As with friends, families, and communities, the truly interesting behavior starts once bonding has occurred and the structure is in place. The relationship dynamic for electrons is called “Valence Shell Electron Pair Repulsion”, which is a term that will never be hashtagged ever. VSEPR means that once electrons have bonded to form pairs, they move as far apart as possible from other electron pairs. This gives rise to many different structures as the pairs jockey for space. It’s important to remember that these structures are three-dimensional even though we draw them with dots, arrows and equations.
For example, the molecule SCL4 has five electron pairs around the S atom which creates a Trigonal Bipyramid like this:
The molecule XeF4 has six electron pairs around the Xe atom which creates an Octahedral structure that looks a lot like the jacks that we used to play with:
I learned 10 structures this week, ranging from the lowly Linear, Bent, and T-Shape all the way to the magnificent Tetrahedral and Square Pyramidal. I also learned that these bonds build more than just beautiful structures. The nature of the bond has a direct effect on the physical properties of the compound. Strong bonds cause high melting points, high boiling points, and low vapor pressures. I wonder what new materials are out there waiting to be created with just the right combination of structure and strength?
Tomorrow I am travelling to attend a conference about learning. I hope to eventually build just the right classroom combination, even though right now the areas of teaching and learning seem more like alchemy – all mystery and magic – and less like the balanced and predictable study of electrons that I find so comforting.
Next Up: Name and Number, Please
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- Molecular Geometry and the VSEPR Theory (joshfarha.wordpress.com)
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- ‘August: Osage County’ director John Wells on family dynamics (latimes.com)
