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Molecules aren't flat. They're three dimensional, and that has implications for their physical and chemical properties. For example, X-ray crystallography labs at MIT determine the 3D shapes of protein molecules to design drugs that will fit into these proteins. In this video, you'll learn about an empirical model chemists use to predict a molecule's 3D shape from its Lewis structure. This video is part of the Representations video series. Information can be represented in words, through mathematical symbols, graphically, or in 3-D models. Representations are used to develop a deeper and more flexible understanding of objects, systems, and processes. Hi. My name is Cathy Drennan and I am a professor in the chemistry department at MIT. I hope you have been enjoying your general chemistry course at SUTD. After watching this video, you will be able to use the VSEPR model to predict 3D molecular structures from 2D Lewis structures and... ...discuss some of the...

PROFESSOR: The molecules and Born-Oppenheimer approximation. OK, we all know that molecules are a lot harder to solve than atoms, and even atoms are not that easy once you have more than one electron because of the electrostatic repulsion, but molecules are significantly different in that one of the greatest simplicities that we had with atoms is that the atom is such that the potential created by the nucleus is spherically symmetric. When you have a molecule you have separate nuclei and therefore your spherical symmetry is gone, and whether you have one electron or more than one electron, there is no spherical symmetry. All our tools of angular momentum don't help us much. We have to start the problem anew. So the difficulty with molecules is basically that the potential for the electrons, where they move is not spherically symmetric. There is another thing that helps us, however, is that there's a nice separation of mass scales. You have the mass, little m, of t...