1. Intermolecular Forces: What holds everything together (Chapter 14)

2. Intramolecular forces (bonds) Hold atoms together in molecules Have high energy associated with them –it’s difficult to break molecules into their individual atoms Different types based upon what is going on with the electrons (electron clouds)

3. Types of bonds: Ionic –attraction between fully charged molecules/ atoms NaCl, made from Na + and Cl - ; or Ca(OH) 2, made from Ca 2+ and 2OH - Covalent –electrons are shared between atoms, water (H 2 O) and sugar (C 6 H 12 O 6 ) –Can be polar or nonpolar Based on –electronegativity –VSEPR geometry (shape)

4. Intermolecular forces (IMFs) Hold molecules together Much weaker than intramolecular forces –Intramolecular bonds are usually 100x or even 1000x stronger *(kJ are units of energy like Calories; 1Cal= 4.184kJ) –1000cal= 1Cal –1cal =4.184J

5. Figure 14.2: Intermolecular forces exist between molecules. Bonds exist within molecules.

6. Why do we care? The strength of the IMFs determine the state of matter –Solid, liquid, or gas* –*Not plasma- intramolecular bonds are broken to get plasmas

7. shapevolumedensityenergy* motion with Energy* level of organizatio n* strength of IMFs* Gas indefinite variable with P and T variable with volume change high high; molecules freely moving with great distance compared to molecular size between them very lowlow Liquid indefinite constant ** moderate high; molecules freely moving past each other but in close proximity to each other low moderate Solid definite constant ** low low; vibration only as molecules are basically fixed in place high * all at room temperature, ~25C **small variations occur due to temperature changes, very little variable with pressure changes Solids, Liquids, and Gases

8. Things with strong IMFs tend to be solids at room temperature Things with weak IMFs tend to be gases at room temperature Medium IMFs tend to be in between- –liquids, yes, but with varying characteristics Amorphous solids: long transition between solid and liquid states- gets soft, then melts (like wax) Crystalline solids: definite, clear melting point (no soft transition- ie: ice)

9. Types of IMFs In order of increasing strength: –London dispersion forces –Dipole- dipole –Hydrogen bonds

10. London dispersion forces LDFs occur in all molecules, but are the only forces that are present in nonpolar molecules such as diatomic molecules and atomic substances –CO 2, N 2, He They occur because the electron clouds around molecules are not always evenly distributed. –When the electron clouds are unevenly distributed, temporary partial charges result

11. Figure 14.6: Atoms with spherical electron probability. 14.6: The atom on the left develops an instantaneous dipole.

12. LDFs, con’t These temporary partial charges are called induced or temporary dipoles –This temporary dipole forming in a nonpolar substance is strong enough to cause a dipole to occur in a neighboring molecule

13. Figure 14.3: (a) Interaction of two polar molecules. (b) Interaction of many dipoles in a liquid.

14. LDFs, con’t Basically, everything lines up temporarily, but long enough to keep everything together Common in gases

15. See LDFs at work here http://antoine.frostbur g.edu/chem/senese/ 101/liquids/faq/h- bonding-vs-london- forces.shtml http://antoine.frostbur g.edu/chem/senese/ 101/liquids/faq/h- bonding-vs-london- forces.shtml These dipoles fluctuate; they do not last very long, but they do occur frequently enough to have a significant effect overall

16. Dipole- dipole forces: Are stronger than LDFs because they occur in polar molecules that already have permanent dipole moments (in other words, partial charges already exist) Are AKA as van der Waals interactions at times, but in actuality both induced dipole attractions and dipole-dipole attractions are van der Waals forces

17. Examples HCl and other acids* HCN NH 3 *except HF, which does something else

18. What would happen between polar and nonpolar molecules? (Do forces of attraction exist? Do the molecules repel?) Explain!

19. Hydrogen bonding Are stronger than dipole-dipole forces or LDFs Occurs in only the most polar bonds –between molecules containing H-F, H-O and H-N bonds only Are the reason that water is so different from any material from similar atoms, like H 2 S

20. Figure 14.4: Hydrogen bonding among water molecules. Norton Interactive: IMFs tutorial Select Hydrogen bonding in water from bottom of listFigure 14.4: Hydrogen bonding among water molecules. Norton Interactive: IMFs tutorial Select Hydrogen bonding in water from bottom of list Norton Interactive Norton Interactive

21. http://www.northland.cc.mn.us/biology/Biology1111/animations/hydrogenbo nds.html http://www.northland.cc.mn.us/biology/Biology1111/animations/hydrogenbo nds.html (note: I am not responsible for the music on the above web site) Polarity and hydrogen bond formation Polarity and hydrogen bond formation Ice at different temperatures Ice at different temperatures

22. Which is ice? Which is liquid water? Explain. Ice at different temperatures Ice at different temperatures

23. Water is special because… It has a high specific heat, meaning that it takes a lot of energy to raise the temperature of a sample of water by even 1 degree –Specific heat of water (c)= 1 cal/ g°C or 4.184J /g°C The solid phase is LESS dense than the liquid phase, so ice floats on water It’s a good solvent for many substances due its polarity H 2 O is liquid at RT, where H 2 S is a gas

24. Figure 14.5: The boiling points of covalent hydrides.

25. Water is special And water would not be special without hydrogen bonding H bonding plays vital roles in biological systems –DNA (holding together the chains of DNA) –Protein shape (and therefore the protein’s function; think hair!) enzymes

26. IMFs in proteins IMFs in proteins

27. For the next slide: Determine polarity of group Determine type of IMFs are possible in group Determine if the group will be highly soluble in water

28. Sickle Cell Anemia Glu (glutamic acid) replaced by Val (valine) synthesis

29. What would happen if a molecule capable of H-bonding comes into contact with: –A nonpolar substance –A polar substance that does not H-bond

30. Strength increases from left to right; when ions are involved, attractive forces are greater than when they are not involved. http://cwx.prenhall.com/bookbind/pubbooks/blb/chapter11/medialib/blb1102.html

31. Dealing with this pic… Ion- dipole forces Ionic Bonding –Basically electrostatic attractive forces between positive and negative charges Strong

32. IMFs influence… Boiling point/ Melting Point Viscosity Surface Tension Capillary Action Vapor pressure/ rate of evaporation State of Matter (at room temp) –Density falls here, but can vary even within state

33. IMFs and mass The mass of a material makes a difference, so yes, mass (size) matters Larger molecules have stronger forces than similar molecules that are smaller (in terms of mass)

34. Figure 14.5: The boiling points of covalent hydrides.

35. Boiling points and masses of noble gases Helium: -269°C4.00 g/mol Neon: -246°C20.18 g/mol Argon: -186°C39.95 g/mol Krypton: -152°C83.80 g/mol Xenon: -108°C131.3 g/mol radon -62°C~222 g/mol Larger atoms have larger e- clouds, which lead to greater polarizability

36. Name MolecularMeltingBoilingState at FormulaPoint 25 o C ( o C) methaneCH 4 -183-164gas ethaneC2H6C2H6 -183-89gas propaneC3H8C3H8 -190-42gas butaneC 4 H 10 -138-0.5gas pentaneC 5 H 12 -13036gas hexaneC 6 H 14 -9569gas heptaneC 7 H 16 -9198gas octaneC 8 H 18 -57125gas nonaneC 9 H 20 -51151liquid decaneC 10 H 22 -30174liquid undecaneC 11 H 24 -25196liquid dodecaneC 12 H 26 -10216liquid eicosaneC 20 H 42 37343liquid triacontaneC 30 H 62 66450solid Saturated Hydrocarbons, or Alkanes As melting point increases, boiling point increases (saturated hydrocarbons are hydrocarbons with as many Hs as possible)

37. Shape also matters Butane, bp -0.5 degrees C 2-methylpropane -11.7 degrees C Butane has a higher boiling point because the dispersion forces are greater. The molecules are longer (and so set up bigger temporary dipoles) and can lie closer together than the shorter, fatter 2-methylpropane molecules. Also, the molecules can stack with each other better

38. Butane and 2-methylpropane Compare the properties of these two compounds: n-butane.............................. 2-methylpropane 0.601................ relative density (liquid)................ 0.551 1.348................ refractive index (liquid)................1.351 - 0.5.................. boiling point ( o C)..................... - 11.7 - 138.3................ melting point ( o C)................... - 159.6 It is clear that the different carbon skeletons make a difference to the properties, especially the melting and boiling points.

39. Fats v Oils: Saturated v. Unsaturated Molecular size, bond order, and bond orientation: –How different IMFs result in differences in food molecules

40. A carbon exists where two lines intersect Atoms other than C and H are written in Hs are not usually written out- –They fill in to complete octets on other atoms

41. Random cis trans fats (Omega 3 and Omega 6 fats have the double bonds on the 3 or 6 th carbon)

42. fatty acids and triglycerides fatty acids and triglycerides 3 Fatty acid chains (above) join with a glycerol molecule (top right) to form a triglyceride (right, saturated)

43. Triglyceride formation

44. Triglycerides Oils –More unsaturated FAs –Liquid at RT Fats –More saturated FAs –Solid at RT

45. 16C sat MP= 62.9°C 18C sat MP= 69.6°C 18C unsat MP= 13°C

46. Oleic v linoleic acid Melting Points °C: –Oleic acid: 13 –Linoleic Acid: -5

48. Why? Why do the melting points differ between –Palmitic Acid (16 C, sat) –Stearic Acid (18 C, sat) –Oleic Acid (18C, mono unsat) –Linoleic Acid (18C, polyunsat. 2=) Explain the impact of number of carbons and the number of double bonds when answering the above question

49. WHY DOES THIS HAPPEN? Proximity of atoms; regular shape allows the IMFs to hold everything in place (to “stack”) molecules rather than have the irregular shapes slide past each other

50. Triglycerides In unsaturated triglycerides, the molecules can not stack In the saturated molecules, the fatty acids are tightly packed and stacked

51. More carbons, higher MP The more double bonds, the lower the MP

52. Of the following, which would have the highest MP? The lowest? Lauric 12C, unsat, MP +44°C Stearic 18C, sat, MP 70°C Arachodonic 20, unsat, MP -50°C Elmhurst

53. Which fats are saturated? Unsaturated? What type of IMF would predominate ? Rank the molecules in order from lowest to highest MP.

54. Percent Fatty Acids in Percent Fatty acids in selected triglycerides Percent Fatty acids in selected triglycerides

55. Cis and trans fats

56. Cis- v Trans- fats Cis- fats are naturally occurring fats from animal products Trans- fats occur from modifying oils chemically –Partially hydrogenating oils Adding H’s causes double bonds to convert to single bonds –Unsaturated to saturated conversion Due to steric hindrance, when the H is added, they convert some cis bonds to trans bonds Why do manufacturers make trans fats for use in foods? –Trans fats cost less (vegetable sources v. animal sources) –Fats in foods are usually more desirable that oils- Less greasy Can control how solid the fats are by controlling the number of double bonds Better/ easier to cook with (especially in baked goods)

57. Saturated Fats: These are considered to be the “bad” fats. –called “saturated” because their carbon structures are completely filled (saturated) with hydrogen atoms. –chemical structure is very linear which allows for a “stacking” effect to occur. –stacking is what promotes the solidifying effect of most saturated fats (butter, lard, most animal fats). –solidification may also occur in the body which partly explains the artery-clogging effects linked to saturated fats. –Examples of saturated fats include myristic acid, palmitic acid, stearic acid, arachidic acid, and lignoceric acid. These fats may raise cholesterol levels in the body and should be used in moderation

58. Why are trans- fats bad? The trans- double bonds –Are more reactive in the body Promote free radical formation –Leads to destruction of biomolecules –Are more likely to clog arteries Due to shape, get caught in body –Promote cholesterol levels to increase, since they can be used to make cholesterol in the body –We don’t have the enzymes to process the trans- fats (we can process cis- fats)

59. http://www.nhlbi.nih.gov/chd/Tipsheets/images/satfatgraph.gif Good fat/ Bad fat? Good fat/ Bad fat?

60. Spider silk monomer (amino acid) –Amino acid R groups Amino acid R groupsAmino acid R groups Kevlar monomer

61. Silk Silk and proteins Silk and proteins

62. Viscosity Viscosity is the resistance to flow –The greater the viscosity, the greater the resistance to flow –Determined: How quickly a fluid flows through a tube under gravitational force (slower= more viscous) –Or by Determining rate at which steel sphere fall through the liquid (more viscous= more slowly) –Changes as temperature changes

63. What is surface tension? Resistance of a liquid to an increase in it’s surface area (Zumdahl) Free energy per unit surface area (Tinoco, Sauer, Wang and Puglisi) –Force per unit length (mNm -1, or dyne/cm) Layman’s terms: How much something spreads out on a surface –Beading up= high surface tension –Spreading out= low surface tension

64. Surface Tension http://home.earthlink.net/~dmocarski/chapters/chapter7/main.htm (High surface tension)(Low surface tension) The molecules of water have more adhesion to the (polar) glass than to each other (cohesion); The Hg has more cohesive forces than attraction to the glass Cohesion: Molecules sticking (due to IMFs) to the same molecule in a pure compound Adhesion: Molecules sticking (due to IMFs) to other molecules adjacent to the pure compound –(not a mixture- at a surface interface)

65. Wetting and Dewetting http://www.mpikg-golm.mpg.de/gf/1

66. Wetting is how water (in this case) adheres to a surface; when the surface tension is lowered, the material becomes wetter. Surface tension of water is 73 dyne/ cm; http://home.att.net/~larvalbugrex/striders.html Water droplet on lotus leaf, with adhering particles

67. What causes surface tension? Surface tension is a result of the imbalance of forces at the surface (or interface) http://www.kibron.com/Science/ http://home.earthlink.net/~dmocarski/chapters/chapter7/main.htm

68. Surface tension of… mNm -1 Temperature (˚C) Platinum 1819200 Mercury 48715 Water 71.9725 Water 58.85 100 (liquid) Benzene 28.920 Acetone 23.720 n- Hexane 18.420 Molten Iron 171600 Silicon Oil 16.925 Neon 5.2-247 (Tinoco, Sauer, Wang, and Puglisi); http://www.boldinventions.com/tsun_sim_2.html

69. Does temperature matter? Yes- part of the reason that we wash in warm water (at times), not cold – the fabric gets “wetter” As temperature increases, surface tension decreases (Surface tension given for water against air) surface tension (mNm -1 ) -877 -576.4 075.6 574.9 1074.22 1573.49 1873.05 2072.75 2571.97 3071.18 4069.56 5067.91 6066.18 7064.4 8062.6 10058.9 temperature ( C) http://scienceworld.wolfram.com/physics/SurfaceTension.html

70. Temperature and IMFs IMFs in a substance change in strength in a substance as temperature changes This influences certain properties of the substances –Surface tension –Viscosity –Capillary action –Vapor pressure (but not BP, MP)

71. Capillary Action http://home.earthlink.net/~dmocarski/chapters/chapter7/main.htm Capillary action: a phenomenon associated with surface tension and resulting in the elevation or depression of liquids in capillaries (from www.dictionary.com) The molecules of water have more adhesion to the (polar) glass than to each other (cohesion); The Hg has more cohesive forces than attraction to the glass (glass is polar)

72. Vaporization and Vapor Pressure The molecules in a sample of a liquid move at various speeds –(average speed is the temperature; some have more energy, some have less, but the overall KE is temperature) Sometimes molecules at the surface have sufficient speed to overcome the attractive forces and leave the liquid surface (thus vaporizing)

73. Figure 14.9: Microscopic view of a liquid near its surface.

74. Dynamic equilibrium Dynamic equilibrium is the state where there is simultaneous and equal vaporization and condensation of the substance In a closed container, at some pressure, the amount that vaporizes will equal the amount condensing on the surface of the liquid –This is the equilibrium vapor pressure

75. VP and IMFs Stronger IMFs equal lower vapor pressures –Less likely to evaporate Weaker IMFs equal higher vapor pressures –Substance with very low IMFs and therefore high vapor pressures evaporate very quickly and easily Called volatile substance Mass and shape important, just like with boiling point –Heavier = lower VP ex: oil –Lighter= higher VP ex: alcohol More volatile Think propane (C 3 H 8 ) v. gasoline (C 8 H 18 )

76. VP and Boiling Vaporization occurs at any temperature, but occurs more rapidly as temperature increases –Molecules at the surface would have to have more speed to overcome the IMFs –Boiling is the point at which the vapor pressure equals the external pressure on the surface of the liquid Molecules are able to “escape” liquid phase b/c they have enough Energy to break the IMFs –Convert PE of IMFs to KE of motion in a gas

77. Boiling and VP, con’t Liquids have some air dissolved in them in tiny invisible bubbles As water vaporizes in the liquid, it is added to the bubbles Also, the gas bubbles are expanding because they are being heated; this causes an increase in volume, but not mass –At this point, 2 things are going on: This decreases density, causing the bubbles to float to the surface Also, as gas expands, the pressure increases – –When the pressure of the bubble increases to greater than the vapor pressure at the surface, the liquid is boiling All molecules must be vaporized before a further increase in temperature can occur –Need to break all IMFs (convert all PE of IMFs before increasing KE of molecules)

78. Boiling Point and Elevation As elevation on the Earth’s surface increases, the atmospheric pressure decreases –(smaller column of air pushing down on the area; therefore less pressure) Boiling point changes as the atmospheric pressure changes If you could decrease the pressure without changing temperature, the substance would boil at a lower temperature –A decrease in pressure results in a decrease in BP

79. Figure 14.14: The formation of the bubble is opposed by atmospheric pressure.

80. Energy Changes Accompanying Changes of State Think back: Each change of state is accompanied by a change in the energy of the system – –Whenever the change involves the disruption of intermolecular forces, energy must be supplied The disruption of intermolecular forces accompanies the state going towards a less ordered state (higher entropy) – –As the strengths of the intermolecular forces increase, greater amounts of energy are required to overcome them during a change in state Takes more energy to go from – –a liquid to a gas than – –from a solid to a liquid Removing energy allows the molecules to “self- organize”, and results in an more ordered state – –Lower entropy

81. Heat of Fusion The melting process for a solid is also referred to as fusion – –The enthalpy change associated with melting a solid is often called the heat of fusion (Δ H fus ) Ice ΔH fus = 6.01 kJ/mol – –Δ H is a change (Δ) in enthalpy (H), a measure of energy that is much like heat, but takes into account a few other factors

82. Heat of Vaporization The heat needed for the vaporization of a liquid is called the heat of vaporization (Δ H vap ) Water Δ H vap = 40.67 kJ/mol Vaporization requires the input of heat energy

83. Less energy is needed to allow molecules to move past each other than to separate them totally, – –so ΔH fus < Δ H vap

84. The heating/cooling curve for water heated or cooled at a constant rate.

85. Energy/ disorder diagram

86. Energy and IMFs Remember Kinetic energy is the Energy associated with moving particles Heat is the RANDOM KE of an object –(as opposed to directional motion) Temperature is the measure of the AVERAGE KE in a substance When IMFs are disturbed due to E changes, the properties of the substance change, even to the point of changing state because the PE of the molecules changes

87. Think of IMFs like magnets: stronger magnets hold things more firmly together –The more firm the connections, the less molecular motion can occur with the same amount of Energy added –Adding (or removing) energy from the system can overcome (or increase) the IMFs, and cause a change in state Add Energy, move from S -> L -> G –Endothermic process Remove Energy, move from G -> L -> S –Exothermic process

88. Air conditioners take advantage of Energy changes to remove heat energy from a warm indoor environment by vaporizing condensed gas On the outdoor portion of the AC unit, the gas is condensed to a liquid, sending the heat energy to the environment

89. Phase Diagram Due to changes in pressure and temperature, a substance can exist in all three states under specific conditions –The Triple Point Think foggy icy days

90. Explain how the lava lamp works (not “you plug it in”! On a molecular level, explain what is happening to the materials and their IMFs- this is beyond how we answered this question earlier this year!)