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What’s coming up???

What’s coming up???. Oct 25 The atmosphere, part 1 Ch. 8 Oct 27 Midterm … No lecture Oct 29 The atmosphere, part 2 Ch. 8 Nov 1 Light, blackbodies, Bohr Ch. 9 Nov 3,5 Postulates of QM, p-in-a-box Ch. 9 Nov 8,10 Hydrogen and multi – e atoms Ch. 9 Nov 12 Multi-electron atoms Ch.9,10

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What’s coming up???

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  1. What’s coming up??? • Oct 25 The atmosphere, part 1 Ch. 8 • Oct 27 Midterm … No lecture • Oct 29 The atmosphere, part 2 Ch. 8 • Nov 1 Light, blackbodies, Bohr Ch. 9 • Nov 3,5 Postulates of QM, p-in-a-box Ch. 9 • Nov 8,10 Hydrogen and multi – e atoms Ch. 9 • Nov 12 Multi-electron atoms Ch.9,10 • Nov 15 Periodic properties Ch. 10 • Nov 17 Periodic properties Ch. 10 • Nov 19 Valence-bond; Lewis structures Ch. 11 • Nov 22 VSEPR Ch. 11 • Nov 24 Hybrid orbitals; VSEPR Ch. 11, 12 • Nov 26 MO theory Ch. 12 • Nov 29 MO theory Ch. 12 • Dec 1 bonding wrapup Ch. 11,12 • Dec 2 Review for exam

  2. COMBINING ORBITALS TO FORM HYBRIDS HYBRIDIZATION : the combination of two or more “native” atomic orbitals on an atom to produce “hybrid” orbitals the number of atomic orbitals that are combined must equal the number which are formed RULE: All resulting hybrid orbitals are identical.

  3. Note that these are +ive on one side of origin and -ive on the other!

  4. HYBRIDIZATION Combine one s and one p a sp- hybrid + ADD the orbitals + 2s+ 2p

  5. + The positive part cancels negative part + DESTRUCTIVE INTERFERENCE The positive part adds to positive part CONSTRUCTIVE INTERFERENCE 2s+ 2p

  6. Combine one s and one p to give an sp- hybrid 2s+ 2p + REMEMBER IF WE MIX TWO WE MUST GET TWO BACK The other combination is s - p

  7. + + The positive part adds to positive part 2s- 2p CONSTRUCTIVE INTERFERENCE The positive part cancels negative part DESTRUCTIVE INTERFERENCE

  8. 2s- 2p + We get two equivalent sporbitals ORIENTED AT 1800

  9. sp-HYBRIDIZATION The s and p orbitals The two sp-hybrids Directed at 1800

  10. COMBINE one s-orbital and two p-orbitals Get three sp2 - orbitals oriented at 1200 The s and p orbitals The three sp2-hybrids Directed at 1200

  11. COMBINE one s-orbital and three p-orbitals Get three sp3- orbitals oriented at 109.50 Back to methane

  12. H C H H H METHANE: CH4 four hybrid orbitals needed to form four bonds s + px + py + pz 4 sp3 hybrids An atom with sp3 hybrid orbitals is said to be sp3 hybridized The four sp3 hybrid orbitals form a tetrahedral arrangement.

  13. When orbitals are hybridized they have the same energy: HYBRIDIZE 2p sp3 E E 2s Orbitals in free C atom Hybridized orbitals of C atom in methane The FOUR sp3 hybrids are DEGENERATE. sp3 hybridization…….

  14. sp3 HYBRIDS C sp3 orbitals Now form the bonds to the H-atoms……...

  15. C s bonds Each bond in methane results from the overlap of a hydrogen 1s orbital and a carbon sp3 orbital. Hydrogen 1s orbital Carbon sp3 orbitals H Form a chemical bond by sharing a pair of electrons. H H H

  16. VALENCE BOND MODEL Hybrid orbital model Step 1: Draw the Lewis structure(s) Step 2: Determine the geometry of the electron pairs around each atom using VSEPR picture of molecular shapes Step 3: Specify the hybrid orbitals needed to accommodate the electron pairs on each atom

  17. AMMONIA: NH3 N H H H Electron pair geometry is tetrahedral Need sp3 hybrids

  18. sp3 hybrids on N in AMMONIA N H H H

  19. O H H WATER Overlap of two of oxygen sp3 hybrids with ….. Lone pairs in two of the sp3 hybrids. H atom 1s orbitals. To form two  bonds. Think about H3O+ !!!

  20. O H H HYDRONIUM ION. ISOELECTRONIC WITH …..? NH3 H+ ion: empty 1s orbitals. H+

  21. H H C C H H trigonal planar electron pair geometry around each C-atom. VSEPR a HCH angle of 1200. three hybrid orbitals on each carbon for the trigonal planar electron pair geometry 3 sp2 hybrids s + px + py The CARBON is sp2 hybridized The 3 sp2 hybrid orbitals form a trigonal planar arrangement. sp2 hybridization 3 effective electron pairs Ethylene: C2H4

  22. 2p 2p sp2 E E 2s FORMATION OF sp2 hybrids GROUND STATE C atom sp2 hybridized orbitals of C HYBRIDIZE This leaves one p orbital unhybrized…….

  23. An sp2 hydridized C atom z y x sp2 - hybrid orbitals UNHYBRIDIZED p- orbital The unhybridized p orbital is perpendicular to sp2 plane.

  24. H H C C H H BONDING IN ETHYLENE s bond z z y y C C x x OVERLAP the sp2 hybrids from the two carbons to form a sigma bond between them.

  25. The two unhybridized p orbitals are left over to form a ….. z z H H y y H H x x pi bond (p bond)

  26. H H C C H H

  27. BONDING SCHEME IN ETHYNE C C H H p:C(2p)-C(2p) TWO OF THESE!! s: H(1s)-C(sp) s: H(1s)-C(sp) s:C(sp)-C(sp) What does this look like????

  28. OVERLAP the C sp hybrids with H 1s to form sigma bonds z z C y y H H C x x

  29. LATERAL OVERLAP of p orbitals to form pi bonds. z z y y H H C C x x two pi bonds (p bonds)

  30. What about molecules with more than an octet around the central atom? Examples: PCl5, or SF4 or SiF62- etc….. Four orbitals Four pairs needs Five orbitals Five pairs needs six pairs needs six orbitals So??????

  31. Cl Cl Cl P Cl Cl PCl5 We ignore the chlorine atoms and just describe central atom. Need five hybrid orbitals on the phosphorus to fit the trigonal bipyramidal electron pair geometry d + s + px + py + pz 5 dsp3 hybrids 5 effective electron pairs dsp3 hybridization Five equivalent orbitals……..

  32. z y x dsp3 - hybrid orbitals TRIGONAL BIPYRAMID 900 1200 overlap with orbitals on chlorine to form 5 s bonds.

  33. F F F S F F F We ignore the chlorine atoms and just describe central atom. SF6 We need six hybrid orbitals on the sulfur 6 d2sp3 hybrids d + d + s + px + py + pz d2sp3 hybridization 6 effective electron pairs SIX equivalent orbitals……..

  34. z y x d2sp3 - hybrid orbitals 900 900 overlap with orbitals on flourine to form 6 s bonds.

  35. EXAMPLES Describe the molecular structure and bonding in XeF2 and XeF4 F F Xe 36 electrons … 8 bonding F F 4 x 6 on the F atoms … 32 used so 4 more on Xe 6 electron pairs about Xe … octahedral Square planar d2sp3 hybrids

  36. EXAMPLES Describe the molecular structure and bonding in XeF2 and XeF4 F Xe F 5 electron pairs …. Trigonal bipyrimid Molecule is linear dsp3 hybrids

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