The Periodic Table
embodies the trends and properties
of all elements and is based on atomic structure and chemical bonding.
This is an image of questions 6 through 10 (all of which relate to periodic trends--see the Course EU stated above) of a pre-test I took on the first day of Chem 506: Inorganic Chemistry. In addition to answering the questions, we were asked to rate how sure/unsure we were of our answers.
This is a two part image of a portion of question 15 and all of questions 16, 19 and 25 from the first problem set for Inorganic Chemistry. These questions pertained to calculating Zeff, using Slater's rules, for establishing periodic trends.
This Inorganic Chemistry problem set was assigned and completed after we learned about Zeffective, and how calculating for Zeff can help to predict periodic trends. The questions in this portion of the problem set show that I had learned how to calculate Zeff , and was able to discuss it in relationship to "anomalies" in periodic trend, and observed behavior, vs. calculated Zeff.
While we had talked some in Organic Chemistry about shielding, we hadn't talked in depth about Zeffective, or Slater's rules. There were many questions, later in the first part of Organic Chemistry, that could be answered with "it has to do with shielding," and given a lack of a better answer, I confess to resorting to that answer, without fully understanding the implications of the statement. After Inorganic Chemistry, I better understand the periodic trends as an effect of adding electrons and shells. For instance, moving from left to right across the periodic table, the increased number of electrons in the outer shell and increased number of protons in the nucleus increases the overall attraction between those electrons and protons. This results in things like a smaller atomic radius, because there is more negative attracted to more positive. However, moving from top to bottom on the periodic table, the addition of shells means that the outermost electrons are farther away from the nucleus, and are more affected by the repulsion of the electrons in inner shells than by the attraction of the protons from the nucleus. The same effects can be seen when discussion melting point trends and boiling point trends, but instead of looking at the attraction of the electrons to its own nucleus, it is a matter of looking at the increased repulsion of the electrons in two atoms, against the attraction of the protons in their nuclei.
In terms of my baseline evidence, if I had known more about atomic structure and bonding I would have been able to answer, with confidence, that lithium has the highest melting point, because lithium, potassium, being all in the same group, have the same number of valence electrons, but lithium has the fewest amount of shells, so the the pull of the positive charge from the nucleus is less offset by the repulsion of the electrons between molecules. Since flourine, bromine, and iodine are all in the same group, if we followed the normal trend, iodine would have the the lowest boiling point, for the same reason lithium had the highest melting point in the previous instance. However, these are halogens, and due to there high electronegativity, exist as diatoms, so london dispersion forces come into play. Subsequently, iodine actually has the highest boiling point, because it has significantly more electrons to move from dipole to dipole. Nitrogen has the larger atomic radius, because boron, carbon, and nitrogen, being in the same period, have the same number of shells. Therefore, the fact that nitrogen has a higher atomic number, thus more protons and electrons, becomes important. The increase in number of charges pulling on each other causes a compacting of the atomic radius. Carbon has the highest electronegativity, because the increase in charge, moving from left to right, means that the pull of the nucleus increases. However, silicon will be less than carbon, because the effect of shielding from an addition shell. Finally, while there is some correlation between electronegativity and strength of lewis acids, it is difficult to determine lewis acid strength without also considering the corresponding lewis base. A major reason for this is that the shape of the Lewis acid as compared to the adduct created with the Lewis base determines the amount of steric interaction. For instance, the boron Lewis acids are planar molecules, whereas the adduct would be pyramidal. The phosphorus Lewis acids start as pyramidal, and would not re-hybridize, but size is still a factor. For this reason, PF3 might be predicted to be the strongest Lewis acid, but again, it is determined by whatever the corresponding Lewis base might be.
ENDURING UNDERSTANDING 2 of 3: (From Chem 505: Environmental Chemistry - Course EU)
Environmental
chemistry is a quantitative science, converting qualitative
observations and ideas into quantitative expressions.
These are images from two problem sets, and a quiz of statistics questions that I got incorrect. This class was the first exposure to statistics that I have ever had, and my initial understanding was limited, as indicated by this small sample of incorrect answers. I chose these three, in particular, because they discuss the relationship of quantitative findings to qualitative statements (see Course EU, stated above).
This is an image of a question from the first exam in Chem 505, which asks for interpretation of statistics calculations and a qualitative statement in regards to the statistical data (1b). I received full points for these questions.
This question asks for analysis of quantitative data, and a qualitative statement using the quantitative data. In particular, my use of the r and r-squared values, and the p-value is correct, and my qualitative statement, developed from the quantitative data established by the slope of the graph, was correct.
When I attempted the problem sets that were assigned before the start of the class, I spent hours, and still did not fully understand the concepts. My previous exposure to stats had been a BRIEF discussion in the first of the two education classes. After the topic was taught in Environmental Chemistry, and after I did more practice and studying, I finally understood what each statistic meant. More importantly, I was able to connect the numbers to qualitative statements that made the numbers more meaningful. In addition, I was able to take a qualitative observation, and establish how to gather quantitative data to support the qualitative observation. For instance, when we completed the Wissahickon water testing, I was able to support my qualitative observation that the water seemed unhealthy, with the quantitative data and statistical analysis that supported the qualitative observation.
ENDURING UNDERSTANDING 3 of 3: (From Chem 504: Biochemistry and Molecular Biology - Course EU)
Students
should understand how nucleic acids are key to protein synthesis.
This is an image of question #10 form the pre-test from Chem 504. It asks what the "central dogma" is, and what molecules are involved. I answered both parts of the question with a question mark. I didn't even have enough of an idea to fake an answer.
This is an image of question #2 from Quiz #1 from Chem 504. It asks almost the same question as the one posed in the pre-test, and which I had gotten incorrect. In it, I describe the process of protein formation, and role of the nucleic acids in each step (see Course EU, stated above).
This quiz was given after we learned about the role of DNA and RNA in protein synthesis. I answered the question correctly, and received full points. I discussed the three parts of protein synthesis, and explained what portions involved ribonucleic acid and which portions involved deoxyribonucleic acid, thus showing my understanding of how nucleic acids are key to protein synthesis.
I learned in MCEP that DNA and RNA, while the most common, are only two of the nucleic acids. Nucleic acids are a category of macromolecule with a backbone of alternating sugars and phosphates. What differentiates one nucleic acid from another is the attached nucleotide bases. The nucleotide bases, cytosine, uracil (in RNA), and thymine (in DNA) are called the pyramidine bases, because they contain a pyrimadine ring. The nucleotide bases adinine and guanine are called purine bases, because they contain a purine (a pyrimadine ring with an attached amidazole ring) ring. These nucleotide bases then attach to sugars, creating nucleotides, additions of phosphates create nucleosides, and then the linking of multiple monomers creates the nucleic acid chain.
DNA is a double-stranded chain, in which hydrogen bonds bond adenines to thymines, and cytosines to guanines. In its role in protein synthesis, DNA, during the replication phase, breaks into two strands so that duplicates of the partner strands are able to create hydrogen bonds to the single chains, creating new double chains. During the transcription phase of protein replication, RNA, a single-stranded chain, gathers information from the DNA, and then carries it, as a messenger (mRNA) to various parts of the cell, where the information is translated by ribosomes to form the proteins during the translation process.