1. 1 You Ever Ask??? Why is water usually a liquid and not a gas? Why does liquid water boil at such a high temperature for such a small molecule? Why does ice float on water? Why do snowflakes have 6 sides? Why is I 2 a solid whereas Cl 2 is a gas? Why are NaCl crystals little cubes?

2. 2 Chapter 11: Liquids, Solids and Intermolecular Forces

3. 3 Chapter Objectives Kinetic-Molecular Description of Liquids & Solids Intermolecular (IMF) Attractions & Phase Changes Properties of Liquids –Viscosity, Surface Tension, Capillary Action –Evaporation, Vapor Pressure, –Boiling Points & Distillation, Heat transfer Phase Changes The following will NOT be covered in class Types of crystals Chapter Topics

4. 4 States of Matter List all the differences between –Solids –Liquids –Gases Kinetic Energy?

5. 5 States of Matter (KE of Matter) The fundamental difference between states of matter is the distance between particles. in liquids & solids are strong: Intermolecular attractions in liquids & solids are strong: KE of molecules << IMF

6. 6 States of Matter Because in the solid and liquid states particles are closer together, we refer to them as condensed phases (depends on T and P).

7. 7 The States of Matter The state a substance is in at a particular temperature and pressure depends on two antagonistic entities: –The kinetic energy of the particles –The strength of the attractions between the particles

8. 8 Examples 1.What is the difference between intermolecular forces and intramolecular forces? 2.List all the intermolecular forces you are familiar with. 3.List all the intramolecular forces you are familiar with. 4.Which forces are stronger?

9. 9 Intermolecular Forces The attractions between molecules are not nearly as strong as the intramolecular attractions that hold compounds together. Intermolecular forces are weaker than intramolecular forces ( to break 2 O-H in bonds in water: 930 kJ/mol; to vaporize water: 43 kJ/mol) Responsible for the existence of condensed states (liquids, solids)

10. 10 Intermolecular Forces They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, surface tension, and viscosities (reflect the strength of the bond). INTRAmolecular forces—the forces that holds atoms together o form molecules INTERmolecular forces: the forces between molecules, ions and molecules-ions.

11. 11 Intermolecular Forces These intermolecular forces as a group are referred to as van der Waals forces (electrostatic forces).

12. 12 IMF Problem For each of the molecules below, Determine the geometry of the molecule Determine the polarity of the molecule List the types of intermolecular force which act between pairs of these molecules. (a) CH 4 (b) PF 3 (c) CO 2 (d) HCN, (e) HCOOH (methanoic acid)

13. 13 Types of IMF Ion – Ion Van der Waals Forces Dipole – dipole (for molecules with dipole moments) Dipole – induced dipole Dispersion forces (London) Hydrogen Bond (special case of dipole-dipole (IMF) London Dispersion Forces (induced dipole-dipole) Ion – induced dipole Ion – dipole Total attraction between molecules may depend on more than one type of intermolecular force.

14. 14 Ion – Ion Forces 08M16VD1

15. 15 Ion-Ion Forces Ion-ion forces: electrostatic forces of attraction between __________________ of ionic compounds. Generally very strong → 250 kJ. (not a true intermolecular force) Ionic compounds: metal and nonmetal or polyatomic anions (NH 4 + ) Coulomb’s law & the attraction energy determine: –melting & boiling points of ionic compounds –the solubility of ionic compounds

16. 16 IMF : Ion – Ion Interaction Example: Arrange the following ionic compounds in the expected order of increasing melting and boiling points. NaF, CaO, CaF 2 you do it What important points must you consider?

17. 17 IMF: Ionic Solids Ion-ion interactions –force of attraction between two oppositely charged ions is determined by Coulomb’s law Energy of attraction between two ions is given by: D:\Media\Movies\08M17AN1.MOV

18. 18 Ion-Ion Forces for comparison of magnitude Na + —Cl - in salt These are the strongest forces. Lead to solids with high melting temperatures. NaCl (lattice energy = 788 kJ/mol), mp = 800 o C MgO (lattice energy = 3890 kJ/mol), mp = 2800 o C

19. 19 Covalent Bonding Forces for comparison of magnitude C–H, 413 kJ/mol C=C, 610 kJ/mol C–C, 346 kJ/mol CN, 887 kJ/mol

20. 20 Ion – Dipole Force

21. 21 Ion-Dipole Interactions 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. Na + (g) + 6H 2 O(l)→ [Na(H 2 O) 6 ] + (aq) ΔHrxn = -405 kJ Hydrated Ions?Coordination Number? Hydrated Ions? Coordination Number?

22. 22 Attraction Between Ions and Permanent Dipoles

23. 23 Attraction between ions and dipole depends on ion charge and ion-dipole distance. Measured by ∆H for M n+ + H 2 O → [M(H 2 O) x ] n+ -1922 kJ/mol -405 kJ/mol -263 kJ/mol Attraction Between Ions and Permanent Dipoles

24. 24 Dipole – Dipole Force D:\Media\Movies\13M04AN2.MOV

25. 25 Dipole-Dipole Forces Solid Liquid liquid 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. Note the difference between solid and liquid.

26. 26 Effect of Dipole Moment on BP SubstanceMMDipole moment BP, K C 3 H 8 propane 440.1231 CH 3 OCH 3 dimethyl ether 461.3248 CH 3 CHO Acetyl aldehyde 442.7294 CH 3 CN acetonitrile 413.9355

27. 27 Dipole-Dipole Interactions The more polar the molecule (higher μ), the higher is its boiling point. Basic attraction : electrostatic, Coulomb’s Law Examples: HCl, CO, SO 2, NF 3, etc

28. 28 Dipole-dipole are of the order of 5 to 20 kJ/mol. (KE due to temp at 25 o C about 4 kJ/mol). Cmpds that have these forces (dipole-dipole) are frequently solids and liquids at room temp. The stronger the forces, the ______ the melting and boiling points of the compounds. IMF: Dipole-Dipole

29. 29 Hydrogen Bond: type of dipole-dipole force 13M07AN2

30. 30 Boiling Points of Simple Hydrogen-Containing Compounds The nonpolar series (SnH 4 to CH 4 ) follow the expected trend. The polar series follows the trend from H 2 Te through H 2 S, but water is quite an anomaly. EXPLAIN!

31. 31 Which of these are capable of forming hydrogen bonds among themselves? a)CH 3 OH b)C 2 H 4 c)CH 3 NH 2 d)HCN e)NH 4 + f)KF g)CH 3 COOH Intermolecular Forces: H-bond

32. 32 Hydrogen Bonding The dipole-dipole interactions experienced when H is bonded to N, O, or F (HIGH ELECTRONEGATIVITY) are unusually strong. Hydrogen nucleus is exposed. We call these interactions hydrogen bonds.

33. 33 Hydrogen Bonding

34. 34 H-Bonding Between Methanol and Water H-bond ---- ++++ ----

35. 35 Hydrogen Bonding in H 2 O H-bonding is especially strong (40 kJ/mol) in water because the O—H bond is very polar there are 2 lone pairs on the O atom Accounts for many of water’s (and other molecules such as DNA, proteins) unique properties such as anomalous high BP and high viscosity.

36. 36 Hydrogen Bonding in H 2 O Ice has open lattice-like structure. Ice density is < liquid. And so solid floats on water. Snow flake: www.snowcrystals.com

37. 37 Hydrogen Bonding in H 2 O Ice has open lattice-like structure. Ice density is < liquid and so solid floats on water. One of the VERY few substances where solid is LESS DENSE than the liquid.

38. 38 Hydrogen Bonding H bonds leads to abnormally high boiling point of water. See Screen 13.7 D:\Media\Movies\13M07AN 1.MOV

39. 39 Group VIAGroup VIIAGroup IVAGroup VA H2OH2O100HF20NH 3 -33CH 4 -161 H2SH2S-65HCl-85PH 3 -87SiH 4 -112 H 2 Se-45HBr-69AsH 3 -60GeH 4 -90 H 2 Te-15HI-35SbH 3 -25 Boiling Point of Hydrides in ºC

40. 40 Hydrogen Bonding in Biology H-bonding is especially strong in biological systems — such as proteins and DNA. D:\Media\Movies\09S03AN1.MOV DNA — helical chains of phosphate groups and sugar molecules. Chains are helical because of tetrahedral geometry of P, C, and O. Chains bind to one another by specific hydrogen bonding between pairs of Lewis bases. —adenine with thymine —adenine with thymine —guanine with cytosine —guanine with cytosine

41. 41 Portion of a DNA chain Double helix of DNA

42. 42 Base-Pairing through H-Bonds

43. 43 Induced Dipole –Induced Dipole (London Dispersion Forces)

44. 44 London Dispersion Forces While the electrons in the 1s orbital of helium would repel each other (and, therefore, tend to stay far away from each other), it does happen that they occasionally wind up on the same side of the atom.

45. 45 London Dispersion Forces The helium atom becomes polar, with an excess of electrons on the left side and a shortage on the right side. Instantenous dipole forms (for an instant) Instantaneous dipole

46. 46 London Dispersion Forces Another helium nearby, then, would have a dipole induced in it, as the electrons on the left side of helium atom 2 repel the electrons in the cloud on helium atom 1.

47. 47 London Dispersion Forces London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.

48. 48 London Dispersion Forces These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this way is called POLARIZABILITY.

49. 49 Forces Involving Dipole -Induced Dipole Process of inducing a dipole is polarizationProcess of inducing a dipole is polarization Degree to which electron cloud of an atom or molecule can be distorted in its polarizability.Degree to which electron cloud of an atom or molecule can be distorted in its polarizability.

50. 50 IMF: London Dispersion Forces Induced Dipoles: the temporary separation of positive and negative charges in a neutral particle due to the proximity of an ion, dipole, or another induced dipole. On average μ = 0. London Dispersion Forces: attractive forces (electrostatic in origin) that arise as a result of temporary dipoles induced in atoms or molecules (instantaneous dipoles). Weak: 0.1- 5 kJ/mol Dispersion forces allow non-polar molecules to condense. Exist in all molecules!!!!! Importance depends on the type of intermolecular forces.

51. 51 IMF: London Dispersion Forces London Forces very weak only attractive force in nonpolar molecules Ar atom Cluster of Ar atoms

52. 52 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.

53. 53 Effect of Geometry (shape) on BP of Molecules CompoundMMBP, ºC N-butane58-0.45 Isobutane58-12.0 N-pentane7236.1 2-methyl butane7227.8 2,2 methyl propane729.5 Given the same molecular mass, GEOMETRY is important

54. 54 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 (larger polarizability.

55. 55 Boiling Points of Hydrocarbons Boiling Points of Hydrocarbons CH 4 C2H6C2H6C2H6C2H6 C3H8C3H8C3H8C3H8 C 4 H 10 Molecule MMBP ( o C) CH 4 (methane) 16- 161.5 CH 4 (methane) 16- 161.5 C 2 H 6 (ethane)38- 88.6 C 2 H 6 (ethane)38- 88.6 C 3 H 8 (propane) 44- 42.1 C 3 H 8 (propane) 44- 42.1 C 4 H 10 (butane)58 - 0.5 C 4 H 10 (butane)58 - 0.5 Note: linear relationship between BP and MM (Polarizability increases).

56. 56 Which Have a Greater Effect: Dipole-Dipole Interactions or Dispersion Forces? If two molecules are of comparable size and shape, dipole-dipole interactions will likely be the dominating force. If one molecule is much larger than another, dispersion forces will likely determine its physical properties.

57. 57 Dipole – Induced Dipole

58. 58 FORCES INVOLVING INDUCED DIPOLES How can non-polar molecules such as O 2 and I 2 dissolve in water? The water dipole a dipole in the O 2 electric cloud. The water dipole INDUCES a dipole in the O 2 electric cloud. Dipole-induced dipole

59. 59 Forces Involving Dipole -Induced DIPOLE Solubility increases with mass of the gas

60. 60 Forces Involving Dipole -induced Dipole Consider I 2 dissolving in ethanol, CH 3 CH 2 OH. O H -  +  I-I R -  +  O H +  -  R The alcohol temporarily creates or a dipole in I 2. The alcohol temporarily creates or INDUCES a dipole in I 2.

61. 61 Ion-dipole forces (very strong; solubility of ions in water) Dipole-dipole forces (larger dipole moments)Dipole-dipole forces (larger dipole moments) –Special dipole-dipole force: hydrogen bonds Induced dipoles (occur in all substances; important for nonpolar molecules); increase with molar mass (glues); depend on geometry. For large molecules may exceed the force of dipole-dipole force (polymers, glues)Induced dipoles (occur in all substances; important for nonpolar molecules); increase with molar mass (glues); depend on geometry. For large molecules may exceed the force of dipole-dipole force (polymers, glues) Summary of Intermolecular Forces In general: ionic forces the strongest; then hydrogen bonding; dipole-dipole; and lastly dispersion for species of similar molar mass. London Dispersion Forces exist in all molecules and ions.

62. 62 Summarizing Intermolecular Forces

63. 63 Summary of dipole forces

64. 64 Intermolecular Forces Summary

65. 65 Intermolecular Forces Figure 13.13

66. 66 Example What type of intermolecular forces exist between the following pairs? 1.HBr and H 2 S 2.Cl 2 and CBr 4 3.I 2 and NO 3 - 4.NH 3 and C 6 H 6 1. Dipole-dipole; dispersion; 2. dispersion; 3. ion-induced dipole; dispersion 4. dipole-induced dipole; dispersion

67. 67 Intermolecular Forces: Examples 5. Order the following compounds in order of increasing MP and BP: a)N 2, O 2, H 2 b)Cl 2, F 2, I 2, Br 2 c)SiH 4, GeH 4, SnH 4, CH 4 Order of MP and BP: (a) H 2 < N 2 <O 2 (b) F 2 <Cl 2 <Br 2 <I 2 (c) CH 4 <SiH 4 <GeH 4 <SnH 4 Always compare like species. 6.But what about HF, HCl, HBr, HI 7.and H 2 O, H 2 S, H 2 Se, H 2 Te 8.and NH 3, PH 3, AsH 3 and SbH 3.

68. 68 Examples 1. List the IMF and arrange the substances BaCl 2, H 2, CO, and Ne in order of increasing boiling points. 2. In which of the following substances is hydrogen bonding possible? a.Methane b.Methyl alcohol c.Hydrazine (H 2 NNH 2 ) d.Methyl fluoride e.Hydrogen sulfide f.Carboxylic acid

69. 69 4.Arrange in order of increasing BP: CO 2 CH 3 OH CH 3 Br, RbF 5.Which one in each pair has the higher BP? a)CH 4 and C 2 H 6 b)H 2 S and H 2 Te c)NH 3 and PH 3 d)HCl and HF e)I 2 and ICl Intermolecular Forces: Examples

70. 70 Example (London Forces) 6. Arrange the following molecules in order of increasing strength of intermolecular forces. F 2 Br 2 Cl 2 I 2 7.Explain the trend in the normal boiling points of these liquids in terms of intermolecular forces. CH 4 normal boiling point: -161.5°C CF 4 normal boiling point: -28°C CCl 4 normal boiling point: +77°C CBr 4 normal boiling point: +190°C

71. 71 8. (11.100) Which of the following substances has the highest polarizability? CH 4, H 2, CCl 4, SF 6, H 2 S Intermolecular Forces: Examples

72. 72 Identify “intermolecular” forces 9.H 2 O 10.CH 2 Cl 2 11.KBr 12.F - + H 2 O 13.I 2 14.CH 3 OH 15.PCl 3 16.C 6 H 6 17.Fe 18.CS 2 19.BCl 3 20.Na + + NH 3 21. Dimethyl ether (CH 3 OCH 3 ) and ethanol (C 2 H 5 OH) have the same formula (C 2 H 6 O) but the BP of the ether is -25ºC and of the ethanol 78ºC. Explain.