Molecular Orbitals

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Molecular Orbitals
I know, the comic doesnt fit
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Molecular Orbitals

• The nature and variety of electronic states are
  also more complicated than diatomic states
• Molecular Orbitals - Linear Combination of
  Atomic Orbitals (LCAO) MOs
• Although the classification of a molecular
  orbital as s or p is strictly valid only for
  linear molecules, it is also used to denote the
  local symmetry with respect to a given A-B bond

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http//www.sparknotes.com/chemistry/bonding/molecu
larorbital/section1.html
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Polyatomic Orbitals

• More generally, the electronic states of
  polyatomics are described in terms of the overall
  symmetry of the molecule
• Symmetry Adapted Linear Combinations - SALCs

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http//employees.csbsju.edu/hjakubowski/classes/ch
123/Bonding/vsepr.gif
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Molecular Orbital Theory for Polyatomic Molecules

• 1) Assume 1 electron atomic orbitals (AOs) serve
  as a good basis wave functions
• 2) Generate molecular orbitals (MOs) by the
  Linear Combination of Atomic Orbitals (LCAOs)
• 3) Generate molecular electronic configurations
  by adding electrons to each MO (two at a time in
  accord with the Pauli Exclusion Principle)
• 4) Get the lowest energy electronic configuration
  (ground electronic state) by filling only the
  lowest energy orbitals
• 5) Get excited state configurations by adding
  electrons to excited orbitals (e.g. antibonding
  orbitals)

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http//www.sccj.net/publications/JCCJ/v5n3/a81/tex
t.html
http//www.cem.msu.edu/reusch/VirtualText/intro3.
htm
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Six atomic orbitals (4 on the oxygen, 1 each from
the two hydrogens) must combine to form six
molecular orbitals. Since there are only two
bonds in the molecule, there can only be two
bonding MO's (and two antibonding MO's). Two of
the sp3 hybrid orbitals on oxygen are not
involved in bonding - they are nonbonding, and
their energies will stay the same. The MO's are
then filled with the 8 electrons 4 go in the
s -MO's and 4 go in the n-MO's.
                                                  
                                                
The atomic orbitals that one uses for the
construction of molecular orbitals are chosen
based on the known geometry of the molecule.
Thus, the choice of sp3 hybrid AO's for oxygen
was made because the H-O-H bond angle is 104.5o,
close to the tetrahedral angle. One would choose
to use sp hybrids only when the molecule is
linear.
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MOs for water
MOs for benzene
http//www.lsbu.ac.uk/water/h2oorb.html
http//www.chem.ucalgary.ca/courses/351/Carey5th/C
h11/ch11-4-1.html
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Atomic Emissions