1 Chapter 6 Molecules and Covalent Compounds 6.5 Electronegativity and Bond Polarity 6.6 Polarity of Molecules Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 Electronegativity values: Indicate the attraction of an atom for shared electrons Increase from left to right going across a period on the periodic table Is high for the nonmetals with fluorine as the highest Is low for the metals Electronegativity

3 Some Electronegativity Values for Group A Elements Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Low values High values

4 A nonpolar covalent bond, Occurs between nonmetals Is an equal or almost equal sharing of electrons Has almost no electronegativity difference (0.0 to 0.4) Examples: Atoms Electronegativity Type of Bond Difference N-N = 0.0 Nonpolar covalent Cl-Br = 0.2 Nonpolar covalent H-Si = 0.3 Nonpolar covalent Nonpolar Covalent Bonds

5 A polar covalent bond, Occurs between nonmetals atoms Is an unequal sharing of electrons Has a moderate electronegativity difference (0.5 to 1.7) Examples: Atoms ElectronegativityType of Bond Difference O-Cl = 0.5Polar covalent Cl-C = 0.5Polar covalent O-S = 1.0Polar covalent Polar Covalent Bonds

6 Comparing Nonpolar and Polar Covalent Bonds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

7 Ionic Bonds An ionic bond, Occurs between metal and nonmetals ions Is a results of electron transfer Has a large electronegativity difference (1.8 or more) Examples: Atoms ElectronegativityType of Bond Difference Cl-K 3.0 – 0.8 = 2.2Ionic N-Na 3.0 – 0.9 = 2.1Ionic S-Cs2.5 – 0.7= 1.8Ionic

8 Range of Bond Types

9 Predicting Bond Types

10 Use the electronegativity difference to identify the type of bond between the following as: nonpolar covalent (NP), polar covalent (P), or ionic (I). A. K-N B. N-O C. Cl-Cl D. H-Cl Learning Check

11 Use the electronegativity difference to identify the type of bond between the following as: nonpolar covalent (NP), polar covalent (P), or ionic (I). A. K-N2.2ionic (I) B. N-O0.5 polar covalent (P) C. Cl-Cl0.0nonpolar covalent (NP) D. H-Cl0.9polar covalent (P) Solution

12 Polar Molecules A polar molecule, Contains polar bonds Has a separation of positive and negative charge called a dipole indicated with  + and  Has dipoles that do not cancel  +  - H–Cl Cl — N — Cl dipole Cl dipoles do not cancel

13 Nonpolar Molecules A nonpolar molecule, Contains nonpolar bonds Cl–Cl H–H Or has a symmetrical arrangement of polar bonds O=C=O Cl Cl–C–Cl Cl dipoles cancel

14 Determining Molecular Polarity STEP 1 Write the electron-dot formula. STEP 2 Determine the polarity of the bonds. STEP 3 Determine if any dipoles cancel or not. Example: H 2 O.. H─O : H 2 O is polar │ H dipoles do not cancel

15 Learning Check Identify each of the following molecules as: 1) polar or 2) nonpolar. Explain. A. PBr 3 B. HBr C. Br 2 D. SiBr 4

16 Solution Identify each of the following molecules as: 1) polar or 2) nonpolar. Explain. A. PBr 3 1) pyramidal; dipoles don’t cancel; polar B. HBr1) linear; one polar bond (dipole); polar C. Br 2 2) linear; nonpolar bond; nonpolar D. SiBr 4 2) tetrahedral; dipoles cancel; nonpolar