1 Chapter 10 Molecular Structure: Liquids and Solids 10.4 Electronegativity and Polarity Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 Electronegativity values Indicate the attraction of an atom for shared electrons. Increases 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 Low values High values Electronegativity increases Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

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 nonmetal 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 © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

7 Ionic Bonds An ionic bond Occurs between metal and nonmetal ions. Is a result of electron transfer. Has a large electronegativity difference (1.8 or more). Examples: Atoms Electronegativity Type 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 Predicting Bond Types Table 10.4 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

9 Range of Bond Types Table 10.5 Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

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 H — N —H dipole │ H 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. HBr 1) linear; one polar bond (dipole); polar C. Br 2 2) linear; nonpolar bond; nonpolar D. SiBr 4 2) tetrahedral; dipoles cancel; nonpolar