9/30/13 Weekly Reflection

This week, we started chemical bonding and wrapped up Stoichiometry. We also had a test partway through the week on no-calculator math and stoichiometry, including limiting reactant problems, problems on calculating percent yield, and some about mole ratios and determining how much of a compound would be produced in a given reaction. After the test, we started with a POGIL on Lewis dot structures, which are simple representations of an atom with the element symbol in the center and the valence electrons represented as dots spaced appropriately around the element symbol. They are also very useful for looking at compounds and showing bonds. On Friday, we did some more, slightly more complicated Lewis structures, including those without a balanced charge. The Lewis structures were a good segue into the weekend homework, which was about bonding, specifically ionic and covalent bonding. It goes into detail about how they work, the differences between them, and how Lewis dot structures can be helpful when diagramming them.

I only had a few questions about what we learned this week, which is understandable considering that we only spent the last two days learning new material. In covalent bonds, how does the electron sharing work? How does the electron orbit both nuclei simultaneously? I did my best to participate a lot this week, although it took some time to adjust to having new table groups. I don't really like POGILs, although I understand the ideology behind them.I like the activity, I just don't like how rigid the jobs and their definitions are. It seems that some of the jobs, such as reader, are essentially useless (after all, we can all read.) The rest of the jobs are usually divided based on skill sets, or who is better at what, but I understand that POGILs are supposed to foster those skill sets in everyone. I think that I understood the material well. We didn't really get into complicated Lewis Dot structures - we mostly did basics, and because of the nature of bonding and how abstract it is, we are taking a decent amount of time on it. I definitely need to work on understanding bonds in a more solidly conceptual sense, as opposed to just vaguely having a sense of what is going on.  I've also been wondering what the best way to visualize a molecule is. Is it better to envision the electrons as a cloud or as individual electrons orbiting the nucleus? If they are orbiting, should the electrons be orbiting like Saturn's rings or Jupiter's moons? I will probably be working on that for a while.

9/23/13 Weekly Reflection

This week, we focused on stoichiometry, going more in depth and expanding it to more practical uses. We dealt with limiting and excess reactants and also examined empirical formulas and how to convert them to molecular formulas given the necessary mass percents and formula weights. We also looked at yield in the form of theoretical, actual and percent yield problems.The limiting reactant is the reactant that is completely consumed in the reaction - the one that limits the number of times the reaction can occur. The excess reactant is the reactant that is not completely consumed in the reaction - the one that is in excess, that is left over after the reaction is complete. Empirical formulas are formulas that express the number of atoms in relation to one another, with no regard paid to absolute quantities or structures of compounds. Molecular formulas are formulas that represent the number of atoms in a compound. Limiting and excess reactants are very important in stoichiometry, especially when one is actually conducting an experiment given only the quantities of reactant and the chemical reaction. Empirical formulas have thus far only been really important when converting mass percents to molecular formulas, but I'm sure they will have other uses further down the road. In an effort to hone our knowledge of stoichiometry and calculations involving stoichiometry and empirical formulas, we did a series of worksheets and discussed them in class. I found a website that covers this information as well. We also did a couple of other sets of worksheets and then presented our work (both successes and failures) to the class for discussion and analysis.

While I understand most of what was discussed during this week, seeing as most of stoichiometry is just simple calculations, I have been getting really strange answers for the more difficult problems that convert mass percents to molecular formulas. I think most of my problem is with rounding - more when to round and how far, given that we often have to round two or three decimal places off to get the whole numbers we wanted. I found this power point extremely helpful, though. I loved how 'common sense' this section was. It followed a natural progression from masses and mass percents to moles of a substance, then using moles to find an overall ratio, and on to the molecular formula. I tried hard to participate a lot in class this week, especially with presenting the information, even though I'm not good at it. I can only get better from here. I understood this section really well, which does not suprise me, considering the simplicity of this section. I have a few questions that may extend this, although I'm not sure how well they will do so. What is a structural formula and what does it tell you about the structure of a molecule? What other uses are there for an empirical formula?Other slightly less related questions: What determines whether or not two substances will react? Are the materials such as glass used in test tubes potentially dangerous if a chemical reaction is accidentally induced? Can the results to a chemical reaction that hasn't been done before be predicted and if so, how?  I will be puzzling over these and the relationships between various different molecules, especially relationships in hundreds of unknown chemical reactions, for a while.

9/16/13 Weekly Reflection

This week, our main focus was on stoichiometry, which deals with the relative quantities of reactants and products in chemical reactions, the format of labs and lab reports, absorbance and transmission of light, and concentration of substances. They were all linked by the common thread of our first ever lab in AP Chem, the Blue #1 Concentration lab. In this lab we learned how to use a colorimeter and our lab notebooks, and did fairly simple calculations and took similarly simple measurements in an effort to learn more about concentration and how it affects the transmission of light. We concluded that, as the concentration of Blue #1 dye increases, the amount of light absorbed also increases and the amount of light transmitted decreases. The relationships between some of the main ideas were put into formula that we looked at as well in an effort to get to know the subjects we were studying even better. Also, we did worksheets and moodle quizzes to further cement our knowledge on the subjects, along with informative in-class discussions during which we had the opportunity to struggle and win the knowledge we were trying to acquire. I still have some questions about what we learned. Some of them are more extensions on what we learned, while others are more of a vague curiosity or confusion about topics surrounding the experiment, while still others are specific points that I'm confused about in the lab. For example, what property of distilled water gives it a color and how does it respond to different wavelengths? How is k found in A=kC, excluding when it is possible to just solve for it? I felt a bit over my head this week, although after completing the lab questions I understand everything we covered much better. Given that, I thought my participation level was certainly appropriate, and I did my best to learn from the people around me. I also did my best to share any sudden realizations I had and help my group to understand everything better. My understanding of the subject matter is fairly good, but although I understand the theory and ideas presented I have yet to gain any intuitive sense about the material we studied this week. Mostly I need to work on balancing chemical equations and more complicated conversion problems, like the questions we answered in class that were later part of the lab report. I had no idea how to figure them out and was frustrated by that as well as the fact that I had to rely on other people who got it faster and easier than I did. I understood how it worked after the fact, it was just getting there that I had trouble with. I have a lot to think about in terms of stoichiometry and concentration, especially in everyday situations.