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  Home > JCE Print > Journal of Chemical Education > Issues > 2004  > July  >
In the Classroom
Moving Beyond the Single Center—Ways To Reinforce Molecular Orbital Theory in an Inorganic Course
Marion E. Cass and William E. Hollingsworth
Department of Chemistry, Carleton College, Northfield, MN 55057
Cover
July 2004
Vol. 81 No. 7
p. 997
Abstract
Rather than ending the discussion of molecular orbital (MO) theory in an inorganic chemistry course with molecules such as octahedral ML6 or square planar ML4, we suggest moving beyond the single-atom center to include the MO diagram of ethene (C2H4). Embracing the use of group theory and symmetry adapted linear combinations (SALCs) at the level already taught, we extend the coverage to include this simple organic dimer as a means of teaching skills that enable students to tackle significantly more complicated molecules. Ethene provides a bridge to the fragment approach pioneered by Roald Hoffmann and used in some high-level treatises. Larger molecules are split into component fragments poised to form bonds. The MO diagram is constructed for each fragment and then combined to obtain the MO diagram of the full molecule. In this way, more sophisticated examples can be addressed if the process is reduced to smaller, more chemically intuitive steps. To bring the fragment approach to the undergraduate curriculum, we present the MO diagram of C2H4 first using SALCs of atomic orbitals and then contrasting this with a two-step fragment approach that first creates the MO diagram of the CH2 diradical.
Supplement
The following are available:
  1. Notes on Selected Texts and References for Teaching MO Theory
  2. Symmetry Analysis for H2O (to Create SALCs and Assign Symmetry Labels for Atomic Orbitals that will be used in Bonding)
  3. Mixing Among the A1 Orbitals of H2O: Differing Points of View
  4. A Comparison of the Energies of the MOs of Water Calculated with Our Molecular Modeling Program (Under Different Basis Sets) versus Those Determined from Photoelectron Data
  5. Class Assignment Comparing the Similarities and Differences Among Seven Selected MO Diagrams for Water
  6. Atomic Orbital Energies for the First 18 Elements
  7. Spartan Output from the MO Calculation on CH2
  8. Symmetry Analysis for C2H4 using a SALC Approach
  9. Symmetry Analysis of C2H4 MOs using a Fragment Approach
*  Contents JCE2004p0997W.doc (Microsoft Word)
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More Information
*  Citation
 Cass, Marion E.; Hollingsworth, William E. J. Chem. Educ. 2004 81 997.
*  Keywords
 Bonding Theory; Inorganic Chemistry; MO Theory; Molecular Modeling / Dynamics
*  History
 Created:
Last Updated:		 May 27, 2004
January 19, 2005
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