Physical 4

Physical 4

1. LCAO

   • lowest energy
     • bonding-constructive
       • build up in electron density
         • strong interaction of electrons with nuclei
     • cylindrically symmetrical
     • sigma MO
   • highest energy
     • anti-bonding - deconstructive
       • depleted electron density
         • weak interaction of electrons with nuclei
           • cylindrically symmetrical
           • sigma* MO

2. ψ

   • large R
     • behaves like 2 independent AOs
   • small R
     • significant overlap of AOs

3. bonding

   • more electrons
     • stronger and shorter bond
     • electron repulsion
       • lower dissociation energy

4. light

   • waves & particle duality

5. electron waves

   • described by wavefunction
     • wavefunction describes the amplitude
   • stationary state
     • eigenstate
       • wavefunctions are eigenfunctions
       • energies are eigenvalues

6. orbital notation

   • identical sign
     • gerade
   • inverse sign
     • ungerade

7. orbitals

   • angular nodes
     • • sigma
         • greater constructive overlap
     • 1
       • pi
         • smaller separation

8. bond order

   • B=1/2(Nb-N*)
   • vibrational wavenumber is proportional to bond strength

9. Energy gap

   • large z
     • no significant interaction
       • normal ordering of energy
   • small z
     • mixing of MO
       • 1 sigma g destabilises2 sigma g

10. heteronuclear diatomics

    • large difference in electronegativity
      • MO close to AO has more AO character
    • small difference in electronegativity
      • determine energy gap by isoelectronic molecules

11. blue photon has more energy than red photons

12. excited state - decreases dissociation constant