General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake 5.7 Electronegativity and Bond Polarity Chapter 5 Compounds and Their Bonds © 2013 Pearson Education, Inc. Lectures

© 2013 Pearson Education, Inc. Chapter 5, Section 7 2 Electronegativity  is a measure of an atom’s ability to attract bonding electrons.  increases from left to right, going across a period on the periodic table.  decreases going down a group on the periodic table.  is high for the nonmetals, with fluorine as the highest.  is low for the metals and transition metals. Electronegativity

© 2013 Pearson Education, Inc. Chapter 5, Section 7 3 Bonding and Electronegativity The difference in the electronegativity of two atoms can be used to predict the type of bond that forms. Bonds are classified as:  nonpolar covalent  polar covalent  ionic

© 2013 Pearson Education, Inc. Chapter 5, Section 7 4 Some Electronegativity Values

© 2013 Pearson Education, Inc. Chapter 5, Section 7 5 A nonpolar covalent bond  occurs between nonmetals.  has 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 Nonpolar Covalent Bonds

© 2013 Pearson Education, Inc. Chapter 5, Section 7 6 A polar covalent bond  occurs between nonmetal atoms that do not share electrons equally.  has a moderate electronegativity difference (0.5 to 1.7). Examples: Atoms ElectronegativityType of Bond Difference Polar Covalent Bonds

© 2013 Pearson Education, Inc. Chapter 5, Section 7 7 Comparing Nonpolar and Polar Covalent Bonds

© 2013 Pearson Education, Inc. Chapter 5, Section 7 8 Bond Polarity and Dipoles Bonds become more polar as the difference in electronegativity values of bonding atoms increases. Polar covalent bonds have a separation of charges called a dipole. The positive and negative ends of the dipole are indicated by the lowercase Greek letter delta with a positive or negative sign, δ+ and δ-, or an arrow that points from the positive to the negative charge.

© 2013 Pearson Education, Inc. Chapter 5, Section 7 9 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

© 2013 Pearson Education, Inc. Chapter 5, Section 7 10 Electronegativity and Bond Types

© 2013 Pearson Education, Inc. Chapter 5, Section 7 11 Predicting Bond Types

© 2013 Pearson Education, Inc. Chapter 5, Section 7 12 Use the electronegativity difference to identify the type of bond between the following atoms as nonpolar covalent (NP), polar covalent (P), or ionic (I). A. K–N B. N–O C. Cl–Cl D. B–Cl Learning Check

© 2013 Pearson Education, Inc. Chapter 5, Section 7 13 Use the electronegativity difference to identify the type of bond between the following atoms 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. B–Cl1.0polar covalent (P) Solution