Lecture #11, Wednesday, January 27th

The main point I have been trying to emphasize to everyone this quarter is to think like a chemist. The tough part about chemistry is that in order to excel at it you need excellent critical thinking and problem solving skills. If you have these skills you will not only be able to use them in this class, but also all of your other classes and you future job(s). The rest of this unit in transition metal chemistry will focus on developing your critical thinking skills.

Our eyes are a complex instrument and are able to detect color in the wavelength range of 400 - 700 nm. In reality, this is just a tiny portion of the electromagnetic spectrum, and we can analyze all the other forms of radiation using advanced scientific instrumentation. The instrument we will focus on in this class is the UV-Vis spectrometer, which can detect radiation in the visible and ultra-violet regions in the spectrum. We can then use this information to analyze the electronic structure of molecules and complex ions. And by electronic structure, I mean how the electrons fill their orbitals, and how much energy it takes to excite electrons from orbital to orbital.

In order to interpret UV-Vis spectra properly and analyze electronic excitations between molecular orbitals, we first need to identify the interactions between orbitals, or how the orbitals overlap. Therefore it is VITAL to know the shapes of the orbitals (in 3-dimensions with phases) and how they are derived. The tutorial shown here will help you do this.

When molecules form they will do anything they can to get all their electrons in the lowest energy possible. To determine the energy, we must analyze the interactions the central atom has with all of its ligands as a unit.

The stronger a bond is, the more stable it is. This lowers the overall energy.

The greater the orbital overlap, the stronger the bond, and the more stable the bonding molecular orbitals become. For a tutorial and overview and a review of what was taught in general chemistry covering molecular orbital theory check this site.

We will be using the topics in those tutorials and taking them one step farther by analyzing the d orbitals in this class. I also posted a handout on carmen discussing molecular orbitals, bonding, MO diagrams, and color. Be sure to read through it.