Friday March 4th, 2011

Today, Mr. H began class by having everyone open their packets to page 26. Once there, he stressed the importance of including for question 17: AX5, AX6, AX2E3, AX4E2. Its important to know that all of these molecules are NONPOLAR. Additionally, he broke down the AXiEj molecule and explained what each variable represented:




A<---------- Central Atom


X<------------------- Terminal atoms


i<--------------------# of terminal atoms


E<-------------------- Non-bonded electron pairs


j<----------------------- # of non-bonded electron pairs


Next, Mr. H went to Grace's blog and emphasized the important parts of the blog. He also stressed the idea about dipoles, especially when grace says "The greater the number in the electro- negativity, the more electrons an element pulls. Cl, has a high number than H, resulting in more electrons towards itself. It is greedy. These are called dipoles. " It is essential to understand the idea behind dipoles, because by understanding dipoles, you are able to understand the molecular geometry of different kinds of molecules. After going over Grace's blog, Mr. H had the class open their packets to page 9 where he continued to talk about the "AXiEj" molecule and explain how to figure out degree angles and types of molecular geometry. For instance, lets take SO2. Here is what it looks like based on the lewis dot structure and its molecular geomtery:

Lewis Dot Structure

Molecular Geometry (Bent)

Based on the Lewis Dot structure, SO2 has 3 total pairs. I was able to figure out the total pairs by focusing around the central atom, which is S, and any bonds or unpaired electrons. So, since we know that the total pairs in SO2 is 3, this limits our answers to either trigonal planar or bent. Next, you count the total number of bonding pairs. Although SO2 has 1 double bond and 1 single bond, the total number of bonding pairs in SO2 is 2 bonding pairs. An important thing to know when counting bonding pairs is that no matter if a bond is a sing, double, or triple bond, it still only counts as 1 bonding pair. So, using that information, you can conclude that SO2 has 2 bonding pairs. Next, you have to count the number of lone pairs. Once again, you focus around the central atom. Since (S) only has 1 pair of electrons surrounding it, that means that it has 1 lone pair. So in the end, the number of electron pairs comes out to be 3-2-1. Once again, this stands for 3 total pairs, 2 bonding pairs, and 1 lone pair. If you are confused on how to find the total number of pairs, a trick that you can use is that if you add the number of bonding pairs by the number of lone pairs, you'll get the number of total pairs. So now since you know the number of electron pairs, you turn to page 9 of your packet and look for the bonding pairs that coincide with what you found. You can find the answer to this problem in the third row of the diagram. when you look across, you can see that the molecular geometry of SO2 is bent. (the picture above this paragraph shows the molecular geometry of SO2). Now, to find out the "AXiEj" molecular set up of SO2, you use the information that i provided at the beginning of this blog and apply it to the molecule SO2. Since "S" was the Central atom, you substitute "S" for A. So far, it looks like this: SXiEj. Next, you substitute "O" for X, because "O" is the terminal atom in this molecule. So now, you have SOiEj. Considering that you had 2 Oxygen atoms, you replace "i" with 2. So now you should have SO2Ej. Next, considering the fact that SO2 had 1 lone pair, you would end up replacing "j" with 1. At the end, you can now see that the molecule was SO2, and it had 1 lone pair electron. Considering the fact that now we know the molecular geometry of SO2,  the next thing to find is the degree angle. If you look at the picture above this paragraph or the picture on page 9, you can see how the bent molecule forms an angle that is bigger than 90 degrees. Now, you have a few answers to choose from. The possible degree angles are: 180, 120, and 109.5. First of all, we can eliminate one of the answers right away, because the picture above doesn't form a straight line, therefore we can eliminate 180 degrees. Next, based on the picture, you would have to conclude that the its 120 degrees because its bigger than 90 degrees, but also less than 180. The choice for 109.5 would be eliminated because the angle formed is not very narrow, instead its much wider. By using all the information i have provided, anyone can find out a molecules molecular geometry and angle measurement.

The next thing we did after going over page 9, was a lab. The lab we did was CB1-Molecular Geometry and Polarity Lab. Purpose: To determine the Lewis structure AXiEj notation, molecular geometry and polarity of the following molecules: CH4, NH3, OH2, CO2, SO2, XeF2, SF4. Mr. H color-coded each element with a certain piece in a box of pieces which would be used to create models of molecules. In this lab, you and another partner built models of each molecule, recorded the necessary data, found the molecular geometry, found AXiEj, but didn't find its polarity. (that is to be completed later on). After spending about 10 minutes on this lab, Mr. H passed out a quiz to the entire class and we took a quiz for the last 20 minutes.

Tonights homework: Webassign 7.4 Rdg Sheet. Due: Tuesday March 8