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lecture 1.1 - Electronegativity Electronegativity a measure...

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1- 1-1 Electronegativity Electronegativity Electronegativity: Electronegativity: a measure of an atom’s attraction for the electrons it shares with another atom in a chemical bond Pauling scale Pauling scale generally increases left to right in a row generally increases bottom to top in a column
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1- 1-2 Covalent Bonds Covalent Bonds The simplest covalent bond is that in H 2 the single electrons from each atom combine to form an electron pair the shared pair functions in two ways simultaneously; it is shared by the two atoms and fills the valence shell of each atom The number of shared pairs one shared pair forms a single bond two shared pairs form a double bond three shared pairs form a triple bond H H H-H + ∆Η 0 = -435 κϑ(-104 κχαλ 29 /μ ολ
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1- 1-3 Polar and Nonpolar Covalent Bonds Polar and Nonpolar Covalent Bonds Although all covalent bonds involve sharing of electrons, they differ widely in the degree of sharing We divide covalent bonds into nonpolar covalent bonds polar covalent bonds Difference in  Electronegativity Between Bonded Atoms Type of Bond Less than 0.5 0.5 to 1.9 Greater than 1.9 Nonpolar covalent Polar covalent Ions form
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1- 1-4 Polar and Nonpolar Covalent Bonds Polar and Nonpolar Covalent Bonds an example of a polar covalent bond is that of H-Cl the difference in electronegativity between Cl and H is 3.0 - 2.1 = 0.9 we show polarity by using the symbols δ δ + and δ δ - , or by using an arrow with the arrowhead pointing toward the negative end and a plus sign on the tail of the arrow at the positive end H Cl δ + d- H Cl
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1- 1-5 Polar Covalent Bonds Polar Covalent Bonds Bond dipole moment ( Bond dipole moment ( μ μ ): ): a measure of the polarity of a covalent bond the product of the charge on either atom of a polar bond times the distance between the nuclei Table 1.7 shows average bond dipole moments of selected covalent bonds H-O H-N H-C H-S C-I C-F C-Cl C-Br C-N - C-O C=N C=O -  Bond  Dipole    (D) Bond 1.4 1.5 1.5 1.4 1.2 Bond  Bond  Dipole    (D) 1.3 0.3 0.7 0.2 0.7 2.3 3.5  Bond  Dipole    (D) Bond
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1- 1-6 Lewis Structures - Table 1.3 Lewis Structures - Table 1.3 In neutral molecules hydrogen has one bond carbon has 4 bonds and no lone pairs nitrogen has 3 bonds and 1 lone pair oxygen has 2 bonds and 2 lone pairs halogens have 1 bond and 3 lone pairs H 2 O (8) NH 3  (8) CH 4  (8) HCl (8) C 2 H 4  (12) C 2 H 2  (10) CH 2 O (12) H 2 CO 3  (24) H-O-H H-N-H H H-C-H H H H-Cl H-C C-H H H C O H H C C H H O O C H H O Ethylene Hydrogen chloride M ethane Ammonia Water Carbonic acid Formaldehyde Acetylene
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1- 1-7 Formal Charge Formal Charge Formal charge: Formal charge: the charge on an atom in a molecule or a polyatomic ion To derive formal charge 1. write a correct Lewis structure for the molecule or ion 2. assign each atom all its unshared (nonbonding) electrons and one-half its shared (bonding) electrons 3. compare this number with the number of
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