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1.3 Covalent Bonding - Electrons Shared

1.2-1.3 Bonding. Atoms trying to attain the stable configuration of a noble (inert) gas - often referred to as the octet rule. 1.2 Ionic Bonding - Electrons Transferred. 1.3 Covalent Bonding - Electrons Shared. type of bond that is formed is dictated by the

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1.3 Covalent Bonding - Electrons Shared

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  1. 1.2-1.3 Bonding Atoms trying to attain the stable configuration of a noble (inert) gas - often referred to as the octet rule 1.2 Ionic Bonding -Electrons Transferred 1.3 Covalent Bonding -Electrons Shared type of bond that is formed is dictated by the relativeelectronegativitiesof the elements involved YSU

  2. Electronegativity YSU the attraction of an atom for electrons

  3. 1.2 Ionic bonding Electrons Transferred Big differences in E.N. values Metals reacting with non-metals YSU

  4. Important Electronegativity Values YSU H 2.1 LiBe B C N O F 1.0 2.0 2.5 3.0 3.5 4.0 Cl 3.0 Br 2.8 I 2.5

  5. 1.3 Covalent Bonding - Similar electronegativities H . + H . H : H Hydrogen atoms Hydrogen molecule B.D.E +104 kcal/mol B.D.E +104 kcal/mol B.D.E. = bond dissociation energy YSU

  6. 1.3 Lewis Dot Structures of Molecules YSU

  7. 1.4 Double bonds and triple bonds YSU Double bonds - alkenes Triple bonds - alkynes

  8. 1.5 Polar covalent bonds and electronegativity H2 HF H2O CH4 CH3Cl Based on electronegativity YSU

  9. 1.6 Structural Formula - Shorthand in Organic Chemistry YSU

  10. 1.6 ConstitutionalIsomers Same molecular formula, completely different chemical and physical properties YSU

  11. 1.7 Formal Charge Formal charge = group number - number of bonds - number of unshared electrons YSU

  12. 1.8 Resonance Structures - Electron Delocalization Table 1.6 – formal rules for resonance YSU

  13. 1.9 Shapes of Molecules Shapes of molecules are predicted using VSEPR theory YSU

  14. 1.9 Shape of a molecule in terms of its atoms Figure 1.9 Table 1.7 – VSEPR and molecular geometry YSU

  15. YSU

  16. Trigonal planar geometry of bonds to carbon in H2C=O Linear geometry of carbon dioxide YSU

  17. 1.10 Molecular dipole moments Figure 1.7 YSU

  18. 1.11 Curved Arrows – Extremely Important • Curved arrows used to track flow of electrons in chemical reactions. • Consider reaction shown below which shows the dissociation of AB: YSU

  19. Curved Arrows to Describe a Reaction Many reactions involve both bond breaking and bond formation. More than one arrow may be required. YSU

  20. 1.12 Acids and Bases - Definitions Arrhenius An acid ionizes in water to give protons. A base ionizes in water to give hydroxide ions. Brønsted-Lowry An acid is a proton donor. A base is a proton acceptor. Lewis An acid is an electron pair acceptor. A base is an electron pair donor. YSU

  21. 1.13 A Brønsted-Lowry Acid-Base Reaction A proton is transferred from the acid to the base. – + B : H A B : A + + H Base acid conjugate acid conjugate base YSU

  22. Proton Transfer from HBr to Water YSU

  23. Equilibrium Constant for Proton Transfer YSU

  24. Acids and Bases: Arrow Pushing YSU

  25. YSU

  26. YSU

  27. YSU Need to know by next class: pKa = -log10Ka STRONG ACID = LOW pKa WEAK ACID = HIGH pKa HI, HCl, HNO3, H3PO4pKa -10 to -5 Super strong acids H3O+pKa – 1.7 RCO2H pKa ~ 5 acids PhOH pKa ~ 10 get H2O, ROH pKa ~ 16 weaker RCCH (alkynes) pKa ~ 26 RNH2 pKa ~ 36 Extremely weak acid RCH3 pKa ~ 60 Not acidic at all

  28. 1.14 What happened to pKb? • A separate “basicity constant” Kb is not necessary. • Because of the conjugate relationships in the Brønsted-Lowry approach, we can examine acid-base reactions by relying exclusively on pKa values. pKa ~60 Essentially not acidic Corresponding base Extremely strong YSU

  29. 1.15 How Structure Affects Acid/Base Strength YSU HF HCl HBr HI 3.1 -3.9 -5.8 -10.4 pKa weakest acid strongest acid strongest H—X bond weakest H—X bond • Bond Strength • Acidity of HX increases (HI>HBr>HCl>HF) down the periodic table as H-X bond strength decreases and conjugate base (X:- anion) size increases.

  30. Electronegativity Acidity increases across periodic table as the atom attached to H gets more electronegative (HF>H2O>H2N>CH4). YSU HF CH4 NH3 H2O 60 36 16 3.1 pKa weakest acid strongest acid least electronegative most electronegative

  31. YSU Inductive Effects Electronegative groups/atoms remote from the acidic H can effect the pKa of the acid. pKa = 16 pKa = 11.3 • O – H bond in CF3CH2OH is more polarized • CF3CH2O- is stabilized by EW fluorine atoms

  32. YSU Resonance Stabilization in Anion Delocalization of charge in anion (resonance) makes the anion more stable and thus the conjugate acid more acidic e.g. (CH3CO2H > CH3CH2OH). pKa ~16 pKa ~5

  33. 1.16 Acid-base reactions - equilibria YSU The equilibrium will lie to the side of the weaker conjugate base

  34. YSU 1.17 Lewis acids and Lewis bases Product is a stable substance. It is a liquid with a boiling point of 126°C. Of the two reactants, BF3 is a gas and CH3CH2OCH2CH3 has a boiling point of 34°C.

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