Chapter 10 Structures of Solids and Liquids

1. Chapter 10 Structures of Solids and Liquids 10.4 Attractive Forces between Particles

2. Ionic Bonds In ionic compounds, ionic bonds • are strong attractive forces • hold positive and negative ions together

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

4. Dipole-Dipole Attractions

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

6. Comparison of Bonding and Attractive Forces

7. 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

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.

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.

10. Melting Points

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. NCl3 B. H2O C. Br2 D. KCl E. NH3

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. NCl3 3 B. H2O 4 C. Br2 1 D. KCl 3 E. NH3

13. Learning Check Identify the compound in each pair that has the higher melting point. Explain. A. NCl3 or NH3 B. HBr or Br2 C. KCl or HCl

14. Solution A. NH3 would have a higher melting point than NCl3 because the hydrogen bonds in NH3 are stronger than the dipole-dipole attractions in NCl3. B. HBrwould have a higher melting point than Br2 because the dipole-dipole attractions in HBr are stronger than the dispersion forces in Br2 C. KClwould have a higher melting point than HCl because the ionic bonds in KCl are stronger than the dipole-dipole attractions in HCl.