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Bond Theories

Bond Theories. All about the ……? Lewis structure limitations Cannot show molecular shape – 2d Remember sublevels? Azimuthal shape S – 1 orbital P – 3 orbitals D – 5 orbitals F – 7 orbitals All because of electron repulsion. Bond Theories. Remember sublevels? Azimuthal shape

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Bond Theories

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  1. Bond Theories • All about the ……? • Lewis structure limitations • Cannot show molecular shape – 2d • Remember sublevels? • Azimuthal shape • S – 1 orbital • P – 3 orbitals • D – 5 orbitals • F – 7 orbitals • All because of electron repulsion

  2. Bond Theories • Remember sublevels? • Azimuthal shape • S – 1 orbital • P – 3 orbitals

  3. Bond Theories • Remember sublevels? • Azimuthal shape • D – 5 orbitals

  4. Bond Theories • Remember sublevels? • Azimuthal shape • F – 7 orbitals • All because of electron repulsion

  5. Bond Theories • Covalent bonds • 2 electrons with opposite spin sharing overlapping orbitals • Electrons available to both nuclei • Effectively both atoms acquire the shared electrons • Valence Bond Theory

  6. Bond Theories • Covalent bonds • Sigma and Pi bonds • Sigma ∂ bonds • Overlapping orbitals • S (side – side) or P (end-end) • Or P – S – in line

  7. Bond Theories • Covalent bonds • Pi (π) bonds • P orbitals out of plane are drawn to each other and overlap • Double and triple bonds

  8. Bond Theories • Covalent bonds • Pi (π) bonds • Triple bond in molecular nitrogen

  9. Bond Theories • Molecular Resonance • Many bonds can be represented by more than one lewisstruct. • Should be diff. between 2 ends due to double and single bonds – BUT NO!! • Completely symmetrical • Resonance • Electron wave function can occupy different regions of a molecule at same time • Example - Ozone

  10. Bond Theories • Odd # of valence electrons • Extra is free radical – cause damage to cells • Eat your fruits & veggies to combat

  11. Bond Theories • Fewer than 4 pairs • Boron – 3Ve – content with 6 to fill occupied orbitals – Boron trifluoride

  12. Bond Theories • Expanded octet • Extra electrons occupy empty d sublevels • Sulfur hexafluoride

  13. Bond Theories • What happens when theories don’t explain observations? • LOX

  14. Bond Theories • Time for a new theory • E.g. valence bond theory – prohibits stray electrons that account for certain properties of molecule – answer? Resonance structures • Also doesn’t account for properties of LOX • Thus – Molecular Orbital Theory • When bond forms, old orbitals replaced by totally new orbitals • Each molecule has unique orbitals – equal in # to what sum of orbitals in original atoms • Some encircle multiple atoms or entire molecule

  15. Bond Theories • Time for a new theory • Some encircle multiple atoms or entire molecule • S orbital hybridization

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