Week 7 Blog Entry

This week in AP Chemistry, we started off the week by going over some more review problems in preparation for our covalent bonding unit test. The night before, we were to complete a task chain which helped us review for our test. When I answered a question wrong—which happened quite often—there was valuable feedback which I added to my notes. On Tuesday, we took our test and I was actually quite happy with my results, although my most prominent emotion was relief.

Wednesday was perhaps the most important day of all, however—it was Mole Day! Mole Day (10/23) was a great time to relax in AP Chem and enjoy some mole cookies and hot chocolate. We had to crawl into class through the mole cave, a not-so-easy task with an unreasonably heavy backpack to carry. We listened to a mole day song, a tune that ended up getting stuck in my head for the rest of the day. We also received an essay assignment discussing the chemistry of paintballs. Truthfully, I have always wanted to go paintballing but I’m hesitant due to the pain of an exploding paintball on skin. The article discussed some familiar concepts such as polarity and hydrogen bonding, and also introduced some new ones such as solubility.

On Thursday, we took a grueling AP Chem pretest and filled in the multiple-choice answer we thought was best. I flipped through the packet of test questions and answered the ones I knew first—these usually involved VSEPR and stoichiometry. However, I would say that 90% of the test contained questions of which I had no idea how to answer. It gave me a good idea on what the AP Chem test at the end of the year will be like. Truthfully, I ended up guessing on most of the answers but I was pleasantly surprised when found out I scored around 40% (I was expecting something in the 10-20% range)! That just goes to show that my blind guessing skills can’t be all bad.

On Friday, our class began our new unit on metals and ionic bonding. We completed a POGIL on ionic bonding and started a new metals POGIL. We explored the relationship between ion size and melting point, and determined the most common ion of an element. Metals were usually cations, and nonmetals were anions. Dr. J displayed how the melting point increased along with the energy by using a sodium model with magnets. It took force to pull the atoms apart, and there was energy when the atoms snapped back together.

This weekend, we also completed a lecture quiz on metals. The lecture involved taking an excerpt from a movie that went into depth on the process of making an alloy for a bell. The video was actually very interesting to me because at one point, a sample of brass was analyzed in a machine and superimposed on a computer. The actual atoms could be seen! That was really neat for me; it makes me wonder if eventually, we’ll be able to capture the exact shape of an atom so we won’t need to rely completely on VSEPR theory.

Week 6 Blog Entry

This week in AP Chem, we began compiling a table of the thirteen different molecules we used back in our first VSEPR POGIL. We used software called WebMO. This is a neat computer program that lets you create any molecule and then submit it as a job, where it can then be optimized for different forms. For example, we used the geometry and molecular orbital optimization. From this software we could record the bond angles of the molecule, find and display the dipole moment, and also create electrostatic potential models that showed the polarity of the molecule. We then took all of this information and compiled it in a table, which we then used to create a full lab report on each of the 13 molecules.

I was kind of confused at first when making the molecules; I had to scrutinize the instructional packet in order to reassure myself that I was performing the steps correctly. However, after two or three molecules, I had gotten the hang of creating new molecules and soon enough, I whipped out nearly ten molecules by myself (molecular and geometry optimization) within the first period! It became quite methodical for me, and I was really impressed by the growing ease with which I could identify the molecular shapes. I remember looking at the molecular optimization of BF₃ and unconsciously identifying it as a trigonal planar molecule. I was quite surprised how fast I arrived to that conclusion, when just a week earlier I was struggling with the VSEPR balloon molecules and scratching my head over how to determine the shape and bond angles. The WebMO models really helped me gain a lot of practice on determine VSEPR shape.

On day two of model making, we optimized the electrostatic potential models for each molecule. This was incredibly helpful for clarifying the concept of polarity for me. When completing the polarity lecture quiz, I really couldn’t wrap my head around the concept of how electrons would be more dense in certain parts of the molecule. The electrostatic maps showed the electron density through the use of color, where the more red areas would represent more electrons and the blue areas would signify fewer electrons. In every case, the more electronegative atoms in the molecule were surrounded by red. This is because these atoms attract more electrons, resulting in a more electron-dense area.

I could also see why some molecules were overall nonpolar even if they had polar bonds. I could visualize the surrounding atoms as horses pulling outwards from the central atom. If they were symmetrically spaced from each other about the central atom and pulled with the same strength (magnitude), then they would all cancel out and result in a net dipole moment of 0.

At the end of the week, we did some reviewing of our upcoming test. We discussed polarity and whiteboarded some questions from Lectures 9 & 10. As usual, the whiteboarding really helped me gain some extra tips on how to go about solving a chemistry problem. Each of my classmates has a different way of approaching a problem, and that became visible when each group demonstrated their answer for the whiteboard questions. Whenever a group did not correctly answer a question, it was very helpful when Dr. Finnan went through the reason why it was incorrect because I would often make the same mistake the group did.

Overall, I feel much more confident in my knowledge of Lewis structures and VSEPR models. I have become stronger in polarity, but I still have some reviewing to do to feel completely sure of myself. I also have some touching up to do on concepts like sigma and pi bonding, and bond orders/lengths.

Week 5 Blog Entry

This week in AP Chem, we focused in on VSEPR models and how they can tell us about the shape of a molecule. We first created balloon models of given molecules, as they give a pretty good representation on how a molecule will be shaped. In our table groups, we drew the Lewis structure for our molecule and then counted the bonding atoms and the lone pairs, which also gave us our molecular class. After we used this information to create our balloon models, we observed how the shape the balloons formed with each other made a certain shape for the electron domain geometry (tetrahedral, trigonal bipyramidal, etc.).

We also made gumdrop models of the same molecule, but this time created the molecular domain geometry instead of the electron domain geometry. If there were any lone pairs about the central atom, then the molecular and electron domain geometries would differ.

We briefly discussed the percent copper in brass solution lab we performed last week and created a graph with the absorbances of our solution. We used this graph to calculate our mass percent of copper.

We also completed a lecture quiz on Polarity and reviewed Lewis structures near the end of the week. We completed a POGIL on hypervalency, and noticed which atoms could be hypervalent (atoms in period three and above.).

I am beginning to notice my improvement and efficiency in drawing the Lewis structures for many different molecules, although some of the more challenging molecules still manage to get the better of me. Admittedly, I am still kind of shaky with the entire resonance structure and bond order concept, although I am beginning to see the correlation between the two concepts. I feel like I also need some more practice in VSEPR models. I haven’t fully memorized the electron and molecular domain geometries yet, but I now understand why certain angles in the electron domain are formed.

When we created balloon models, we represented the bonded atoms as red balloons and the unbounded electrons as white balloons. Because these white balloons were slightly bigger than the bonded atoms, they wanted to push down on the bonded atoms in order to decrease the repulsion between the electrons.  This helped me understand the concept of the VSPER theory—how atoms want to arrange themselves in the best way to minimize repulsion.

Overall, I think I have dealt with a great deal of new material this week. I have become more confident in drawing Lewis structures, even though I still feel I have a long way to go until I become completely adept in drawing them perfectly. I still have trouble with drawing resonance structures and making sure I have compensated for every electron that belongs in that molecule. I also have some room for improvement in VSEPR models, mostly in memorizing the angles that form from the central atom and exactly what shape they create. Hybridization and polarity were also somewhat challenging concepts for me, which means that I’ll devote extra attention to them to ensure that I understand them fully.

Week 4 Blog Entry

This week in AP Chem, we went a little more in depth with Lewis structures, and completed a few lecture quizzes. We began the week with a POGIL on bond order and length and also did a few lecture quizzes to get some practice. However, the bulk of our week was spent discussing and performing our second lab.

We started off with an intro to the lab, in which we were trying to find out how much copper there is in a brass screw. We were given the reaction of copper and nitric acid, and spent an entire class period plowing through it to try and find the minimum amount of nitric acid we could use in the reaction. It involved some brushing up on stoichiometry, but as a class, we whiteboarded our process and all of us were able to understand the process fairly easily by then. It still catches me by surprise how much I have improved in stoichiometry when it used to be a grueling process for me just three weeks earlier. 

The next day, we came up with some beginning questions and began our experiment; we were trying to determine the relationship of the mass percent of copper in the Cu(NO3)2 and also the absorbance. We also tested two types of screws—a light screw and a slightly darker, heavier screw.

During the first day, we only had time to actually perform the reaction with our screw and the nitric acid. It was actually a really cool experience for me; after all, it was the first true reaction I witnessed in chemistry! I was just expecting some normal color change (like the many universal indicators I had used in the health and medicine magnet), but what happened was much more exciting. The nitric acid, which was a clear solution, was poured into our beaker containing the screw. Right away, the solution started bubbling and giving off a brown gas, which was toxic (all colored gases are considered toxic). As the screw was being dissolved, the solution began turning into a clear blue. The reaction went on for quite a while, and I could still see the remnants of some of the brown gas as I left class that day.

The day after, we tested the absorbance of our solution by diluting it with deionized water and testing it in the colorimeter. By the end of the class period I had gotten quite adept at the practice of using the bulb attached to a volumetric pipette to draw out solutions. We recorded our absorbance values on the board and in our lab journal.

At the end of the week, we finished off by introducing VSEPR models through the use of balloons which modeled our molecules.

It amazes me how quickly we are moving in AP chemistry, yet I don’t feel like I’m falling behind. Obviously, it is an extremely challenging class and I face difficult problems everyday, but I’m actually enjoying it. I am finding myself looking at the ingredients of my shampoo, or thinking about the compounds in my food, and I find myself thinking about where the energy of my food comes from (now I know it comes from breaking chemical bonds) and recognizing some compound names in places I would never suspect to find them. It is a truly engaging process for me. Truthfully, when I started the course, I didn’t really think I would enjoy chemistry. But I am learning new things everyday, and realizing how truly fascinating the world of chemistry is. It may sound cliché, but chemistry really is teaching me more about the world around me and how to interact with it. It can be stressful, but I feel like in the long run, chemistry will prove very rewarding for me.