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chapter2 - 2. Polar Covalent Bonds: Acids and Bases Based...

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2. Polar Covalent Bonds: Acids and Bases Based on McMurry’s Organic Chemistry , 7 th edition
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2 Quiz 1 (Chapter 1) Results 47 1 24 4 13 3 4 3 8 4 7 3 1 2 0 5 10 15 20 25 30 35 40 45 50 20 19 18 17 16 15 14 13 12 11 10 9 8 7 Quiz Score No. of Students 89 Students 35 Students These Students Need to See Me for Help
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3 Why this chapter? Description of basic ways chemists account for chemical reactivity. Establish foundation for understanding specific reactions discussed in subsequent chapters.
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4 2.1 Polar Covalent Bonds: Electronegativity Covalent bonds can have ionic character These are polar covalent bonds Bonding electrons attracted more strongly by one atom than by the other Electron distribution between atoms is not symmetrical Which elements almost always form ionic bonds?
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5 Bond Polarity and Electronegativity Electronegativity (EN): intrinsic ability of an atom to attract the shared electrons in a covalent bond Differences in EN produce bond polarity Arbitrary scale. As shown in Figure 2.2, electronegativities are based on an arbitrary scale F is most electronegative (EN = 4.0), Cs is least (EN = 0.7) Metals on left side of periodic table attract electrons weakly, lower EN Halogens and other reactive nonmetals on right side of periodic table attract electrons strongly, higher electronegativities EN of C = 2.5
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6 The Periodic Table and Electronegativity Polar Covalent Bond has EN < 2 Ionic Bond has EN > 2 In which direction is the dipole for the following bonds? C-N C-F B-H C-O C-Cl C-H C-C C-Br N-H C-B C-S O-H Electronegativity is responsible for direct stabilization of intermediates and products and their Indirect stabilization via the inductive effect. 3 3 - + 3 3 - + What would be some examples of an ionic bond?
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7 Bond Polarity and Inductive Effect Nonpolar Covalent Bonds : atoms with similar EN Polar Covalent Bonds : Difference in EN of atoms < 2 Ionic Bonds: Difference in EN > 2 C–H bonds, relatively nonpolar C-O, C-X bonds ( more electronegative elements) are polar Bonding electrons toward electronegative atom C acquires partial positive charge, δ + Electronegative atom acquires partial negative charge, δ - Inductive effect: shifting of electrons in a bond in response to EN of nearby atoms
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8 Electrostatic Potential Maps Electrostatic potential maps show calculated charge distributions Colors indicate electron- rich (red) and electron- poor (blue) regions Arrows indicate direction of bond polarity
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9 2.2 Polar Covalent Bonds: Dipole Moments Molecules as a whole are often polar from vector summation of individual bond polarities and lone-pair contributions Strongly polar substances soluble in polar solvents like water; nonpolar substances are insoluble in water. Dipole moment (
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This note was uploaded on 04/07/2008 for the course CHGN 222 taught by Professor Cowley during the Spring '08 term at Mines.

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chapter2 - 2. Polar Covalent Bonds: Acids and Bases Based...

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