Basic Chemistry Copyright © 2011 Pearson Education, Inc. 1 Chapter 10 Structures of Solids and Liquids 10.4 Attractive Forces between Particles

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 2 Ionic Bonds In ionic compounds, ionic bonds are strong attractive forces hold positive and negative ions together

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 3 Dipole-Dipole Attractions 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 atoms that are strongly electronegative

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 4 Dipole-Dipole Attractions

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 5 Dispersion Forces Dispersion forces are weak attractions between nonpolar molecules caused by temporary dipoles that develop when electrons are not distributed equally

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 6 Comparison of Bonding and Attractive Forces

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Mass and Boiling Points Nonpolar covalent compounds such as alkanes have higher boiling points as the mass of the compounds increases more dispersion forces form 7

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 8 Melting Points and Attractive Forces Ionic bonds require large amounts of energy to break apart. Ionic compounds have very high melting points. Hydrogen bonds are the strongest type of dipole- dipole attractions. They require more energy to break than other dipole attractions. Compounds with hydrogen bonds have moderate melting points.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 9 Melting Points and Attractive Forces (continued) Dipole-dipole attractions are weaker than hydrogen bonds, but stronger than dispersion forces. They have low to moderate melting points. Dispersion forces are weak and little energy is needed to break them. Compounds with dispersion forces have the lowest melting points.

Basic Chemistry Copyright © 2011 Pearson Education, Inc. Melting Points 10

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 11 Learning Check Identify the major type of attractive force in each of the following substances: 1) ionic bonds 2) dipole-dipole attractions 3) hydrogen bonds 4) dispersion forces A. NCl 3 B. H 2 O C. Br 2 D. KCl E. NH 3

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 12 Solution Identify the major type of attractive force in each of the following substances: 1) ionic bonds 2) dipole-dipole attractions 3) hydrogen bonds 4) dispersion forces 2 A. NCl 3 3 B. H 2 O 4 C. Br 2 1 D. KCl 3 E. NH 3

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 13 Learning Check Identify the compound in each pair that has the higher melting point. Explain. A. NCl 3 or NH 3 B. HBr or Br 2 C. KCl or HCl

Basic Chemistry Copyright © 2011 Pearson Education, Inc. 14 Solution A. NH 3 would have a higher melting point than NCl 3 because the hydrogen bonds in NH 3 are stronger than the dipole-dipole attractions in NCl 3. B. HBr would have a higher melting point than Br 2 because the dipole-dipole attractions in HBr are stronger than the dispersion forces in Br 2 C. KCl would have a higher melting point than HCl because the ionic bonds in KCl are stronger than the dipole-dipole attractions in HCl.