Quantum Chemistry in 3 lectures: lectures 1 and 2

This is the time of the year when I teach Quantum Chemistry and Statistical Thermodynamics to our second year class. I have 3.5 lectures for each, but usually do 3 lectures for each topic and use the extra lecture as a class problems session.

In this post I will concentrate on the challenge of fitting the important parts of Quantum Chemistry into 3 lectures, and will consider the first 2 of these lectures specifically. The third lecture will then be covered in a separate post.

So the first consideration is: what topics to cover? Most textbooks start their treatment of Quantum Mechanics with a discussion of the experiments whose analysis ultimately led to the development of the subject, and I have followed this path too. So Lectures 1 and 2 are really about the experiments that established the ideas of wave-particle duality, and in lecture 1 I consider the experiments that showed light to have particle properties, i.e. the Photoelectric Effect and the Compton Effect. Both experiments are described in detail, but this year I am hoping to include some video clips, where the experiments are actually demonstrated. Links to some selected clips will be added to my Facebook teaching pages, so anyone interested can easily find them and try them out themselves. For both the Photoelectric Effect and the Compton Effect I have included descriptions of experimental methods that have been developed based on them, namely Photoelectron Spectroscopy and the Compton Telescope. The aim here is to show that as well as helping to develop a new subject area, the experiments gave rise to useful methods for Chemistry and Gamma Ray Astronomy respectively.

So, in summary, lecture 1 confirms the ideas of photons and justifies the Planck relation for energy and frequency (E = hf). The students will have already met this in other modules, but to truly understand it, you need to look at the results of something like the Photoelectric Effect experiment.

Lecture 2 starts with the idea of wave-particle duality, and the de Broglie equation. The impressive thing about de Broglie’s work is that he predicted the wave properties of particles before they were demonstrated unequivocally in the Electron Diffraction experiment. I will describe Electron Diffraction, again hopefully including some video clips. I am also going to discuss whether diffraction is possible with larger ‘particles’, including C60 molecules. I got this idea from Chad Orzel’s excellent book ‘How To Teach Quantum Physics To Your Dog‘, which I have read recently, and which has been a great source of ideas for these lectures.

Having discussed the Electron Diffraction experiment, and reached the conclusion that the electron shows wave behaviour, it’s time to introduce the idea of wavefunctions. The students are already familiar with the idea of orbitals, but for the first time they will get a proper explanation of why they are used. So I introduce orbitals first, and use them to bring in wavefunctions. The idea of a wavefunction is a difficult one, but I hope that using orbitals as an illustration will help. The idea is that by the end of lecture 2 we know about orbitals, so that the calculation of wavefunctions by the Schrodinger equation can be introduced smoothly at the start of lecture 3!

If you would like to have a look at the lecture slides for this course, you can find them here.

Lecture 3 will be described in a post next week. I will also mention any good or bad points from lectures 1 and 2 for future reference.

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2 thoughts on “Quantum Chemistry in 3 lectures: lectures 1 and 2”

    1. Yes, sorry. My website was closed by Microsoft when they changed the ‘small business’ facility (:. I’m rebuilding my site, but haven’t put the lectures up yet. If you would like them, send me an e-mail to jacksonroba@gmail.com, and I’ll send them by return.

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