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CHEM 333

COURSE WEB PAGE. www.chem.sc.edu/faculty/bryson/index.html. today. CHEM 333. Prerequisites: 112. synthesis. Lab: Non-major ’ s lab 331L Major ’ s lab 333L. contact information course information identify a seat complete prerequisite form lecture Recitations (MTW)

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CHEM 333

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  1. COURSE WEB PAGE www.chem.sc.edu/faculty/bryson/index.html today CHEM 333 Prerequisites: 112 synthesis

  2. Lab: Non-major’s lab 331L Major’s lab 333L contact information course information identify a seat complete prerequisite form lecture Recitations (MTW) recitation assignment - “How to study organic” Chapter 1 BASICS Most Powerpoint slides were modified from those prepared by William Tam & Phillis Chang atoms: electronic structure configuration, valence molecules: ionic - covalent bonds, Lewis model, octet rule, formal charge resonance, electron arrows VSEPR, hybridization structural drawings CHEM 333 Chapter 1 synthesis

  3. Chapter 1 Organic Chemistry - the study ofcompounds with carbon as the principal element Natural organic compounds: food, medicine, and energy Unnatural organics: plastics, synthetic rubber, & super glue Why so versatile? Carbon forms strong bonds with itself and other elements 1a Ch. 1 - 8

  4. Compounds combinations of atoms in specific proportions Atomic structure - nucleus containing protons(+)and neutrons(0) - with a surrounding electron(-) cloud Ch. 1 - 9

  5. Z atomic mass Each element is distinguished by its atomic number (Z) Column=group row = period Atomic number= No. of protons &/or electrons

  6. Isotopes All the nuclei of atoms of the same element have the same number of protons (Z) Some have different masses because they have different numbers of neutrons. Called isotopes Examples: 12C 13C 14C (6 protons 6 neutrons) (6 protons 7 neutrons) (6 protons 8 neutrons)

  7. Valence Electrons Electrons in shells of increasing energy at increasing distances from the nucleus valence shell - electrons in outermost shell valencee(-)sused in making chemical bonds The number of valence electrons = the group number periodic table

  8. Carbon group IVA - 4 valence electrons - 4 bonds - tetravalent if 3 bonds on carbon all unstable but examine for charge If 5 bonds on C wrong!

  9. nitrogen is in group VA N - 5 valence e(-)s oxygen is in group VIA O - 6 e(-)s halogens are in group VIIA F, Cl, Br, I all have 7 e(-)s examples Ch. 1 - 12

  10. - loss or gain of valence electrons -share electrons to fill shells or Bonding - Shape Bonding extremes - IONIC or COVALENT ionic bonds ? covalent bonds ? Periodic pdf

  11. Electronegativity: a measure of an atom’s attraction for the electrons it shares with another atom Pauling scale: increases left to right in a row increases bottom to top in a column

  12. greater than 1.9 ionic 0.5 to1.9 polarcovalent Electronegativity Classification of Bonds electronegativity difference ____ bond type H3C-H non-polar covalent Less than 0.5 2.5 - 2.1 Na+-Cl 0.93 3.16

  13. # of e-s in outer shell He 2 Ne 8 Ar 8 Lewis Structures: show e(-)s around & between atoms in molecules/ions use only the valence electrons Objective: gain, lose, or share e(-) to give each atom a noble gas or stable electron configuration, “octet rule” Ch. 1 - 21

  14. Lewis structures 1. Determine number of valence e(-)s in molecule (ion) ion - add/subtract 1 electron for -/+ charge [ e.g. CH3Br and CHN ] 2. Determine an order of attachment 3. Connect atoms with single bonds. Arrange rest of e(-)s in pairs so atoms have complete shells Shared e(-)s can be single, double or triple bonds 4. Pairs of e(-)s - shown as “-“; nonbonding e(-)s as dots 5. Assess charges

  15. Example: CH3Br analyze valence electrons: each atom & total C H Br 4 + 1x 3 + 7 = 14 Ch. 1 - 24

  16. Lewis structures - Formal Charge CH2N2 HN3 HCN HOCN isomers

  17. Formal Charge unshared electrons 1/2 shared electrons - + = Charge on an atom, ion, molecule is formal charge i.e.H3O+, HO- • To assign Formal Charge to a structure: • Assign each atom: all non-bonding e's • half shared e’s • formal total e(-)s • 2. Compare thisnumberto atom’s valence e(-)s(group no.) Gp. No. 1 7

  18. (Table 1.3) be able to calculate formal charges Ch. 1 - 30

  19. Exceptions to the octet rule: Group 3A - B, Al - due to valence, form 3 bonds - stable but reactive 3rd row+ elements - e.g. S - can share more than 8 e’s

  20. Resonance Theory Lewis structure - well-defined arrangement of electrons Some molecules have more than 1 arrangement of e(-)s (occurs with p-orbitals, π bonds, non-bonded electrons) Ch. 1 - 32

  21. Carbonate [CO3]-2 + note electron arrows! Structures 1–3: not identical are good Lewis structures But C–O bonds in CO3-2 are all equal Ch. 1 - 33

  22. Resonance - whenever a molecule (ion) can be represented by 2 or more Lewis structures that differ only in the positions of the electrons: None of the resonance structures or resonance contributors, represent the molecule [ion, CO3(-2)]. The actual molecule (ion) is a hybrid (average) of these structures “resonance hybrid” Ch. 1 - 34

  23. Link structures with Resonance contributing structures - not real resonance hybrid REAL weighted average Ch. 1 - 35

  24. not a proper - why? Resonance: rules and evaluation 1. Move only electrons resonance contributing structures Not a resonance contributing structure hydrogen atom moved 2. Resonance contributing structures are proper Lewis structures Ch. 1 - 36

  25. 3. Charge creation-separation decreases contribution evaluation 1. The more covalent bonds a resonance contributing structure has, the more important 2. Resonance contributors with all octets (i.e., noble gas structure) are more important less contribution Ch. 1 - 37

  26. not a valid structure 4. Negative charge on the more electronegative atom better 5. Number of electron pairs maintained Ch. 1 - 38

  27. Resonance stabilization is large if the resonance structures are equivalent Ch. 1 - 39

  28. 2nd E level or shell 1st E level shell Atomic Orbitals and Electron Configuration Ch. 1 - 40

  29. Predicting electron configuration Aufbau principle Orbitals filled so lowest energy are filled first Pauli exclusion principle A maximum of two electrons of opposite spinsmay be placed in each orbital Hund’s rule Orbitals of equal energy (degenerate orbitals, i.e. 2p orbitals) add 1 electron to each. Then add a second electron of opposite spin to each degenerate orbital Ch. 1 - 42

  30. Pauli & Lewis Hund’s Rule closed shell next level Valence Shell 3 (s) (p) E 2 (s) 1 (s) Li Be B C N O F Ne H He writing electronic configuration Periodic pdf

  31. electronic configuration No. of e's 4 Be ……. 5 B ……… 6 C 1s2 2s2 2p2 7 N etc. 1 H 1s1 3 Li 1s2 2s1 2 He 1s2 Electronic Configuration What is the electronic configuration of OXYGEN? 1s2, 2s2, 2p4 Periodic pdf

  32. 3D picture of molecules Valence Shell Electron Pair Repulsion Model “VSEPR” geometry of a molecule estimated by considering all the electron pairs about an atom electron pairs repel each other: - in shared covalent bonds - in unshared, nonbonding pairs repulsion between nonbonding pairs> bonding pairs Ch. 1 - 48

  33. ammonia 4 groups tetrahedral 4 groups around central atom methane water Ch. 1 - 49

  34. 2 groups - linear 180o 3 groups about boron - trigonal 120o 180o 120o 109o 4 groups around central atom - tetrahedral 109o Ch. 1 - 51

  35. ground state of carbon The Structure of Methane and Ethane: Hybridization sp3 [ sp2 and sp ] Periodic pdf Ch. 1 - 53

  36. 90o Z Z 180o X X Y Y Why Hybridize? Periodic pdf

  37. http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/FG12_05.JPGhttp://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/FG12_05.JPG

  38. Ch. 1 - 61

  39. s H  bond sp3 C H H H 109o sp3hybridization Carbon: tetrahedral with equivalent bonds and bond angles

  40. H H H H H H free rotation ethane

  41. Ch. 1 - 66

  42. Ch. 1 - 67

  43. sp2 hybridized carbon Ethene (Ethylene): sp2 Hybridization Ch. 1 - 64

  44. sp2 1b 1c 1a Ch. 1 - 68

  45. Restricted Rotation and the Double Bond C=C double bond( ) restrict rotation [C-C single bond free rotation] Ch. 1 - 69

  46. Restricted rotation of C=C trans-2-butene cis-2-butene isomers Ch. 1 - 70

  47. Ch. 1 - 72

  48. 180o linear structure sp hybridize carbon Structure of Ethyne (Acetylene): sp Hybridization Ch. 1 - 71

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