Updated August 28th, 2021 For those of you who have already had me, you know that this is the page to come to to get assignments, labs, weekly announcements and summaries. Past weeks announcements will be placed in the Quarter 1 Archives drop-down menu.
Do make sure you have printed out both the O-Chem Syllabus and Weekly Pacing Guide.
This week we addressed the uniqueness of carbon as that perfect atom for building because it can form bonds with one, two, three, or four other atoms lending itself to a wide array of molecular geometries.
Another great feature about C-C bonds is the fact they are VERY strong, with a single C-C bond being almost three times as strong as a single Si-Si bond. This is because C-C bonds are much shorter because the atomic radii of C are smaller.
In addition to learning about the uniqueness of carbon, we reviewed other concepts from your General Chemistry class. I hope you clearly understand at this point just how important outer (valence) electrons are in chemical reactions. We will spend quite a bit of time this week examining the nature of these outer electrons as we work through formal charge and resonance theory. For homework, if you have not already done so, watch the videos up to Section 1.9 (Video/ Resources drop down menus); do not stress if you do not understand everything you are watching, as we will spend time during class to clarify these subjects!
Recollect from Thursday's class we mentioned the idea that molecules are "reactive" when we note a separation of charges within them - this separation is usually due to the positions and movements of their electrons. Note the electrostatic potential maps for four molecules below:
The first molecule, hydrofluoric acid (HF) shows electron density near the left side of the molecule, where the fluorine atom is. Since fluorine is the THE most electronegative atom it is going to strongly pull electrons towards itself, making the molecule very polar.
As a consequence, a positively charged ion, such as Na+ would be attracted to the pole where the fluorine atom is (the red side), and a negatively charged ion, such as OH- would be attracted to the pole where the hydrogen atom is (the blue side). Notice that the polar nature of the HF molecule is further symbolized by the partial positive and partial negative signs.
In looking at these maps, which of the four molecules would be most soluble in an organic, nonpolar solvent, such as benzene? Recollect from General Chemistry that "like dissolves like." Which of these molecules do you think is the most nonpolar?
On Thursday, I asked you all to go ahead and complete the assignment for Drawing Lewis Structures on you own at home. Do make sure you bring this on Tuesday if you have any problems finishing it! I am more than happy to discuss this with you during class.
The big overarching question we have to ask ourselves in the world of organic chemistry is, "What drives organic reactions?" It is my hope by the end of this course that you understand the few principles that drive reactions between organic molecules - the overarching one being thermodynamic stability. Ions, atoms, and molecules collide, combine and rearrange in efforts to achieve as low an energy status as possible.
In the chemical world, there are a few contributors to instability: the first to consider is charge separation. When a molecule has a charge (being ionic, in that case), or has polar bonds which create partial positive and negative charges, that molecule is said to be reactive, and that molecule will “do” certain things to minimize that condition.
The second main factor that contributes to instability is the lack of an octet of valence electrons. Atoms will either readily donate electrons, accept electrons, or share them in efforts to acquire that perfect octet. The exception for our purposes to this rule is hydrogen, which follows the duet rule.
Since thermodynamic stability is a large driver of chemical reactions, it will be very important for you to be able to interpret energy diagrams which typically plot energy on the y-axis and various other factors along the x-axis (such as internuclear bond distance, time, molecular structures, etc).
If you can understand the processes that drive stability, then you will be able to look at a pair of reactants, reaction conditions, and from this understanding predict with accuracy the products that will result. This understanding will replace the needless hours spent in rote memorization. In addition, you will gain some significant life skills that will help you in your career as a medical professional or chemical engineer.
For class on Thursday, print out the below Lab 2 - Formal Charges. I think we can complete it during class time.
Plan for your success For every week, please read the the Weebly site from top to bottom, and check off items in the check off list provided as you complete them. In being this thorough, you can be sure you are fulfilling all the requirements for the course and your future success!
Check-off List of Things to Do:
In order to be adequately prepared for classes next week, please make sure you do the following by: Tuesday, August 31st, 2021
Watch the videos up to Section 1.8, if you need to
Bring to class Chapter 1 Homework so you can answer homework problems as we solve them in class
Thursday, September 1st, 2021
Print out, read, and bring to class: Lab 2 - Formal Charges (linked above)
Prepare for Quiz #2, covering material from Tuesday
Watch the course videos linked at right if you need them as a review!