Bond Theory, is quite useful in most ordinary chemistry scenarios and readily applied to problems without computers. The other model, Molecular Orbital Theory, requires computers to utilize, but the information obtained gives chemists the chance to understand molecules in a way impossible to do so in previous decades.

Chapter 9 introduces us to the competing theories of molecular bonding. Valence Bond Theory is an extension of the rules outlined in Chapter 8, and we will use hybridization to understand how atomic orbitals combine into molecular orbitals along specific axes. We will also look at the more complicated (but more useful) Molecular Orbital Theory. The Four Principles of Molecular Orbital Theory apply to all systems and help us to understand the Molecular Orbital diagrams. As an example, MO Theory allows us to predict the magnetism (paramagnetic or diamagnetic) nature of molecules, something which is difficult to do in Valence Bond theory.

For a complete list of important concepts, see the Chapter 9 Study Guide.

Resources: Read Chapter 9 in the Text

To understand the concepts behind Valence Bond Theory and Molecular Orbital Theory, you should read Chapter 9 in your textbook.

The following screencasts might prove useful to you as you study this chapter. Note that you must have Quicktime installed to watch these screencasts.

• An Introduction to Two Bonding Theories
• An Introduction to Valence Bond Theory - Boron Trifluoride
• Valence Bond Theory - Methane
• Multiple Bonds in Valence Bond Theory
• An Introduction to Molecular Orbital Theory
• Molecular Orbital Theory and Examples
• Molecular Orbital Theory and Pi Bonds
• Molecular Orbital Theory Ions and Paramagnetism

The Chapter Nine PowerPoint lecture notes which accompany this lesson will be helpful to you when going through this section. These are Web versions of the PowerPoint notes I use in my "normal" CH 222 class and should let you see what is important to me in this chapter.

A variety of handouts are available from Chapter Nine. Feel free to explore all of them or just the ones which give you difficulty.

• VSEPR Guide
• Four Principles of Molecular Orbital Theory
• MO Diagram - B₂ through N₂
• MO Diagram - O₂ through Ne₂

• Tutor: Hybridization 1
• Tutor: Hybridization 2
• Exercise: Identifying Bonding and Antibonding Orbitals
• Tutor: Homonuclear, Diatomic Molecules
• Metallic Bonding
• Simulation: Metallic Bonding: Band Theory
• Exercise: Semiconductors

These interactive exercises from W.W. Norton and Company (ChemTours) might prove useful as well:

• Hybridization
• Molecular Orbitals

Once you have mastered the concepts listed above, check out the Chapter Nine Concept Guide for a series of worked problems relating to this chapter. They will help you to ensure the mastery of the knowledge from this chapter.

Finally, test yourself (and get extra-credit in the bargain!) on the following chemistry concepts. Remember that you must have JavaScript enabled on your browser! If you get 9 out of 10 correct (or some multiple thereof), submit the information to me to receive extra credit.

1. Hybridization
2. Hybrid Orbitals

Feel free to explore and discuss the ideas from this chapter with the class.hich theory do you find most appealing? Does the complexity of MO overpower the utilitarian nature of Valence Bond theory? Take time to share your thoughts with the class on Discus regarding your impressions of these concepts and as how they relate to your life.

Please complete problem set #2 to further explore molecular bonding theories. Problem set #2 covers several questions from Chapter 9 and it can be found here . We will discuss problems like these during recitation, so come prepared to ask and answer questions.

For additional practice, try the non-assigned problems in Chapter 9. Answers to many of those problems are listed in the back of your textbook or in the Chapter Nine Student Solutions Manual.

If you need assistance on these problems, you have several options. You can visit the Learning Success Center located above the MHCC library on the Mt. Hood Community College campus; they have tutors available to help you with your chemistry homework. You can also contact me if you have any questions.