Molecular polarity

Today we talked about how VSEPR structures can be used to predict macroscale physical properties. The biggest property to look for is molecular polarity. If a molecule or ion has polar bonds that do not all cancel themselves out, the molecule or ion is polar. This influences a number of different properties from melting/boiling point to solubility.

Keep on practicing those Lewis and VSEPR structures. Maybe during your Thanksgiving dinner you could use peas and mashed potatoes to build a series of Lewis structures, then construct VSEPR models using marshmallows and pretzels. Teach your younger siblings and cousins about the repulsive interactions between electrons and the difference between LP-LP, LP-BP and BP-BP interactions. Don't just have a Thanksgiving, make this year a Thinksgiving!

Either that, or just eat too much, visit with family and friends, and relax a bit so you're ready to take on the last couple weeks of the semester.

Have a great weekend, and I'll see you all on Monday.

Drawing VSEPR and those troublesome lone pairs...

Today we talked about drawing VSEPR structures and the shapes that result from structures that contain lone pairs. The shapes and angles are all a result of lone pairs (LPs) being "bigger" than bonding pairs (BPs), meaning that LP-LP interactions are more intense than LP-BP interactions which are more intense than BP-BP interactions.

Don't forget about your current Mastering Chemistry assignments, Assignment 18 is due Saturday, Assignment 19 is due Tuesday.

Again, for students in all of my lab sections, your Iron Ore hand in is due by noon next Tuesday, November 25th.

Have a good weekend, I'll see you all on Monday.

"Other" elements in Mastering Chemistry

A number of people have run into the problem of entering elements other than those listed in the pop-down menu when drawing Lewis structures in Mastering Chemistry. If you need an unlisted element (like, perhaps, Si...), you can draw a carbon (or any other element) then double click on the "C". At that point, you should be able to type in the symbol of whatever element you need. This actually works for any element, so if you want to draw your entire skeleton structure in using the default element (carbon) and then double click your way through to change elements to O or F or whatever else, you can do that.

VSEPR

Today was our first big VSEPR day. We went over the electronic geometries associated with 2-6 regions of electron density (2 R.E.D. = linear; 3 R.E.D. = trigonal planar; 4 R.E.D. = tetrahedral; 5 R.E.D. = trigonal bipyramidal; 6 R.E.D. = octahedral) including the bond angles predicted by each of these geometries. This is a pretty big topic/concept, and the only way you'll get good at is by looking at and working through examples. The best thing you can do is look back over your class notes and study notes and every time you find a molecule, draw out a Lewis structure and assign a VSEPR electronic geometry. We'll be spending at least another day on this (probably 2 or 3).

For all of my lab students, your Fe ore hand in is due by noon next Tuesday. If you are in one of Dr. Marasinghe's labs or Dr. Edvenson's lab, check with your instructor for deadlines on this and all assignments.

Wrap up Chapter 9

We cleaned up a few topics today including bond length and strength trends, using bond strengths to estimate {delta}H for a reaction, and using the Bond-Type Triangle to predict the type of bonding in binary compounds. We also just barely started talking about VSEPR, we'll probably spend the rest of the week and next week on VSEPR.

Drop-in tutoring/help is available in HA405 at the following times:
Monday 3-4:30pm {Amber Goraczkowski}
Tuesday 11:45am-1pm {Eric Berget}
Wednesday 2-3pm {Joelle Rolfs}

There's a new MC posted, this one has a few more questions than the last couple, so don't wait to get started on it.

Friday, Friday, Friday....

Today we looked at some more examples of resonance and used bond order to describe bonds that are resonance averaged.

The Chem Club is organizing drop-in tutoring for Gen Chem. These will be people who were successful in Gen Chem and are offering their assistance to you. Drop-in tutoring is informal, there is no set "lesson" and you don't need to sign up or register, just stop in if you have questions. For now, sessions will be held in HA405 on Mondays at 3-4:30pm {Amber Goraczkowski} and Tuesdays 11:45am-1pm {Eric Berget}. More times may become available, I'll post any information I get here on the blog.

There's a new MC, due Tuesday.

Have a good weekend, I'll see you all Monday.

Lewis structures

Today we worked through a couple examples of Lewis structures and looked at the concept of formal charge as a way to decide whether a Lewis structure is "good". We also looked at resonance structures and talked about electronegativity as a way to decide how molecules and polyatomic ions should be assembled. Lewis structures are extremely useful tools and require a bit of practice, so don't wait to practice them.

A new MC assignment is posted.

Atom/Ion size and bond types

Today we wrapped up trends in ionic radius compared to neutral atoms and started talking about different types of chemical bonding. We just started looking at Lewis structures as a tool which will help us understand covalent bonding, and we'll continue with more Lewis structures throughout the rest of this week. In all cases, we're looking at how atomic/periodic structure can help us predict macroscopic behavior and properties.

More electron configs and periodic trends

Today we talked about a couple more periodic trends and how they relate to the electron configuration of the atoms and/or ions involved. We talked about magnetism, ionization energy and electron affinity. We also looked at a problem set in class that should show us the trend in ionic size/radius for either cations or anions. It didn't seem like most people made it through the whole problem set in class, so be sure to take a look at it over the weekend and we'll wrap that one up in a couple minutes at the beginning of class on Monday.

There's a new Mastering Chemistry posted, due Tuesday. Don't forget the current MC assignment, due tonight.

Don't forget the "Diggin for a Cure" volleyball game tonight, the team also plays tomorrow afternoon. If any other teams, groups, or organizations would like me to mention their events on the class blog, let me know. I'm always interested to know what people in class are involved in.

Electron configs and periodic properties

Today we discussed quantized energy levels and looked at a few more electron configurations. We also began to look at how electron configurations could be used to predict the properties of elements. We looked at atomic size/radius, we'll continue to look at other properties over the next couple days.

Chem Club meeting TONIGHT at 7:30pm in SL104.

I'll also make another specific pitch here for SI. The tools we're using right now (quantum numbers, electron configurations, etc) become much easier to work with if you practice, practice practice them. SI is an excellent opportunity for you to practice some of these things in an environment where you can help others and they can help you. Don't wait until the week before the next exam to work on these things.

Finally, this Friday night the MSUM volleyball team will be "Diggin for a Cure". The game starts at 7pm and the Dragons will be wiping the floor with St. Cloud State. Wear purple to show your support, T-shirts will be on sale ($10) at the game or in the MSUM Athletics Office. Come out to Nemzek to cheer on the team and support this worthy cause.

From light waves to atomic orbitals

Sorry I didn't get this up sooner, something came up yesterday.

Monday in class we transitioned from our discussion of light and waves to the behavior of electrons. This is partially explained by deBroglie's relationship which describes the wave-like character of moving electrons. Since chemistry is all about electrons, we needed a system to address individual electrons in an atom so we talked about quantum numbers and began to look at how we could use a shorthand version of quantum numbers (called electron configurations) to begin to predict properties of elements. We'll pick up there on Wednesday.

There is a new Mastering Chemistry assignment posted, due Friday. The monthly Chem Club meeting is also being held this week, Wednesday night at 7:30pm in SL104.

The nature of light....

Friday in class exams were returned. The average was up a bit (around 120/150) on the exam, and now that we have 3 exams in the books we can start making a little more informed projection of course grades. Given the current scores and distribution, if I drop everyone's lowest exam score it looks like the syllabus grade cutoffs are appropriate: 90.0% for A's, 80.0% for B's, 70.0% for C's, 60.0% for D's. I typically use +/- grades, so if you're are the very top or bottom of one of those ranges you will likely see a + or -. We still have 1 regular 150pt exam and a 200pt final exam and a few more Mastering Chemistry assignments, so there are quite a few points still out there to be earned (or lost). As a point of reference, the class is worth 750pts total. Add up your 2 highest exam scores and your current percentage in Mastering Chemistry to see how many more points you have to earn to reach your goal grade. An A will probably require >675pts, B>600pts, C>525pts, D>450pts.

We also started talking about the nature of light as described in Chapter 7. I didn't go over every little detail, your textbook does a fine job of that. We'll put that discussion of light into an atomic context Monday in class.

Have a good weekend and don't forget to set your clocks back on Saturday night/Sunday morning.