10/14/13-10/18/13

This past week in AP Chemistry was the most confusing so far. I was introduced to the concept of hybridization and sigma and pi bonds.

In covalent bonds, electrons can only be shared if the electron orbitals of two atoms overlap. Hybridization occurs when these orbitals combine to form new, hybrid orbitals. For example, the s and p orbitals combine to form an sp orbital. There are three widely accepted forms of hybridization: sp, sp², and sp³. Hybridization is a theory; whether or not it works beyond the second period is questioned. Additionally, hybridization is central to valence bond theory, a.k.a. sigma and pi bonding, which is explained later. 

sp hybridization.

I did not understand the concept hybridization well, which would explain my rather lackluster explanation. I do know that you can determine the hybridization of a molecule by simply counting the number of electron domains around the central atom. If there are two electron domains, the hybridization is sp. If there are three electron domains around the central atom, the hybridization is sp². If there are four electron domains, the hybridization is sp³. Whether hybridization occurs beyond that is hotly contested within the scientific world and does not concern me. However, conceptually I do not understand hybridization beyond the notion that orbitals can combine to make "hybrid" orbitals. To cover these concepts, I watched a lecture on hybridization and completed the Hybrid Orbitals POGIL for homework. While what I know may be enough to get by on the test, I still would like to understand the concept of hybridization more.


I found the concept of sigma and pi bonds to be more straightforward. Sigma bonds are bonds with head to head overlap and cylindrical symmetry of electron density about the internuclear axis. Pi bonds are bonds with side to side overlap. Electron density is above or below the internuclear axis. In a single bond there is one sigma bond. In a double bond there is one sigma bond and one pi bond. In a triple bond there is one sigma bond and two pi bonds. I was confused about this concept until I completed the task chain quiz that involved sigma and pi bonds. When I got an answer wrong regarding a sigma and pi bond, the information window that popped up gave a good explanation of sigma and pi bonds. To cover sigma and pi bonds, I watched a lecture on the subject. This website also gave me some clarity on the subject.

There is a pi bond between the blue p orbitals, as there is side to side overlap between them. There is a sigma bond between the green orbitals, as there is head to head overlap between them. 

Throughout the week in class I worked on a lab/activity involving the program Web MO in which I modeled molecules from the VSEPR Theory lab with my table group. Using the program, I determined the bond angles, polarity, dipole moment, and more for several molecules. The activity really helped me better understand the concepts of bond and molecular polarity, as well as how unbonded electron pairs affect the shape of molecules.