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

Electronegativity the attraction of an atom for electronsYSU

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

Important Electronegativity Values H 2.1 LiBeBCNOF Cl 3.0 Br 2.8 I 2.5YSU

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

1.3 Lewis Dot Structures of MoleculesYSU

1.4 Double bonds and triple bonds Double bonds - alkenes Triple bonds - alkynesYSU

1.5 Polar covalent bonds and electronegativity H 2 HFH 2 O CH 4 CH 3 Cl Based on electronegativity YSU

1.6 Structural Formula - Shorthand in Organic ChemistryYSU

1.6 Constitutional Isomers Same molecular formula, completely different chemical and physical properties YSU

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

1.8 Resonance Structures - Electron Delocalization Table 1.6 – formal rules for resonanceYSU

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

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

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Trigonal planar geometry of bonds to carbon in H 2 C=O Linear geometry of carbon dioxide YSU

1.10 Molecular dipole momentsYSU Figure 1.7

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

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

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

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

Proton Transfer from HBr to Water YSU

Equilibrium Constant for Proton Transfer YSU

Acids and Bases: Arrow PushingYSU

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Need to know by next class: pKa = -log 10 Ka STRONG ACID = LOW pKa WEAK ACID = HIGH pKa HI, HCl, HNO 3, H 3 PO 4 pKa -10 to -5 Super strong acids H 3 O + pKa – 1.7 RCO 2 HpKa ~ 5acids PhOHpKa ~ 10get H 2 O, ROHpKa ~ 16weaker RCCH (alkynes)pKa ~ 26 RNH 2 pKa ~ 36Extremely weak acid RCH 3 pKa ~ 60Not acidic at allYSU

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

1.15 How Structure Affects Acid/Base Strength 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. HFHClHBr HI pKapKapKapKa weakest acid strongest acid strongest H—X bond weakest H—X bondYSU

Electronegativity Acidity increases across periodic table as the atom attached to H gets more electronegative (HF>H 2 O>H 2 N>CH 4 ). pKapKapKapKa weakest acid strongest acid least electronegative most electronegative CH 4 NH 3 H2OH2OH2OH2O HFYSU

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 CF 3 CH 2 OH is more polarized CF 3 CH 2 O- is stabilized by EW fluorine atomsYSU

Resonance Stabilization in Anion Delocalization of charge in anion (resonance) makes the anion more stable and thus the conjugate acid more acidic e.g. (CH 3 CO 2 H > CH 3 CH 2 OH). pKa ~16 pKa ~5YSU

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

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, BF 3 is a gas and CH 3 CH 2 OCH 2 CH 3 has a boiling point of 34°C.YSU