Barron’s Ch 7 Liquids, Solids, and Phase Change Highlights Part 1

1. Barron’s Ch 7 Liquids, Solids, and Phase ChangeHighlights Part 1

2. Intermolecular Forces [disperson (London), dipole-dipole, hydrogen bonding]-ion-dipoleThey are weaker than Intramolecular Bonds [non-polar covalent, polar covalent, ionic] Liquids—properties [e.g. boiling point] are determined by the type and strength of the Intermolecular Forces within them Atmospheric Pressure and Boiling Point reduced atmospheric pressure means lower boiling points Solids—crystalline, metallic, amorphous e.g.sodium chloride, potassium, glass or plastic Heating Curve of Water temperature changes vs. time as ice is heated to steam Phase Diagrams—show the phases [solid, liquid, gas] of one substance on a graph with pressure and temperature axes.

3. Intermolecular Forces Attractions between molecules are not nearly as strong as the intramolecular attractions that hold compounds together.They are strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities.

4. Intermolecular Forces Forces of attraction between different molecules rather than bonding forces within the same molecule. • Dispersion [London] Forces • Dipole-dipole attraction • Hydrogen bonds Other imfs • Ion-Dipole van der Waals Forces

5. Dispersion [London] Forces • These forces are present in all molecules, whether they are polar or nonpolar. • London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.

6. Factors Affecting London Forces • The strength of dispersion forces tends to increase with increased molecular weight. • Larger atoms have larger electron clouds, which are easier to polarize.

7. Factors Affecting London Forces • The shape of the molecule affects the strength of dispersion forces: long, skinny molecules (like n-pentane tend to have stronger dispersion forces than short, fat ones (like neopentane). • This is due to the increased surface area in n-pentane.

8. Dipole-Dipole Interactions • Molecules that have permanent dipoles are attracted to each other. • The positive end of one is attracted to the negative end of the other and vice-versa. • These forces are only important when the molecules are close to each other.

9. Dipole-Dipole Interactions The more polar the molecule, the higher is its boiling point.

10. Hydrogen Bonding • The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong. • We call these interactions hydrogen bonds.

11. Hydrogen Bonding Hydrogen bonding--from a hydrogen that’s directly attached to a highly electronegative nitrogen, oxygen, OR fluorine interacting with an N, O, or F on another molecule

12. EFFECT of Hydrogen Bonding on Boiling Point of Water • The nonpolar series (SnH4 to CH4) follow the expected trend. • The polar series follows the trend from H2Te through H2S, but water is quite an anomaly.

13. Ion-Dipole Interactions • A fourth type of force, ion-dipole interactions are an important force in solutions of ions. • The strength of these forces are what make it possible for ionic substances to dissolve in polar solvents.

14. Summarizing Intermolecular Forces

15. Effect of Pressure on Boiling Point

16. Crystalline Solids highly regular arrangement of their components [table salt (NaCl), pyrite (FeS2)].

17. Metallic Solids Model: Packing uniform, hard spheres to best use available space. This is called closest packing. Each atom has 12 nearest neighbors.

18. Amorphous solids: • considerable disorder in their structures (glass and plastic).

19. Heating Curve Temperature remains constant during a phase change. Water phase changes

20. Phase Diagram • Represents phases as a function of pressure vs. temperature. • Critical pressure: pressure required to liquefy AT the critical temperature. [y-axis] • Critical temperature: temperature above which the vapor cannot be liquefied.[x-axis] • Critical point: both the critical temperature and pressure (for water, Tc = 374°C and 218 atm). • (y,x)

21. Phase changes by Name

22. Water Water

23. Carbon dioxide Carbon dioxide