Monday, September 3, 2007

2007 Welcome

This blog serves as a means by which students can ask anonymous questions related to the course material. How do you ask a question? It's easy - just click on "comments" and leave a note. It should appear on the blog promptly, and I'll generally answer within 24 hours. As the course goes on, I'll invite questions on the different chapters we cover.

17 comments:

Anonymous said...

First just wanted to say I'm really enjoying this class :)

How much does the waitlist usually move in this class? I am waitlisted number 4 and just really hoping to get in. Not as many people are dropping the course as I thought would.

How do you think my chances are?

Thanks alot

Scott McIndoe said...

Thanks. The waitlist will start to move more rapidly this week, especially after Wednesday when those students who have registered but haven't shown up are dropped. The waitlist for F02 is the longest (9.30 is a popular timeslot), but all of the waitlists eventually do drop to zero.
You should go and see Monica Reimer if you're unable to register for a lab because you are still waitlisted.

Anonymous said...

I signed up for the lab section of chem 101 since I was bumped off of the wait list! What exactly does the lab section consist of? It's 3 hours long!

Scott McIndoe said...

Check out your lab manual - it will describe what you're expected to do in each session. Do an experiment - write up a report.

Anonymous said...

I am guessing that you can purchase the lab manual at the bookstore?

Scott McIndoe said...

Correct; you also need a lab notebook - see the lab webpage for details.

Anonymous said...

Since I just got bumped off the wait list it does not matter if I missed the first lab?

Scott McIndoe said...

Ask Monica Reimer (dragon@uvic.ca), the senior lab instructor for the first year courses; she'll be able to give you the definitive answer.

Anonymous said...

Hello Dr. McIndoe, I've got a question on hybrid orbitals. When mixing a set of sp3d orbitals, is the d orbital always dz^2? Or is that just an example? (I ask because the movie clip used the same example and I don't know if this is always true or not.) Thanks

Scott McIndoe said...

Yes, it's always the dz2 orbital - if you mix any of the others with sp3, you don't get a trigonal bipyramid arrangement of hybrid orbitals (you can kind of see how the sp3d hybrids come about if you consider taking the 3 sp2 hybrids for the 3 equatorial orbitals then mixing the pz and dz2 to make the 2 axial orbitals).

Anonymous said...

Thanks for the reply. Is it energetically equivalent to mix another degenerate d orbital instead of dz^2? Even though you don't get a trigonal bipyramid structure.

Anonymous said...

I would like to ask about lattice energy. We did a lab where an increase in lattice energy facilitated crystallization in ethanol, but since ethanol is polar, how come the product forms a lattice structure at all instead of staying dissolved? The compound we made was tetramethylammonium triiodide. Is it because tetramethylammonium ion is big and less soluble so it "takes the iodide with it" and forms a lattice structure? Thanks

Scott McIndoe said...

Re: orbitals; you get an appropriate combination of orbitals to suit the environment of the atom. Consider carbon - if it has two neighbouring atoms only, it is sp, 3 sp2, 4 sp3 - it arranges its electron density to maximise overlap. Similarly, an atom's solution to the problem of bonding to 5 atoms arranged in a trigonal bipyramid about it is to hybridize sp3d(z2), and this is the energetically most favourable combination. See the Orbitron for more details if you're interested in the math.

Scott McIndoe said...

Re: Lattice energy. It's a delicate balance between solvation energy (the sum of all the forces between solvent and dissolved ions) and the lattice energy (the electrostatic attraction between ions). If you can get your ions to pack efficiently in the lattice, they will be able to get closer together and maximise the lattice energy (remember d, the ion spacing, is inversely proportional to the lattice energy). So, to make something crystallise preferentially, you pick a counterion that is a good size match and its solubility will drop.

Anonymous said...

Dr. McIndoe...today you said that if two atoms, one big one small, interacts, then dispersion forces dominate over dipole-dipole forces. Why is this? Thanks for your answer.

Scott McIndoe said...

Your notes say "If two molecules are of comparable size and shape, dipole-dipole interactions will likely be the dominating force with respect to intermolecular attractions BUT if one molecule is much larger than another, dispersion forces will likely determine its physical properties". So while acetonitrile (large dipole moment) has a higher boiling point than propane (near-zero dipole moment) due to dipole-dipole interactions, if you compare acetonitrile to octane (a longer-chain hydrocarbon than propane), the sum of all those dispersion forces in this larger molecule means that despite the lack of dipole-dipole forces, octane has a higher boiling point than acetonitrile.

Anonymous said...

Hey Dr.McIndoe, I know this isn't related to the lecture portion but I was wondering...this week we made soap in our labs and after we let the fat react with the NaOH we placed the resulting mixture into NaCl...was this just to precipitate the soap? did the charged portion of the soap (+) interact somehow with the CL- ions? thanks for your time.