9/23/13-9/27/13

This week in AP Chemistry I took the second exam of the school year. The test covered stoichiometry, which I have been learning since the beginning of the year, and was held on Wednesday. To prepare for the test, we reviewed many of the concepts of stoichiometry in class using socrative.com. Additionally, to prepare for the test I watched a lecture on no-calculator math and completed three no-calculator math hotpots. I used the hot potato quizzes to study, doing each quiz two times. After starting to do the hotpots I became worried about the exam. I was able to complete the hotpots with most of the correct answers, but it was taking me too much time. Upon looking at a problem, it would take me a while to delineate what calculations to use to find the solution. However, I resolved this problem by simply practicing the quizzes again and by figuring out the shortest way to achieve the correct solution. I felt comfortable with the majority of the concepts of stoichiometry, so I primarily studied using the no-calculator math quizzes. On the test I got a B on the multiple choice portion. I have not seen the corrected copy of my test, however, I assume that I lost points on the questions where I had to chose an appropriate diagram of a given reaction. These were the problems on the hot potato quizzes that I had the most trouble with. On the free response I got a perfect score. Despite the fact that I got an 86 on the multiple choice, overall, I was satisfied with my performance on the stoichiometry exam. I was anticipating getting a far worse score prior to taking the exam. Nevertheless, I still would like to come in after school to see what problems I got incorrect.

After the test on Wednesday, we moved on to learning about Lewis dot diagrams. Lewis dot diagrams are renderings of substances that also show the number of valence electrons per atom and covalent bonds in the substance. To make one of the diagrams, you first write the element symbols. Then, you draw dots around the elements where there are valence electrons and dashes where there are covalent bonds. The total number of valence electrons in the substance should be accurately represented in the diagram. The diagrams should also follow the octet rule (atoms tend to have eight electrons in their outer shell). Sometimes, Lewis dot diagrams do not include the dots that represent valence electrons. However, for AP Chemistry it is always necessary to include dots in the diagrams.

Examples of Lewis Dot Diagrams. Valence electrons are represented by dots, while covalent bonds are represented by dashes.

To help learn about the Lewis dot diagrams, I completed a POGIL in class with my group and watched two lectures on the diagrams at home this weekend. I also found this website which offers a good summary on how to properly draw the diagrams. At first, I was unclear as to how to determine how many bonds to place in the Lewis dot structure, but the lecture helped to clear this up for me. Other than that, I believe I understood the Lewis dot diagrams well.