10/21/13-10/25/13

This week in AP Chemistry we had the third test of the year. This exam covered the topics of covalent bonding, electron domain geometry, as well as and molecular geometry. To study for the test, I had to complete a task chain. We also went over a packet of review worksheets in class on these subjects. At home, I did the task chain multiple times and completed extra problems on the review worksheets. On Tuesday, I took the test and got an 80 percent on the multiple choice and a 98 percent on the free response. I was very satisfied with my performance on the free response but was a bit disappointed with my multiple choice test. I felt I had a fairly good grip on this subject matter (better than the material on the stoichiometry test in fact), and yet I got a score that I was not very satisfied with. Considering the fact that I have gotten relatively iffy scores on the last two multiple choice exams, I've surmised that I need to pay more attention to the multiple choice portions on tests and make a better effort to practice the types of the questions that may be found on them. All in all, I was a bit irked with my performance on the multiple choice. However, because of my results on the short answer and the fact that the multiple choice did not significantly affect my grade, I found some satisfaction in my performance on this test.

The day after the test was mole day. We were assigned an essay on the subject of polarity and hydrogen bonding as it related to an article we were given about paintball. I found the assignment to be difficult at times, as I found the prompt to be a bit vague. As only one section of the paintball article really related to polarity and hydrogen bonding, it was hard to find excerpts in the writing that supported the points in my essay. With that being said, I did learn about hydrogen bonding and how polarity relates to solubility. Hydrogen bonding is when a partially positive hydrogen atom bonded to an electronegative atom is attracted to a partially negative electronegative atom in a separate molecule. Unlike covalent bonding, there is no physical bond present, but there is attraction between the two atoms.

A hydrogen bond, represented by the dashed line.

After these two assignments, I was reintroduced to the topic of ionic bonding via a POGIL that I completed on class. Ionic bonds are bonds between a metal and a nonmetal. I learned that the size and individual charge of each ion has a profound effect on the strength of an ionic bond. The stronger the bonds in an ionic compound, the higher the melting point. For the most part, I felt I had a decent understanding of this topic. I was a bit confused about the sizes of cations and anions.

The final topic we covered this week was metals. Metals are elements that conduct heat an electricity well. They are typically malleable and ductile. They exhibit several other unique physical properties, such as luster. Metals bond together through metallic bonds. In metals, electrons called conduction bond electrons form a "sea" of electrons around atoms. These conduction bond electrons are d-orbital electrons that are promoted into the outer p-orbitals of atoms. Conduction electrons are the reason that metals conduct heat and electricity well. The more conduction electrons, the higher the melting point of the metal and the harder the metal is. Most ordinary uses of metals involve alloys. Alloys are mixtures of elements that have the properties of metals. There are two main types of alloys: substitutional alloys (solute particles take the place of solvent metal atoms) and interstitial alloys (solute particles fit in holes in between solvent metal atoms). To help learn about metals, I completed a POGIL on metals on Friday and watched a lecture on metals this weekend. I found the subject straightforward and easy to understand.