CHEMISTRY 161 Chapter 11

1. CHEMISTRY 161 Chapter 11

2. OUTLINE • Solids, Liquids, Gases – Molecular Comparison • 2. Intermolecular Forces • 3. Phase Transitions and Phase Diagrams • 4. Crystalline Solids

3. 1. SOLIDS, LIQUIDS, GASES expand/contract to fill container P V = n R T retain volume and shape retain volume but not the shape microscopic level molecular interactions

4. OUTLINE • Solids, Liquids, Gases – Molecular Comparison • 2. Intermolecular Forces • 3. Phase Transitions and Phase Diagrams • 4. Crystalline Solids

5. 2. INTERMOLECULAR FORCES intermolecular forces - attractions between molecules intramolecular forces - chemical bonds in molecule control physical properties of a substance intra forces STRONGER then inter forces

6. INTERMOLECULAR FORCES • dispersion forces • (London, van der Waals) • 2. dipole – dipole forces • 3. hydrogen bonding • 4. ion-dipole forces strength increases

7. C LONDON FORCES • weak attractions between non-polar atoms or molecules H He H H H

8. LONDON FORCES He He

9. LONDON FORCES induced dipole F ~ 1/d6

10. LONDON FORCES • Polarizability • 2. Numbers of Atoms • 3. Molecular Shape

11. LONDON FORCES - Polarizibility measure how easily the electron cloud on a particle can be distorted increases as volume increases large forces takes more energy to disrupt forces reflected in boiling points

12. LONDON FORCES - Polarizibility

13. LONDON FORCES – Numbers of Atoms boiling point of hydrocarbons demonstrates this

14. LONDON FORCES – Molecular Shape • compact molecules have lower London forces than longer chain-like molecules • H atoms in the more compact neopentane cannot interact as well • with neighboring molecules as the H atoms in the chain n-pentane

15. INTERMOLECULAR FORCES • dispersion forces • (London, van der Waals) • 2. dipole – dipole forces • 3. hydrogen bonding • 4. ion-dipole forces strength increases

16. DIPOLE-DIPOLE FORCES permanent dipole (polar) F ~ 1/d3 (about 1 % of covalent bond)

17. DIPOLE-DIPOLE FORCES permanent dipole (polar) F ~ 1/d3 (about 1 % of covalent bond)

18. or Choose the Substance in Each Pair with the Highest Boiling Point CH2FCH2F CH3CHF2

19. INTERMOLECULAR FORCES • dispersion forces • (London, van der Waals) • 2. dipole – dipole forces • 3. hydrogen bonding • 4. ion-dipole forces strength increases

20. HYDROGEN BONDING • very strong dipole-dipole attraction that occur when • H is covalently bonded to a small, highly electronegative • atom (F, O, or N) (about 10 times stronger than other dipole – dipole interactions) • responsible for the expansion of water as it freezes

21. HYDROGEN BONDING

22. Choose the substance in each pair that is a liquid at room temperature (the other is a gas) CH3OH CH3CHF2 CH3-O-CH2CH3 CH3CH2CH2NH2

23. INTERMOLECULAR FORCES • dispersion forces • (London, van der Waals) • 2. dipole – dipole forces • 3. hydrogen bonding • 4. ion-dipole forces strength increases

24. ION –DIPOLE FORCES solvation

25. ION –DIPOLE FORCES Ion-dipole attractions hold water molecules in a hydrate. Water molecules are found at the vertices of an octahedron around the aluminum ion in AlCl3·6H2O.

26. INTERMOLECULAR FORCES • dispersion forces • (London, van der Waals) • 2. dipole – dipole forces • 3. hydrogen bonding • 4. ion-dipole forces (< 1 % of covalent bond) (1 - 5 % of covalent bond) (5 -10 % of covalent bond) (can be similar to covalent bond)

27. INTERMOLECULAR FORCES

28. APPLICATIONS solubility depends on the attractive forces of solute and solvent molecules polar substance dissolve in polar solvents hydrophilic groups= OH, C=O, COOH, NH2 nonpolar molecules dissolve in nonpolar solvents hydrophobic groups = C-H, C-C Molecules can have both hydrophilic and hydrophobic parts - solubility becomes competition between parts

29. Immiscible Liquids

30. Choose the substance in each pair that is more soluble in water CH3OH CH3CHF2 CH3CH2CH2CH3 CH3Cl

31. OUTLINE • Solids, Liquids, Gases – Molecular Comparison • 2. Intermolecular Forces • 3. Phase Transitions and Phase Diagrams • 4. Crystalline Solids

32. 3. PHASE TRANSITIONS AND PHASE DIAGRAMS evaporation melting sublimation

33. 3. PHASE TRANSITIONS AND PHASE DIAGRAMS evaporation at the molecular level

34. 3. PHASE TRANSITIONS AND PHASE DIAGRAMS liquids with different interaction energies stronger weaker interaction evaporation faster slower

35. vapor pressure • the liquid begins to evaporate in a closed container • dynamic equilibrium is reached when the rate of evaporation and condensation are equal.

36. similar equilibria are reached in melting and sublimation evaporation melting sublimation

37. Measuring the (equilibrium) vapor pressure of a liquid

39. Variation of vapor pressure with temperature. Ether is said to be volatile because it has a high vapor pressure near room temperature

40. The boiling point of a liquid can be defined as the temperature at which the vapor pressure of the liquid is equal to the prevailing atmospheric pressure The normal boiling point is the temperature at which the vapor pressure is 1 atm Molecules with higher intermolecular forces have higher boiling points

41. Boiling points of the hydrogen compounds of elements of Groups IV, V, VI, and VII. Boiling points of molecules with hydrogen bonding are higher that expected.

42. HEATING AND COOLING CURVES (a) A heating curve observed when heat is added at a constant rate. (b) A cooling curve observed when heat is removed at a constant rate. The “flat” regions of the curves identify the melting and boiling points. Supercooling is seen hear as the temperature of the liquid dips below its freezing point.

43. Heating Curve of a Liquid as you heat a liquid, its temperature increases linearly until it reaches the boiling point • Q = mass xCsxDT once the temperature reaches the boiling point, all the added heat goes into boiling the liquid – the temperature stays constant once all the liquid has been turned into gas, the temperature can again start to rise

44. CLAUSIUS-CLAPEYRON • the logarithm of the vapor pressure vs. • inverse absolute temperature is a linear function • the slope of the line x 8.314 J/mol∙K = DHvap • in J/mol • the graph of vapor pressure vs. temperature is an exponential growth curve

45. PHASE DIAGRAM - WATER The line AB is the vapor pressure curve for ice; BD the vapor pressure curve for liquid water; BC the melting point line; point B the triple point (the temperature where all three phases are in equilibrium); and point D labels the critical point (critical temperature and pressure). Above the critical temperature a distinct liquid phase does not exist, regardless of pressure.

46. PHASE DIAGRAM – CARBON DIOXIDE

47. OUTLINE • Solids, Liquids, Gases – Molecular Comparison • 2. Intermolecular Forces • 3. Phase Transitions and Phase Diagrams • 4. Crystalline Solids

48. 4. CRYSTALLINE SOLIDS CRYSTAL

49. CHRYSTAL STRUCTURES crystalline solids have a very regular arrangement x-ray diffraction a crystal is struck by x-rays, which are reflected the wavelength is adjusted to result in an interference pattern – at which point the wavelength is an integral multiple of the distances between the particles

50. X RAY CHRISTALLOGRAPHY X-ray Crystallography