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Molecular Orbital Theory applied to NH3

    NH3, also known commonly as Ammonia, is a colorless gas that carries with it a pungent smell. It hydrogen bonds extremely well due to the fact that it has an accessible lone pair, making it miscible with water. It has a molecular configuration of trigonal pyramidal and with its lone pair experiences a dipole moment making the molecule polar.

    1. 1. Introduction
    2. 2. Molecular Orbital Diagram
    3. 3. Symmetry Elements
    4. 4. Character Table
    5. 5. References
    6. 6. Outside Links
    7. 7. Problems
    8. 8. Contributors

    Introduction

    Molecular Orbital Theory builds on the aspects of VSEPR Theory, VB Theory, the Pauli Exclusion Principle and Hund's Rule to explain how valence electrons fill in each molecular orbital. The Molecular Orbital Theory explains, for polyatomic molecules, how hybridization occurs. Molecular Orbital Theory has advantages over VB Theory in that it can explain para/dia-magnetic properties of molecules and easily deduce their bond orders from the coinciding molecular orbital diagrams.

    Molecular Orbital Diagram

    NH3 has 8 valence electrons. As was already discussed there is one lone pair and 3 N-H bonds resulting in a trigonal pyramidal shape. Based on knowledge of Molecular Orbital Theory we fill the orbitals to obtain the lowest possible energy. Resulting in 2 paired electrons in the σ2s, σ*2s,...

    (PICTURE HERE: MO Diagram)

    Symmetry Elements

    With the resulting predicted trigonal pyramidal shape we can find the primary axis of rotation to be a C3 , and there are 2 C3's. We also can see 3σv's along the N-H bonds.

    (PICTURE HERE: Symmetry elements trig planar model)

    Character Table

     

    C3v E 2C3 3σv Linear Rotations Quadratic
    A1 1 1 1 z x2+y2,z2
    A2 1 1 -1 Rz  
    E 2 -1 0 (x,y)(Rx, Ry) (x2-y2, xy)(xz,yz)

     

    References

    1. This is meant for references used for constructing the module. They must be primary and accessible to readers at a library.        
    2. You need at least two different sources here. Websites are not allowed. DOI links to J. Chem. Ed. are ideal Do not reference class notes. Also, do not reference textbooks for maximal credit. Using the insert citation button to automatically handle references is highly suggested (bottom right button on editor toolbar).

    Outside Links

    • This is not meant for references used for constructing the module, but as secondary and unvetted information available at other site
    • Link to outside sources. Wikipedia entries should probably be referenced here.

    Problems

    1. What are the benefits of using MO theory over VB theory?
    2. What is the predicted molecular geometry based on VSEPR?
    3. Based on the MO diagram what is NH3 paramagnetic or diamagnetic?
    4. Based on the MO diagram what is the bond order for NH3?
    5. What is NH3 point group characterization?

    Be careful not to copy from existing textbooks. Originality is rewarded. Make up some practice problems for the future readers. Five original with varying difficulty questions (and answers) are ideal.

    Contributors

    • Name #1 here (if anonymous, you can avoid this) with university affiliation
    • Name #2 here with university affiliation

    Tags below. If no tags exist, then add two new ones: "Vet1" and the level of the module content (e.g. "Fundamental"). See FAQ for more details.

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