# HW #1, Conference assignments, Study guide #2

I’ve been inundated with questions and comments about homework assignment #1, and requests for changes in conference assignments, so I wanted to bring you up to date on these and other items of interest.

1. The study guide for Chapter 2 has been posted online. We will start coverage of this chapter tomorrow.
2. I will be working on requests/volunteers for conference changes tomorrow and contact those involved by email tomorrow.
3. Homework assignment #1 lists several problems from Loudon: 33,
39, 45, 47. These are all from chapter #1 and should have been listed
as 1.33, 1.39, 1.45, 1.47 to eliminate any possible confusion. (Note:
some of the problems in Loudon are not solved in the Solutions Guide, but if you can find a solution to a homework problem in the Guide, the usual “own your work” rule still applies.)
4. I will be talking some more about molecular orbitals tomorrow (Wed) and this will help with problem #3.
5. The questions relating to cyanamide on homework #1 have
generated some intense discussion, all of it justified. Let me try to
steer you through these issues, problem by problem.
• Problem 1 asks for a Lewis structure of cyanamide, but some of you have correctly detected that cyanamide is a resonance hybrid, so what should your answer be? Please give me one legitimate Lewis structure for cyanamide. Those of you looking at two or more resonance structures, should just give me the structure with the greatest weight.
• Problem 2 asks you to predict bond angles based on your Lewis structure. I am mainly interested in how you get from a Lewis structure to a bond angle prediction, so whichever structure you draw in #1, that’s what you should use to predict bond angles in #2 (now you can see why it is important to draw only one Lewis structure in #1).
• Problem 3 suggests making two drawings of cyanamide and drawing an orbital on each. First, I want two drawings so that the orbitals don’t have to be combined on a single drawing (that would confuse me). Second, each orbital extends over a particular region of space and I’m interested in seeing where you believe that region to be. For that reason, I want you to draw a wedge-dash formula that provides a 3-D geometry for the molecule. The molecule will serve as my reference point in guessing the location of your orbital. Third, I suggest that the two drawings might adopt different perspectives with regard to the molecule. The reason? The two orbitals point in different directions, so if both formulas use the same perspective it might be easy to draw one orbital, but ratherhard to draw the other. I recommend orienting the molecule in each drawing so that the orbital’s symmetry axis lies in the plane of the paper.
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