Imforces

503 views

Published on

jajajajjajajajajaja

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
503
On SlideShare
0
From Embeds
0
Number of Embeds
5
Actions
Shares
0
Downloads
20
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Imforces

  1. 1. Intermolecular Forces of AttractionAttractive forces that cause atoms or molecules to stick together
  2. 2. MixturesElements orcompounds blendedtogether but notchemically combined
  3. 3. Mixtures Can be solid, liquid, or gaseous mixtures Solid mixture examples: Jewelry gold, most rocks, steel, alloys Liquid mixture examples Beverages, sea water, solutions Gaseous mixture examples Air, car exhaust
  4. 4. Mixtures Why do they form? What allows the parts to stay mixed? Why do they stay together? The components of a mixture are held together by IMF’s – intermolecular forces of attraction
  5. 5. IntermolecularForcesAll intermolecular forces are:• attractive forces• between molecules• do not make new compounds• Makes the molecules “sticky”• weaker than true “bonds”
  6. 6. Types of IMF’s London (dispersion) forces  all molecules  weakest interaction dipole-dipole forces  polar molecules ion-dipole forces  Between polar molecules and ions hydrogen bonding  H atoms w/ O, N, F not covalently bonded to it  strongest interaction
  7. 7. Polar forces• “Dipole - Dipole” interactions• positive ends attract negative ends of other molecules• about 1% as strong as a covalent bond
  8. 8. Dipole - Dipoleinteractions
  9. 9. London forces• Momentary dipole-dipole interaction• “instantaneous” dipole “induces” a dipole in a neighboring molecule• brief attractive force results
  10. 10. Step 1
  11. 11. Step 2
  12. 12. Result...
  13. 13. London forces• Strength depends on:• size of electron cloud – bigger = stronger• number of atoms in molecule – more atoms = more electrons = stronger
  14. 14. Ion – dipoleforces• Between polar molecules and ions • Aqueous solutions of ions• Positive ends of polar molecules attract negative ions• Negative ends attract positive ions• Only important in aqueous solutions
  15. 15. Hydrogen Bonds• Special case of polar attraction• H atom is • 1)bonded to high EN atom and • 2)attracted to a high EN atom it is not bonded to (N, O, F)• 5 times stronger than regular polar attractions
  16. 16. Hydrogen Bonds
  17. 17. Physical property effects of I nter m olecular F orces of A ttraction…all come down to how stickythe molecules are towardeach other…
  18. 18. The Key Idea…The stronger theIMF’s, the tighter themolecules cling toeach other, the harderit is to separate them.
  19. 19. The Key Idea…In other words, the harder it is to separate molecules, the stronger their IMF’s
  20. 20. What does thatmean…”separate themolecules”?Pull them apart: Melting Boiling Physically move them apart Peel them away. Wipe them off, etc…
  21. 21. Boiling PointEffectsFormula Boiling Polar? IM force pointHCl -85oC Polar Dipole- dipoleH 2S -60.7oC Polar Dipole- dipoleH 2O 100oC Polar H-bondingAr -185.7oC Nonpolar london
  22. 22. Boiling PointEffectsFormula Boiling Polar? IM force PointF2 -188.1oC Nonpolar LondonCl2 -34.6oC Nonpolar LondonBr2 58.8oC Nonpolar LondonI2 184.4oC Nonpolar London
  23. 23. Boiling PointEffectsFormula Boiling point Polar? IM forceCH4 -161.5oC Nonpolar LondonC 2H6 -88.6oC Nonpolar LondonC 3 H8 -42.1oC Nonpolar LondonC4H10 -0.5oC Nonpolar LondonC5H12 36.1oC Nonpolar london
  24. 24. Intermolecular Forces of AttractionAttractive forces that cause atoms or molecules to stick together
  25. 25. Types of IMF’s London (dispersion) forces  all molecules  weakest interaction dipole-dipole forces  polar molecules ion-dipole forces  Between polar molecules and ions hydrogen bonding  H atoms w/ O, N, F not covalently bonded to it  strongest interaction
  26. 26. The Key Idea…The stronger theIMF’s, the tighter themolecules cling toeach other, the harderit is to separate them.
  27. 27. Solubility of a solid inliquidGeneral rule: Like dissolves Like• Polar solutes dissolve in polar solvents • Sugar (polar solute) in H2O (polar solvent)• Ionic solids dissolve in polar solvents • NaCl (ionic solid) in H2O (polar solvent)• Nonpolar solutes dissolve in nonpolar solvents • Dried paint (nonpolar solute) in paint stripper – turpentine, etc. (nonpolar solvent)
  28. 28. Colligative properties ofSolutions-Properties of solutions that are affected by the number of dissolved particles, not the identity of the particlesExample: vapor pressure loweringThe more particles (with little tendency to vaporize) that are added to a solvent, the lower the vapor pressure of the solution becomes
  29. 29. Colligative properties ofSolutionsDensity of a solutionThe presence of dissolved particles (whose mass is greater than the mass of the solvent particles) in a solution causes the density of a solution to increase• Sugar water is more dense than pure water• Sugary sodas are more dense than diet sodas • it takes more sugar molecules than artificial sweetener molecules
  30. 30. Swimming in the DeadSea
  31. 31. Colligative properties ofSolutionsBoiling point elevation :The presence of dissolved particles tends to increase the boiling point of a liquidSalt added to water before boiling to prepare food increases the temperature the water boils at, and thus cooks the food faster, as the
  32. 32. Colligative properties ofSolutionsFreezing point depressionThe presence of dissolved particles tends to lower the freezing point of a liquidSalt or other substances are used to melt ice, because as they dissolve into the ice, they lower the freezing point of the ice, and thus even more of the ice melts
  33. 33. Compressibility• gases are compressible – empty space between molecules – Weak IMF’s won’t keep molecules together• liquids, solids aren’t – closely packed
  34. 34. Diffusion• The intermingling of molecules with each other• gases = rapid  much empty space• liquids = slowly  more closely packed• solids = negligible  locked in place
  35. 35. Cohesion/Adhesion Cohesion = molecules sticking together Adhesion = molecules sticking to a substrate
  36. 36. Viscosity• The resistance of a fluid to flow.• The stronger the IMF’s, the higher the viscosity
  37. 37. Surface Tension• Intermolecular attractions at the surface are only inward towards the substance
  38. 38. Surface Tension ,continued• Molecules at the surface of a liquid act as a “skin”• the greater the IMF’s, the more pronounced the effect• liquids seek to lower their surface tension• water drops are spherical
  39. 39. Surface Tension ,continued
  40. 40. Surface Wetting• The spreading of a liquid across a surface• must have adhesion ≈ cohesion
  41. 41. Gasoline – a nonpolarhydrocarbon• Low surface tension – only London forces• low cohesion – spreads easily across most surfaces• does not effectively “wet” glass
  42. 42. H2O – a polar molecule that H-bonds• High surface tension – hydrogen bonding• High cohesive forces• High adhesive forces – will H-bond with O’s in glass• Good wetting agent for glass
  43. 43. • Water beads on greasy glass – eliminates H-bonding to glass – low adhesion
  44. 44.  Surfactants , used in soaps and detergents, drastically lower the surface tension of water – soapy water spreads more easily over dirty surfaces
  45. 45. Vaporization• The change of a liquid → gas is called vaporization • an example of separating molecules• Evaporation: happens at the exposed surface of a liquid• Boiling: happens within the liquid itself
  46. 46. Evaporation• Liquids exert vapor pressure due to the evaporated liquid• The stronger the IMF’s, the slower the evaporation rate, the lower the vapor pressure for a given temperature
  47. 47. Evaporation• The higher the T of a substance, the more molecules with enough energy to overcome cohesive forces/surface tension and evaporate• As liquid T ↑, vapor P ↑
  48. 48. Temperature is ~ theaverage KE of a sample coolest warmestAbundance Energy Minimum E to evaporate
  49. 49. What happens...• To the evaporation rate – if the temperature = the boiling point ?• All the molecules, on average, have enough energy to vaporize – the liquid boils
  50. 50. What happens...• If the vapor pressure equals the atmospheric pressure ?• All the molecules, on average, have enough energy to vaporize – the liquid boils
  51. 51. T vs VaporPressureVa 1.00 atmpPressure Temperature 100oC
  52. 52. How can you boil aliquid?1) Heat it to its boiling point vapor P = air P1) Reduce the air P above it to equal the vapor P of the liquid at that temperature • air P = vapor P all done!
  53. 53. Intermolecular Forces of AttractionForces of attractionbetween molecules

×