Chapter 10 Liquids, Solids, and Phase Change

1. Chapter 10Liquids, Solids, and Phase Change CHM 112 M. Prushan

2. Why Do Solids and Liquids Exist? • Intermolecular Forces gases – Little to no attraction between molecules CHM 112 M. Prushan

3. Why Do Solids and Liquids Exist? • Intermolecular Forces liquids – Fairly strong forces between a few molecules CHM 112 M. Prushan

4. Why Do Solids and Liquids Exist? • Intermolecular Forces solids – Strong forces prevent large amount of motion between molecules/atoms CHM 112 M. Prushan

5. What makes a molecule polar? • Polar molecules are said to possess a permanent dipole moment. • Dipole moment measured in units of Debye (Q x r ) [charge x distance] 1 D = 3.336 x 10-30 coulomb meters Prof. Peter Debye Noble Prize 1936 CHM 112 M. Prushan

6. Dr. Prushan, enough physics, what does it mean? • OK… Let’s go back to Lewis Structures and VSEPR • Examples: Draw Lewis Structures and Predict the Geometry of : NH3, H2O, CH4, CH3Cl,CHCl3 CO2, CCl4 (Yes, there was a reason you needed this) CHM 112 M. Prushan

7. CH4 CH3Cl CHCl3 CCl4 NH3 H2O CO2 Trigonal Pyramidal Bent Linear Examples Tetrahedral CHM 112 M. Prushan

8. NH3 H2O CO2 Trigonal Pyramidal Bent Linear Polar or Not Polar That is the Question? CHM 112 M. Prushan

9. NH3 H2O CO2 Trigonal Pyramidal Bent Linear Polar or Not Polar That is the Question? m = 1.47 D m = 1.85 D m = 0 D d - d - d + d + d - d + d - CHM 112 M. Prushan

10. CH4 CH3Cl CHCl3 CCl4 d - d + d - d + Polar or Not Polar That is the Question? m = 0 D m = 1.87 D m = 1.90 D m = 0 D CHM 112 M. Prushan

11. Types of Intermolecular Forces • 4 main types of intermolecular forces (1) London (Dispersion) Forces (2) Dipole-Dipole Forces (3) Ion-Dipole Forces (4) Hydrogen Bonds Increasing Strength CHM 112 M. Prushan

12. London (Dispersion) Forces Weakest of the IM forces. All molecules have Dispersion forces Result of interactions between instantaneous dipole moments. Prof. Fritz London CHM 112 M. Prushan

13. Dipole-Dipole Forces • Result of permanent dipole moments in polar molecules CHM 112 M. Prushan

14. Ion-Dipole Forces The force which dissolves ionic compounds A result of interactions between ions and solvent molecules CHM 112 M. Prushan

15. Hydrogen Bonds • Strongest of the intermolecular forces • NOT a chemical bond • MUST contain hydrogen covalently bonded to F, Cl, O or N. • Essential for Life! CHM 112 M. Prushan

16. Hydrogen Bonds If the boiling point of CO2 is , and CS2 is Molecules with larger molecular weights have higher boiling points. So why is H2O a liquid, but H2S is a gas? CHM 112 M. Prushan

17. BONDS… Hydrogen Bonds CHM 112 M. Prushan

18. Why are Snow Flakes Hexagons? CHM 112 M. Prushan

19. Hydrogen Bonds and Life • Life Depends of H-bonds • The “Stuff” of Life relies on them to stay together Proteins, Enzymes Nucleic Acids (DNA, RNA) Sugar-phosphate Backbond and Base Pairs Amino Acids CHM 112 M. Prushan

20. Amino acids bond together to make polypeptides The polypeptides fold to make the secondary structure of proteins How and Why does the alpha structure form?? Linus Pauling Discovered How, in 1948 While in bed with a cold…. Lets let him describe how… CHM 112 M. Prushan

21. Now let’s try that… Come on down and get a polypeptide CHM 112 M. Prushan

22. CHM 112 M. Prushan

23. Hydrogen Bonds are also important in DNA CHM 112 M. Prushan

24. Which goes with which ??? A – T G – C Right??? BUT WHY???? Come on down and get some base pairs CHM 112 M. Prushan

25. The Guanine-Cytosine (GC) Base Pair CHM 112 M. Prushan

26. The Guanine-Cytosine (GC) Base Pair CHM 112 M. Prushan

27. Effect of Intermolecular forces on melting and boiling points of molecular covalent substances Why does HF have the highest BP? Molecular wts. 132 20 77 81 32 16 128 37 Molecular wts. BONDS… Hydrogen Bonds Increase only due to increase in MW, Since all are non-polar CHM 112 Summer 2007 M. Prushan