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211 LSW Sp07 Exam 1 Organic Chemistry involves mostly CHNOPS and the halogens. Organic compounds use valence shell electrons to bond. Usually only in the s and p orbitals. Orbital Shapes Carbon: z z y x 1s n=1 l=0 ml=0 z y x 2s n=2 l=0 ml=0 z y x 2pz n=2 l=1 z y x 2px n=2 l=1 x 2py n=2 l=1 ml = 1,0,-1 arbitrary assignment Electron configuration Carbon: Full Short form Orbital energy diagram Orbital energy levels diagram 1 y 211 LSW Sp07 Exam 1 Bonding: • Octet of electrons: • Ionic bonds: • Covalent bonds: Example: [CH3COO] • Non-polar bond: • Polar bond: Examples: _ Br2 Na + HCl CO Formal Charges: • The charge on atoms within a neutral (or charged) molecule • Always label the formal charges on any atoms. • The location of formal charges often controls reactivity. • Equations: Bonds C N O F • Recognition: 2 lone pairs 211 LSW Sp07 Exam 1 Lewis Structures: For NO3-: 1. Determine the total number of valence electrons in a molecule 2. Draw a skeleton. a. Connects all atoms b. Use only single bonds. c. In simple molecules, the atom with the most available sites for bonding is usually placed central. d. Determine the number of bonding sites using the number of valence electrons and the ability of an atom to expand its octet. 3. Place the remaining electrons to fill the octets of as many atoms as possible a. Place the electrons on the most electronegative atoms first b. Then proceed to the more electropositive atoms. 4. Fill any unfilled octets by making multiple bonds 5. Indicate the FORMAL CHARGES on all the atoms (keep them as low as possible) O N O 6. Expanded octets occur only in atoms with n=3 (period) or greater. 3 211 LSW Sp07 Exam 1 Molecular Shape: VSEPR Electronic geometries: Molecular geometries: Electronic Geometry Examples Molecular Geometries Linear BeH2 Linear Trigonal planar BF3 Trigonal planar SO2 Bent CH4 Tetrahedral NH3 Trigonal pyramidal H2S Bent PF5 Trigonal bipyramidal TeCl4 See-saw BrF3 T-shaped XeF2 Linear SF6 Octahedral IF5 Square pyramidal XeF4 Square planar Tetrahedral Trigonal bipyramidal Octahedral 4 211 LSW Sp07 Exam 1 Rules for drawing molecules (3D) on paper (2D): 1. 2. 3. 4. Place the largest number of atoms possible in the plane of the paper. Unbroken lines Hashed wedges Solid wedges H Butane C4H10 H H C H H C H C H C H H H H Ammonia NH3 H N H H H Methoxyethane C3H8O (Ethyl methyl ether) H N H H H C O H C H - You try CH3CO2 : 5 C H H H 211 LSW Sp07 Exam 1 Molecular polarity: You should be able to indicate a molecule's polarity. Resonance structures: Resonance hybrid: LEWIS STRUCTURES O O O C C C O O O O O O RESONANCE HYBRID O C O O Rules to remember when considering resonance: • The bonding framework of a molecule remains intact. • You can only move electrons in multiple bonds or lone pairs. • The overall charge of the system remains the same. Electron flow: Curved arrows: indicate the movement of electrons not atoms, the electrons move towards an electron deficient centers (+) 6 211 LSW Sp07 Exam 1 Ranking the importance of resonance structures: A) Satisfies the octet rule. 1) No charge separation are favored over 2) Charge separation as predicted by electronegtivity 3) Charge separation against that predicted by electronegativity. B) Does not satisfies the octet rule. Resonance structures for acetone: O CH3 O CH3 I CH3 O CH3 CH3 O CH3 CH3 II III What is the resonance hybrid of acetone? What is the molecular polarity of acetone? - O CH3 The enolate ion: [CH3CH-C(O)-CH3] (but-3-ene-2-olate) Aromatic ring systems: p-methylaniline (CH3-Φ-NH2) 7 CH3 CH3 211 LSW Sp07 Exam 1 Hybridization: Sigma, σ, overlap: Pi, π, overlap: Bond type Overlaps single σ double σ and π triple σ and two π VSEPR prediction is different from this prediction for CH4 Hybridization: 'hybrid' orbitals: Name of hybrid: 8 211 LSW Sp07 Exam 1 You Try CO: Name: Lewis structure: Predicted Shape: Formal Charge on C: Electronic Configuration: C1- E And for Oxygen: O1+ E 9 211 LSW Sp07 Exam 1 Y X CO C O Π BONDING Y Y 2p C C 2sp C Z X C σ O X O O O Z Z BONDING Draw the σ and π bonding for ethene, CH2CH2, and ethyne, CHCH. ETHENE H H C H C H H H C C H H Π BONDING σ BONDING ETHYNE H C C H H σ BONDING C C Π BONDING 10 H 211 LSW Sp07 Exam 1 Acids and Bases: Same chemical reaction happen simultaneously but looking at it from oppositely. The base, B, removes a proton from the acid, H-A: B +H A Acids Bases Arrenhius BronstedLowry Lewis Acidity Acid ionization: H A Ka Ka = pKa = - log10Ka • The more stable the conjugate base, A-, is then the more the equilibrium favors the product side (Ka > 1) • The more the equilibrium favors products, the more H+ is present. • The more H+ there is then the stronger H-A is as an acid. • The larger Ka implies more dissociation of HA and so the stronger the acid. • The larger Ka is, the more negative the pKa so the lower the pKa, the stronger the acid. 11 211 LSW Sp07 Exam 1 Major factors that affect the stability of the conjugate base, A-. Electronegativity. In the same row of periodic table: HF H2O NH3 CH4 Size. In the same group of periodic table: HI HBr HCl HF Resonance. On the same atom: RCO2H ROH General acidity trend of common organic acids OH O R OH R NH2 R H OH R CLASS pKa Basicity Major factors that affect electron pair availability in a base, B CH3- > NH2- > HO- > F- Electronegativity. in the same row of periodic table: F- > Cl- > Br- > I- Size. in the same group of periodic table: RO- > RCO2- Resonance. On the same atom: General acidity trend of some common organic bases: R NH CLASS NH2 R O OH pKa 12 R NH2