I’m writing all the way from California, where I returned to for Spring Break. Luckily, I escaped just in time to dodge the storm earlier this week in Princeton. Here are some of the things I came back to (and missed greatly).
Over the past few days I’ve had some time to step away from the craziness that was midterms week—good thing I’m writing this post towards the end of break to somewhat ease me back into the academic routine again. That being said, here’s a bit about one of the more interesting midterms I had to take: CHM 215.
For some background information, CHM 215 is a general chemistry course that essentially combines topics from CHM 201 and CHM 202 into one semester. What I especially like about the course is that the class size is quite small—around 20 students in total—which is pretty amazing given that it covers general chemistry. For the first half of the semester, we focused on topics such as quantum mechanics, atomic theory and bonding, molecular orbital theory, and the VSEPR (valence shell electron pair repulsion) model.
The Midterm Exam
The exam itself was designed to be taken in two hours, outside of the usual class time (which is scheduled by the registrar); I took mine in a lecture hall from 7:30 PM – 9:30 PM. Because it was held at night, it was important that I had enough energy to stay focused. Also, although two hours for an exam seems like a long time, it vanishes very quickly. One moment you begin, and before you know it time is already up. Thus, it is vital to pace yourself!
About a week before the exam, my professor told us the format and the specific topics to focus on. He specified that the entire exam was free response (my enemy) and that we should study the Bohr Model, Atomic Orbitals and Linear Combinations of Atomic Orbitals, Periodic Trends, Molecular Orbital Diagrams, Lewis Structures and VSEPR, and Symmetry Point Groups. This was especially helpful because we knew exactly what to expect of the exam. That is not to say that it wasn’t tough, though!!
One of the concepts that I struggled with in particular in preparation for the exam was drawing Molecular Orbital Diagrams. Given that I had only first learned of MO Theory through this course, it was a bit of a challenge to grasp.
In class we started MO Theory by looking at diatomic molecules (like HF or O2), where we would use the valence electrons and their respective orbitals in each atom to see how they would constructively and destructively interact. This allows us to determine whether each interaction is sigma or pi, and whether each is bonding or antibonding. From completing the diagram we can determine the bond order and other properties, such as whether the molecule is paramagnetic or diamagnetic.
This became even more confusing once we started drawing MO diagrams for polyatomic molecules like H2O. Here, what really tripped me up was figuring out all of the various combinations between the atomic orbitals, their respective energies, and the nonbonding orbitals if there were any.
Nonetheless, I really find the material we are learning to be quite interesting. Even if it is a bit confusing at times, it’s a good feeling when you finally understand it. Midterms week was certainly tough, but it’ll all be okay!
Now it’s time to go back to getting through the rest of the semester! Until next time!