You may or may not remember learning about the periodic table in chemistry class and why it's shaped the way it is. Dr. Preston MacDougall explains the orbital model that's behind it, and why orbitals are actually just invented mathematical entities.

Tune in to learn the following:

• Why it's significant to understand the difference between the orbital model and the probabilistic model of electron behavior in chemical bonds and reactions
• How the vibrational timescale of molecules poses barriers to experimentation, and the complex process by which chemists collect x-ray diffraction data and view molecules vibrating in zero-point motion or harmonic mode
• What role non-contact enzymes or catalysts play in chemical reactions

Preston J. MacDougall, Ph.D. is an author and professor at Middle Tennessee State University, and returning guest on today's episode. He begins by explaining the orbital model, which he says is a convenient model for teaching early students of chemistry how to understand electron configurations and why the periodic table is organized in the way that it is.

However, he says that orbitals are actually just mathematical entities that do not apply to anything but single electrons. Why? Dr. MacDougall explains that it's because the orbital model assumes that an individual electron is not influenced by the motions of all of the other electrons around it.

As opposed to the orbital model, Dr. MacDougall prefers to consider the probabilistic picture, which is that every electron in an atom has a certain probability of being found at a certain point around the nucleus at any given time. This is referred to as the charge or cloud density, and he explains how it changes with relation to the proximity of the electron to the nucleus of the atom.

He continues by discussing the vibrational timescale of molecules, which is less than a trillionth of a second. So, how is it that scientists conduct experiments on molecules that vibrate so quickly? He explains the method of obtaining x-ray diffraction data, which begins by the cooling of crystals with liquid nitrogen or liquid helium until they reach a temperature of about -250 degrees Celsius.

At that point, molecules reach the lowest possible energy state of zero-point motion, where chemists can then "deconvolute" the electron cloud and make it appear as though a molecule is standing still. Dr. MacDougall expounds on the ways in which the pressure produced by atoms on other atoms can be modified to produce electron cloud changes, explains the octet rule and stability of noble gasses, touches on the applications of quantum chemistry and molecular modeling in drug design, and so much more.

To learn more, visit https://www.mtsu.edu/faculty/preston-j-macdougall.