Click here for a copy of the handouts used in today's lecture

Click here for a copy of my lecture notes from today's lecture (will become an active link after the lecture).

Golden Rules for Today: 4. The most important question in organic chemistry is "Where are the electrons?"

1. More electronegative atoms attract the majority of electron density in a bond, thereby answering the most important question in chemistry.

2. Electronegativity is based upon charge attraction between protons in the nucleus (+) and elelctrons (-) so it increases with increasing nuclear charge (left to right on periodic table) but decreases with increased overall number of electrons around the nucleus (top to bottom on periodic table). Therefore, the most electronegative elements are in the top right corner of the periodic table, the least electronegative elements are on the bottom left corner.

3. Polar covalent bonds (electronegativity difference between 0.5 and 1.9) and nonpolar covalent bonds (electronegativity difference between 0 and 0.5) behave and react totally differently. Understanding where polar covalent bonds are in molecules allows you to predict chemical properties including reactivity.......this is THE KEY to learning, not memorizing chemistry!!!

4. Make sure you understand the difference between partial charges on the atoms of a polar covalent bond and formal charges on atoms in molecules that have whole charges.

5. The VSEPR model assumes areas of electron density repel each other, so areas of electron density are distributed around an atom to be as far apart as possible. Remember to count both lone pairs and bonds as areas of electron density (note that a double or triple bond counts as a single area of electron density). 4 areas of electron density = tetrahedron, 3 areas of electron density = trigonal planar, 2 areas of electron density = linear. VSEPR is usually correct, but it is wrong in a few important cases (for later) because it is NOT A THEORY, it is only a method of predicting shapes.

7. A molecular dipole moment is the vector sum of all bond dipole moments in three-dimensional space. These make great test questions since they test your understanding of geometry AND bond dipole moments.

8. Resonance contributing structures are used when more than one structure are required to describe accurately how the electrons and charges are distributed in a molecule.

9. Resonance contributing structures do not represent equilibrating structures, rather the hybrid (blending) of them is the true molecular representation. (Think of blue and red primary colors used to create a purple color, purple is not sometimes blue and sometimes red it is always just purple).

10. When drawing resonance contributing structures, draw only reasonable Lewis structures in which usually only pi bond(s) (one bond of a double or triple bond) and lone pair electrons are different.

11. When drawing resonance contributing structures, NEVER move atoms, NEVER exceed filled valence shells and NEVER create unpaired electrons when none existed before.

12. More important contributing structures will have more covalent bonds, fewer charges, and any negative charge on the more electronegative atom (and vice versa).

HOMEWORK:

Read: Sections 1.6 to 1.9in the ebook textbook. This text is part of the Longhorn Textbook access program.

Take the Daily Quiz 2 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.

Turn in the Practice Homework before 10 PM on Thursday, August 29. Click here to access the Practice Homework.This is designed to teach you how to use the Aktiv Learning electronic homework system along with Gradescope. Everyone who turns something in will get full credit. Click here to access to the Aktiv Learning electronic homework system. Click here for directions on how to use Gradescope.

Begin working on the Homework Problem Set 1, due at 10 PM on Tuesday, September 3. Click here to access the Homework Problem Set 1. 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.