Intermolecular Forces and Liquids and Solids

1. Intermolecular Forces and Liquids and Solids Chapter 11

2. A phase is a homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary. 2 Phases Solid phase - ice Liquid phase - water Depends on the intermolecular distance

3. Intermolecular Forces Intermolecular forces are attractive forces between molecules. Intramolecular forces hold atoms together in a molecule. • Intermolecular vs Intramolecular • 41 kJ to vaporize 1 mole of water (inter) • 930 kJ to break all O-H bonds in 1 mole of water (intra) “Measure” of intermolecular force boiling point melting point DHvap DHfus DHsub Generally, intermolecular forces are much weaker than intramolecular forces. Chemical bonding and physical properties!

4. Orientation of Polar Molecules in a Solid Intermolecular Forces Dipole-Dipole Forces Attractive forces between polar molecules So higher dipole, larger attractive force.

5. Ion-Dipole Interaction Intermolecular Forces Ion-Dipole Forces Attractive forces between an ion and a polar molecule Small r, larger F

6. Interaction Between Water and Cations Hydration(水合) in solution

7. Intermolecular Forces Dispersion Forces 分散力(also be called as London Force) Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules ion-induced dipole interaction dipole-induced dipole interaction

8. Dispersion Forces 極化率 The polarizability: the ability to distortion the electron distribution of a molecular or atoms. Normally, large amount of electrons or low-density electron cloud will show higher polarization Dispersion force is the transition of the dipole-induced attraction So He or N2 gas/non-polarized maculars can be condensed in low-temperature.

9. Induced Dipoles Interacting With Each Other Transition state

10. Intermolecular Forces Dispersion Forces Continued Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted. • Polarizability increases with: • greater number of electrons • more diffuse electron cloud Dispersion forces usually increase with molar mass. Some dispersion force larger than polarized dipole-dipole force! e.g. CCl4 (76.5o)shows higher boiling point than CH3F(-78.4o)

11. O O S What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH4 CH4 is nonpolar: dispersion forces. SO2 SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules.

12. or … … H H B A A A Intermolecular Forces Hydrogen Bond The hydrogen bond is a special dipole-dipole interaction between they hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A & B are N, O, or F

13. Decreasing molar mass Decreasing boiling point Why is the hydrogen bond considered a “special” dipole-dipole interaction?

14. Hydrogen Bond HCOOH and water

15. The average hydrogen bond is ~ 40KJ/mol. The strength of hydrogen bond depends on the electronegativity Of atoms. e.g. HF shows higher strength than H2O. However, H2O shows Higher boiling point than HF? Each H2O have 4 H-bond.

16. Properties of Liquids Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area. Strong intermolecular forces High surface tension

17. H2O show very strong H-bond, therefore shows higher surface tension than other liquid

18. Polarized molecular and non-polarized molecular

19. Adhesion Cohesion Properties of Liquids Cohesion is the intermolecular attraction between like molecules Adhesion is an attraction between unlike molecules

20. Properties of Liquids Viscosity is a measure of a fluid’s resistance to flow. Strong intermolecular forces High viscosity

21. Viscosity CH2-OH 甘油 Similar to H2O, it shows high H-bond

22. 3-D Structure of Water Maximum Density 4°C Density of Water Ice is less dense than water Water is a Unique Substance 2 共價鍵 2氫鍵

23. ice benzene

24. lattice point Unit cells in 3 dimensions Unit Cell A crystalline solid possesses rigid and long-range order. In a crystalline solid, atoms, molecules or ions occupy specific (predictable) positions. An amorphoussolid does not possess a well-defined arrangement and long-range molecular order. A unit cell is the basic repeating structural unit of a crystalline solid. • At lattice points: • Atoms • Molecules • Ions

25. Seven Basic Unit Cells

26. Three Types of Cubic Unit Cells

27. Arrangement of Identical Spheres in a Simple Cubic Cell

28. Arrangement of Identical Spheres in a Body-Centered Cubic Cell

29. A Corner Atom, a Edge-Centered Atom and a Face-Centered Atom Shared by 2 unit cells Shared by 4 unit cells Shared by 8 unit cells

30. Number of Atoms Per Unit Cell 1 atom/unit cell 2 atoms/unit cell 4 atoms/unit cell (8 x 1/8 = 1) (8 x 1/8 + 1 = 2) (8 x 1/8 + 6 x 1/2 = 4)

31. Relation Between Edge Length and Atomic Radius

32. d = d = m m V V x = x 1 mole Ag 107.9 g 7.17 x 10-22 g 6.022 x 1023 atoms mole Ag 6.83 x 10-23 cm3 When silver crystallizes, it forms face-centered cubic cells. The unit cell edge length is 409 pm. Calculate the density of silver. V = a3 = (409 pm)3 = 6.83 x 10-23 cm3 4 atoms/unit cell in a face-centered cubic cell m = 4 Ag atoms = 7.17 x 10-22 g = 10.5 g/cm3

33. Closest Packing

34. Closest Packing

35. HCP and CCP AB stacking ABC stacking

36. X-Ray Diffraction (XRD)X-光繞射光譜

40. Applications: MoS2 crystalline

41. Applications: Graphite oxide ~ 11 o

42. XRD

43. The crystal types: • Ionic crystals • Covalent Crystals • Molecular Crystals • Metallic Crystals

44. Types of Crystals • Ionic Crystals • Lattice points occupied by cations and anions • Held together by electrostatic attraction • Hard, brittle, high melting point • Poor conductor of heat and electricity CsCl ZnS CaF2

45. EX: KH2PO4

46. NaCl(FCC)

47. carbon atoms Types of Crystals • Covalent Crystals • Lattice points occupied by atoms • Held together by covalent bonds • Hard, high melting point • Poor conductor of heat and electricity graphite diamond

48. From graphite to graphene Graphene Graphite Slice down to Atomic layer

49. What is graphene? • Imagine a piece of paper but a million times thinner. This is how thick graphene is. • The thinnest while strongest material in the world! (0.77 mg/1m2 Graphene, can sustain 4 kg ) • Imagine a material more conducting than silver. This is how conductive graphene is. Image from Nobel committee From a recently interview with A. K. Geim.

50. Electrical properties of Graphene Graphene resistivity: 1.0x10-8 Ohm m Also, it’s current density is > 1.0X108 A/cm From wikipedia