10-7-13

This week we started learning more and more about Lewis structures and molecules. We started with bond order and bond strength. Bond energy is defined as the energy required to sever the bond that holds two adjacent atoms together in a molecule. It's usually expressed on a molar basis. Bond order tells the type of bond between two atoms. For example, two atoms with a single bond has a bond order of 1. Two atoms with a triple bond have a bond order of 3. The higher the atomic number, the higher the bond order. Triple bonds have the highest amount of strength, while single bonds have the lowest amount of strength. Bond length is defined as the distance between the nuclei of two bonding atoms. The shorter the bond, the stronger the bond because there is more energy the shorter the bond.

We also did a lab to try and determine the percentage by mass (mass percent) of copper in brass screws or any other brass item. It was important during the lab to use extreme safety because of the concentrated nitric acid. Concentrated nitric acid is corrosive and will attack and destroy metals, plastics, and proteins. Skin contact with the acid would discolor the skin for days. The gas that forms from it is a toxic, reddish-brown gas of NO2. The nitric acid addition was performed under the fume hood and we all made sure we wore goggles. The nitric acid was added to the brass screw and left in the beaker over night. The next day, after the screw had dissolved, our group used the visual comparison test to determine the concentration of the unknown solution. The two test tubes of the reaction solution, and the unknown solution were placed on top of a white sheet of paper and then the intensity of the color of each solution was compared and the solution was removed or added until the colors finally matched. Then, after measuring the depth of each solution we used the equation (Molarity1)(Depth1) = (Molarity2)(Depth2). 

On Friday, we started the VSEPR Theory Lab and 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. This week, I'd give my understanding on this subject about an 8. I really understand the relationship between bond order, bond length, and bond energy. I really enjoyed the lab with watching the brass dissolve, and the colored gas come from the reaction between the two elements. The VSPER lab (that's still not done) was also really fun with the balloons, although I probably got a little carried away with the balloons. I still have questions on how to name the shapes that came from the gum drop models? I don't quite understand the octahedral and square pyramid part, so I'm hoping this week I'll get a better understanding of it.