1. versus By Daniel R. Barnes, init 11/14/2006

2. But before we get started... Do you remember when you read about “resonance structures” and learned they didn’t really resonate? Well, galloping gertie did. http://www.youtube.com/watch?v=j-zczJXSxnw&desktop_uri=%2Fwatch%3Fv%3Dj-zczJXSxnw&app=desktop (Thank you, Kristian Alarcon) CLICK ME

4. Page 238, Prentice Hall Chemistry: Electronegativity difference range Most probable type of bond Example 0.0 – 0.4 Nonpolar covalent H—H (0.0) 0.4 – 1.0 Moderately polar covalent H—Cl (0.9) 1.0 – 2.0 Very polar covalent H—F (1.9) >= 2.0Ionic Na + Cl - (2.1)

6. Formula = H2OH2O

7. electronegativity 2.1 3.5 -2.1 1.4 ++ -- ++

8. NOTE: Click in the grey to avoid jumping to the web page where this picture came from.

10. + - + - This attraction is an example of an “intermolecular force.” It is a specific kind of attraction called a “hydrogen bond”.

11. INTERMOLECULAR FORCES EXAMPLE: HYDROGEN BONDING

12. Attraction between water molecules causes “surface tension”

13. Hydrogen bonding between water molecules causes “surface tension”

14. Gravity  round planets/moons/stars Surface tension  round water droplets

16. Surface tension  Insect’s foot can’t get in between water molecules   Insect walks on water

19. See how her foot makes a dimple in the surface? Springs help provide tension. They pull the skin of the trampoline tight.

21. Hydrogen bonding  solidity and form of ice crystals

22. Unusual “open lattice” of ice crystal  Ice is less dense than water

26. + - + - s H2OH2OH2SH2S water hydrogen sulfide

27. + - + - s oxygen = 3.5 hydrogen = 2.1 ---------------------  = 1.4 Electronegativity comparison: sulfur = 2.5 hydrogen = 2.1 ---------------------  = 0.4 Electronegativity comparison: Bonding in a water molecule is...... “very polar covalent.” Bonding in a hydrogen sulfide molecule is...... on the borderline of “nonpolar” and “moderately polar”.

28. + - + - s + - + - s More polarity  Stronger attraction Less polarity  Weaker attraction

29. + - + - s + - + - s Stronger attraction  Molecules huddle together but free to wander Weaker attraction  Molecules fly away from each other + - + - + - + - + - + - + - + - s + - s + - s + - s + - s WATER is a LIQUID HYDROGEN SULFIDE is a GAS + - s + - s

30. - S This would be a good time to read that little passage from Fast Food Nation about hydrogen sulfide on page 178

31. ... and now for the other one...

32. 2.12.5 electronegativity 2.5 -2.1 0.4 Formula = C 8 H 18

33. No +’sNo -’s DISCLAIMER: C may be slightly negative & H slightly positive, but not enough to matter 2.1 2.5 + -

34. No +’sNo -’s

35. + - How do gasoline and water interact? No attraction, no repulsion. No minuses or plusses on the octane molecule, so...... whatever... Huh?... but...

36. + - + -... so...

43. Oily layer Watery layer Italian Salad Dressing

44. Oily layer Watery layer What kind of bonds are there in each layer? Example: C--H Example: O--H

45. Oily layer Watery layer As a result of polarity differences, how are atoms charged differently? + - + - 0 0 0 0

46. Q: Why is the bond between H & O polar, whereas the bond between H & C is nonpolar? A: H & C have electronegativities that are almost the same (2.1 & 2.5), whereas H & O have very different electronegativities (2.1 & 3.5).

47. Q: Why does Italian salad dressing separate into two layers? A: It contains polar materials and nonpolar materials.

48. Q: Why is the oily layer on the top rather than on the bottom? A: Oil is less dense than water.

49. Water is polar, so when you need to wash, you often need to add soap to the water to dissolve the nonpolar substances like fat, grease, and oil.

50. The sodium salt of a fatty acid “carbon backbone” H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H hydrocarbon  nonpolar covalent bonds Hydrogen and carbon atoms are neutral  Mixes with oily or watery materials? ?

51. The sodium salt of a fatty acid “carbon backbone” H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H hydrocarbon  nonpolar covalent bonds Hydrogen and carbon atoms are neutral  Mixes with oily or watery materials? ? ? O O ? Na+

52. nonpolar  oily  “hydrophobic” polar or charged  like water  “hydrophilic” Soap acts as a “bridge” between water and nonpolar materials. Soap sticks to both water AND oily materials, so the oil and water don’t have to separate

53. H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H Soap: part metal, part fat. Weird combo, huh?