What’s coming up???

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. Electron cloud probability distributions for different types of bond

4. Dipole moment will align molecules in an electric field

6. O O O N Nitrate anion NO3- Put a pair between each atom nitrogen does not have noble gas structure!!! form a double bond by sharing a pair from one of the oxygen atoms……….

7. - O O O O O O N N - - O O O N FORM A DOUBLE BOND BETWEEN O AND N Here is one Here is another! Here is another!

8. O O O - O O O N Experiment shows all three bonds are the same. All bond lengths 128 pm N All bond angles 120 0 Any one of the structures suggests one is different! Double Bond Single Bond Should be different! So…….

9. O O O O O N N N O O O O RESONANCE We use a double headed arrow between the structures.. The electrons involved are said to be DELOCALIZED over the structure. The blended structure is a RESONANCE HYBRID

10. F F F S F F F - I I I Elements in rows 3 and following can exceed the octet rule: When it is necessary to exceed the octet rule the extra electrons go on the central third row element. S … 12 SF6 CentralI … 10 I3-

11. FREE RADICALS O N O O N O Molecules which have unpaired electrons. NO2 Is a free radical Total number of valence electrons = 5+6+6 = 17 O N O Form double bond to get N close to octet RESONANCE

12. H O H PREDICTING THE SHAPES OF MOLECULES from the Lewis electron dot structure using the principle that electron pairs stay as far apart as possible. BOND PAIRS Electron pairs LONE PAIRS

13. VALENCE SHELL ELECTRON PAIR REPULSION: VSEPR Based on the idea that all electron pairs repel each other. The bonding and lone pairs push apart as far as possible…….. This means that atoms bound to a central atom are as far apart as possible……. we can find the molecular shape! Lets see how it works…...

14. My currents interests are in the field of Molecular Geometry. I have long been interested in further developing the VSEPR model and at the same time trying to understand why certain molecules appear to be exceptions to the model. Partly in collaboration with my colleague Richard Bader, I have been making use of the analysis of calculated electron density distributions to better understand the VSEPR model and molecular geometry in general. We have shown that the Laplacian of the electron density provides evidence for the localized lone pairs of the VSEPR model and we have developed the Lennard-Jones function which also provides evidence for lone pairs on a different basis.      One of the largest classes of exceptions to the VSEPR model are certain molecules of the transition metals. We have shown that the deviations of the geometry of these molecules from the VSEPR model can be related to the distortion of the metal atom core from a spherical shape which we have been able to study by means of the Laplacian electron density. This investigation is continuing. Recently I have shown that the intramolecular distance between two given ligands is remarkably constant over a wide variety of molecules which led me to suggest that interligand interactions are much more important in determining geometry than has previously generally been supposed. This observation has led me to develop the ligand close packing (LCP) model.

15. S S O O O O Resonance (like SO2) SeO2 O Se O LEWIS STRUCTURE SO2 Experiment shows that both S-O bonds are equivalent. We say that the real SO2 molecule is a hybrid of the two resonance forms.

16. O Se O Se SeO2 ELECTRON PAIR GEOMETRY THREE ELECTRON PAIRS AROUND THE SELENIUM ATOM. VSEPR treats double bonds like a single bond TRIGONAL PLANAR Now place the oxygen atoms

17. O Se O Se Se O O SeO2 Electron Pair Geometry is trigonal planar ADD OXYGENS SeO2 IS V-SHAPED, OR BENT

18. H H C H H There are four electron pairs around the carbon atom. CH4

19. C The best arrangement for four electron pairs: 109.5° TETRAHEDRAL tetrahedral electron pair geometry 4 electron pairs Put on the H-atoms…….

20. C C There is a better arrangement for four electron pairs: H TETRAHEDRAL 109.5° H H H tetrahedral EPG 4 electron pairs The shape of CH4 is tetrahedral. NOW LOOK AT AMMONIA

21. N There are four electron pairs around the nitrogen atom. NH3 The electron pair geometry around the nitrogen is tetrahedral: H N H H PUT ON THE 3 H ATOMS

22. NH3 The electron pair geometry around the nitrogen is tetrahedral: N H H H N There are four electron pairs around the nitrogen atom. PUT ON THE 3 H ATOMS N H H H The shape of NH3 is trigonal pyramidal.

23. H2O The electron pair geometry around the oxygen is tetrahedral: O There are four electron pairs around the oxygen atom. H O H PUT ON THE 2 H-ATOMS O H H The shape of H2O is V-shaped or bent.

26. VALENCE BOND THEORY A covalent bond is formed by an overlap of two valence atomic orbitals that share an electron pair. The better the overlap the stronger the bond The orbitals need to point along the bonds Lets look at methane

27. H C H H H METHANE: a tetrahedral molecule CH4 What orbitals are used? Hydrogen atoms bond using their 1s orbitals. Carbon needs four orbitals to bond with. [He] 2s22p2 Try 2s, 2px , 2py and 2pz

28. . . . C . The electronic configuration of carbon is: [He] 2s22p2 [He] The orbital diagram is: The Lewis dot structure is Promote one of the 2s electrons

29. C PROMOTE AN ELECTRON [He] [He] [He] 2s22p2 [He] 2s12p3 excited state The Lewis dot structure is still Four unpaired electrons We can use these to form chemical bonds

31. A covalent bond is formed by an overlap of two valence atomic orbitals that share an electron pair. Bonds formed with s orbitals will be different to bonds formed with p orbitals. Experiment shows that all four bonds are identical. The three p orbitals are mutually perpendicular, suggesting 90° bond angles. Experiment shows that methane has 109.5° bond angles. We get round this by combining the orbitals

32. H We remember that orbitals are just algebraic functions and so we can combine them C H H H We need four orbitals pointing to the vertices of a tetrahedron…. Combining orbitals is called HYBRIDIZATION

34. 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.

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

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

37. 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

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

39. 2s- 2p + We get two equivalent sporbitals ORIENTED AT 1800

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