CH14 Notes Part 3

CH14 Notes Part 3 - Chapter 14 notes part 3: MOLECULAR...

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Chapter 14 notes part 3: MOLECULAR ORBITAL THEORY: Wavefunctions, like waves, can INTERFERE. Two main results: CONSTRUCTIVE and DESTRUCTIVE (Fig 14.27, BONDING ORBITAL ψ = ψ A1s + c B ψ B1s Atomic orbital wavefunctions constructively interfere. SIGNS of the wavefunctions are the same. ANTIBONDING ORBITAL ψ = ψ A1s - c B ψ B1s Atomic orbital wavefunctions destructively interfere. SIGNS of the wavefunctions are different. TWO AO’s ALWAYS PRODUCE ONE BONDING + ONE ANTIBONDING MO. BONDING MO: stabilizes the overall molecule. LOWER IN ENERGY, MORE STABLE THAN THE AO’s IT WAS MADE FROM. ANTIBONDING MO: destabilizes the overall molecule. HIGHER IN ENERGY, LESS STABLE THAN THE AO’s IT WAS MADE FROM. Sigma MO’s from two ‘ s’ AO’s: Mark in the NODAL PLANES!! We can use this to draw MO diagrams for homonuclear diatomics involing He and H (BRING SCRATCH PAPER TO CLASS!!) GENERAL METHOD: MO DIAGRAMS FOR HOMONUCLEAR DIATOMIC MOLECULES / IONS 1.Select & draw appropriate MO diagram. 2.Count TOTAL number of valence electrons. 3.If an ION, adjust the number of valence electrons (see example in class) 4.Fill in MO diagram using SAME principles as for single atoms: lowest first (AUFBAU), degenerate singly (HUND), no more than 2 electrons per LCAO-MO (PAULI) 5.Write the electron configuration using the MO’s instead of the AO’s BOND ORDER AND STABILITY: bonding MO’s stabilize; antibonding MO’s destabilize Relative occupancy of each determines how stable the molecule is: BOND ORDER = (# of BONDING electrons) - (# of ANTIBONDING electrons) 2 FRACTIONAL BOND ORDERS ARE POSSIBLE! Usually
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This note was uploaded on 11/09/2010 for the course CH 301 taught by Professor Fakhreddine/lyon during the Fall '07 term at University of Texas.

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CH14 Notes Part 3 - Chapter 14 notes part 3: MOLECULAR...

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