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Wednesday, October 28, 2015

The One Where We All Gained Some Modeling Experience

Unit 1.B: Intramolecular Structure 

Part 2: Covalent Compounds


"What element is a girl's future best friend? Carbon."


Practice Problems:

     In this unit, the type of problem that I had the most difficulty with was when I had to apply what I knew about molecular geometry to an actual picture of a more complex compound and identify specific molecular shapes. Seeing the compound as an actual model slightly confused me since I was used to seeing compounds on paper. I understood most other practice set problems, though it did take me a while to memorize the bond angles of different molecular shapes.
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Ex. of Understood Problems
Draw the Lewis structure for the the phosphate ion, PO43-.

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Ex. of Challenging Problems
Shown below is the a molecular model for the neurotransmitter Serotonin. Circle a bent atom and place a square around a pyramidal atom.

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Activities:
     On the second day of the cycle, we were asked to predict whether methane or acetylene is more explosive. Since methane has less bonds between atoms and therefore should be "easier to separate/blow up", my group guessed that it was more explosive. We later learned that acetylene was more explosive because the triple bond between its carbon atoms has more "bond strain" and wants to break apart more than methane's single bonds. However simply learning these things just didn't do it for our class, so we got to see for ourselves just how explosive acetylene is! 

An "Irish For a Day" guest experiences methane's explosive properties firsthand

Igniting acetylene, the more explosive compound
     We were introduced to molecular geometry and learned about five different types of compound shapes. These five types were: linear, bent, triangular planar, triangular pyramidal, and tetrahedral. All these compound shapes are governed by VSEPR theory, or "valence shell electron pair repulsion".

My notes for VSEPR theory, notice the special way 3D compounds are drawn
     During this cycle we got to try and "hack" some problems taken from previous AP exams. Instead of just solving them on paper, we got to make physical models of the compounds in the problems. This gave us a unique view regarding molecular geometry problems and really helped me understand VSEPR theory more.

Two of the models we made while solving previous AP chemistry exam problems
Quiz: (To Be Edited After The Tests Get Returned)
     This cycle's second quiz required more computations in comparison to the previous one, which was one of the major factors that slowed me down. Though I prepared using both the practice set and the examples in the summary notes, the final problem (similar to the "challenging" problem mentioned above) still took me longer than I would have liked. I kept on second guessing myself and was unsure if I chose the correct central atom.

Questions:
  • Regarding the exceptions to the formula for finding a compound's number of bonds, why does hydrogen only want 2 electrons and boron only want 6?

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