Click here for a copy of my lecture notes from today's lecture

Click here for a copy of the handouts Stepwise Lewis Structure Guide

Featured Golden Rules of Chemistry: 5. Delocalization of charge over a larger area is stabilizing. , 7. Delocalization of pi electron density over a larger area is stabilizing.

1. There are three important contributing structures needed to fully describe and amide bond. The reason: Quantum Mechanics

2.The best way to think of electrons in molecules is as waves, described mathematically by three-dimensional wave function equations. Waves have quantized energy, add constructively and destrucively, and have positive and negative amplitudes. Orbitals are plotted as the square of the wave function.

3. The electron density in molecules can be described mathematically by adding the wave functions of all the atomic orbitals for all the atoms in the entire molecule, an approach refered to as molecular orbital theory. This is the way we want you to think about pi bonds, but it is not useful for students trying to understand sigma bonding in molecules.

4. The wave functions for the valence atomic orbitals on each atom can be added together (hybridized) first, before looking for overlap with orbitals from other atoms. This is called valence bond theory and is the best way for students to think about sigma bonding in molecules as first described by Linus Pauling.

A. When the 2s orbital is hybridized with all three 2p orbitals, you get sp3 hybridization that has major lobes pointed in a tetrahedral geometry. Sp3 hybridized atoms take part in only single (sigma) bonds.

B. For sp2 hybridization, the 2s and only two of the 2p orbitals combine to make three major lobes in a trigonal planar geometry. The third 2p orbital, orthogonal to the three sp2 orbitals, does not take part in hybridization. It is available to take part in pi bonding as a regular 2p orbital. Sp2 atoms usually take part in double bonds.

C. For sp hybridization, the 2s and only one of the 2p orbitals combine (hybridize) to make two major lobes in a linear geometry. The other two 2p orbitals, which are orthogonal to each other and the 2 sp lobes, are available to take part in making pi bonds with other 2p orbitals, usually resulting in a triple bond.

5. You need to be able to think about all sigma bonding in molecules as being derived from the overlap of hybridized orbitals and/or H1s orbitals and all pi bonding as being derived from overlap of unhybridized 2p orbitals.

6. Watch this video to make sure you understand what we want!

7. Although it might not be obvious, molecular orbital theory and valence bond theory make very similar overall predictions concerning the elcctron density in the sigma bonds of molecules. When all the molecular orbitals are summed, they predict electron density existing primarily shared between the atoms (bonding) just like the valence bond overlap model does. Valence bond theory just makes more sense to humans.

HOMEWORK:

Read: Sections 1.10 to 2.2 in the ebook textbook. This text is part of the Longhorn Textbook access program.

Take the Daily Quiz 3 before 10 PM tomorrow. Click here to access the quiz. These quizzes are designed to review the important material from today's lecture. Together, they will count as 3% of your final grade.

Begin working on the Homework Problem Set 2, due at 10 PM on Tuesday, September 10. Click here to access the Homework Problem Set 2. Note there are Aktiv Learning and Gradescope Questions, and you MUST DO BOTH. Collectively, homeworks count for 10% of your final course grade. The Aktiv Learning homework provides multiple attempts and provides feedback. It is intended to help you prepare for the Gradescope Questions, so we recommend you do the Aktiv Learning questions first.

These quizzes and homeworks are designed to keep you up to date with the course material and prepare you for the format of the exams. Taken together, your cumulative daily quiz and homework score will count for 13% of your final grade.