10-14-13

This week, we started out by finishing up the VSEPR structures, then more Lewis structures, and Formal charges. We use formal charges to make correct Lewis structures which can then be used to identify VSEPR structures.
We started out finishing up the VSEPR theory lab. We used balloons to determine the shape and angles of molecules. Electron domains are a region where electrons are most likely to be found. Our group used balloons to make SF6 and BrF5. There are two types of of VSEPR structures. One is Electron Domain geometry which is based off how many electron domains there are per central atom. We learned that the 5 possible shapes that can be formed by electron domains: Linear, Trigonal Planar, Tetrahedral, Trigonal Pyramidal, and Octahedral. Linear structures contain two electron domains, trigonal planar have three electron domains, tetrahedral have four electron domains, trigonal bipyramidal have five electron domains and octahedral have six electron domains. The second type of structure is molecular domain geometry. Molecular domain geometry structures are based on how many actual bonded atoms there are connected to the central atom. If all of the electron domains of a central atom are bonded to another atom, then the molecular domain geometries are exactly the same as the electron domain geometries. 

We used balloons to create models of electron domain geometries and used gummies to create molecular geometries. These structures made out of the different items made it a lot easier to visualize the shape of the molecular structure, but I feel like the balloons were a little easier to use because the gummies kept melting out of place. 

We also learned a lot about how to make Lewis structures by using formal charges. Formal charges are assigned to atoms in molecules according to a set of rules. 1. Nonbonding electrons are assigned to the attached atom. 2. Shared electrons are evenly divided between the bonded atoms. A Lewis structure is not complete unless the formal charges are indicated (except "0" is not used). Formal charges by doing formal charge = core charge - number of assigned electrons. The best Lewis structures are the ones with the lowest formal charges. Formal charges greater than positive or negative 1 are never found in good Lewis structures. We also learned that atoms in the 3rd, 4th, and 5th periods can have extended octets, meaning that the sum of the bonding and lone-pair electrons can be greater than 8. 

This week I'd give my understanding on this subject about a 7. I really understand the idea of formal charges, and how to find them. It was easy for me to explain to my classmates on how to find it and how to use it. I also understand the extended octets on the 3rd, 4th, and 5th periods, and helped to remind my tablemates that when we were whiteboarding some of the atoms could have more than eight atoms. The reason my understanding of the topics is at a higher rating this week is because of the molecular and electron domain geometries. I'm still unsure about how to identify the different shapes of each molecule. My questions for this week would be how to identify the angles in the electron and molecular domain geometries? I hope this week I can understand electron domain and molecular geometries.