1 Chapter 4 Compounds and Their Bonds 4.8 Attractive Forces in Compounds Copyright © 2009 by Pearson Education, Inc. °

2 Ionic Bonds In ionic compounds, ionic bonds are strong attractive forces. hold positive and negative ions together. Copyright © 2009 by Pearson Education, Inc.

Dipole-Dipole Attractions 3 In covalent compounds, polar molecules exert attractive forces called dipole-dipole attractions. form strong dipole attractions called hydrogen bonds between hydrogen atoms bonded to F, O, or N, and other very electronegative atoms.

4 Dispersion Forces Dispersion forces are weak attractions between nonpolar molecules. caused by temporary dipoles that develop when electrons are not distributed equally.

5 Attractive Forces

6 Melting Points and Attractive Forces Ionic compounds require large amounts of energy to break apart ionic bonds. Thus, they have high melting points. Hydrogen bonds are the strongest type of dipole-dipole attractions. They require more energy to break than other dipole-dipole attractions. Dispersion forces are weak interactions and very little energy is needed to change state.

Melting Points of Some Substances 7

8 Learning Check Identify the main type of attractive forces for each: 1) ionic 2) dipole-dipole 3) hydrogen bonds 4) dispersion A. NCl 3 B. H 2 O C. Br-Br D. KCl E. NH 3

9 Solution Identify the main type of attractive forces for each: 1) ionic 2) dipole-dipole 3) hydrogen bonds4) dispersion 2 A. NCl 3 3 B. H 2 O 4 C. Br-Br 1 D. KCl 3 E. NH 3