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Polar

Polar. +. -. versus. Nonpolar. 0. 0. By Daniel R. Barnes, init 11/14/2006. Mr. Barnes, please show folks the gasoline/water bottle and pass it around. CLICK ME. http://www.youtube.com/watch?v=j-zczJXSxnw&desktop_uri=%2Fwatch%3Fv%3Dj-zczJXSxnw&app=desktop (Thank you, Kristian Alarcon).

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Polar

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  1. Polar + - versus Nonpolar 0 0 By Daniel R. Barnes, init 11/14/2006

  2. Mr. Barnes, please show folks the gasoline/water bottle and pass it around.

  3. CLICK ME http://www.youtube.com/watch?v=j-zczJXSxnw&desktop_uri=%2Fwatch%3Fv%3Dj-zczJXSxnw&app=desktop (Thank you, Kristian Alarcon) 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.

  4. SWBAT . . . . . . predict bond type when given two elements

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

  6. Of course, when the two elements are a couple of metals, they will form a metallic bond, not a covalent or ionic bond.

  7. SWBAT . . . . . . explain the causes and effects of hydrogen bonding.

  8. shared electron pair covalent bond = Formula = H2O water molecule

  9. electronegativity 3.5 -2.1 d+ d+ 1.4 2.1 unequal sharing of electrons 3.5 "polar covalent bonds" d-

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

  11. + + - - This attraction is an example of an “intermolecular force.” This strong attraction makes it hard for water to be a gas. It is a specific kind of attraction called a “hydrogen bond”.

  12. INTERMOLECULAR FORCES EXAMPLE: HYDROGEN BONDING

  13. Hydrogen bonding gives water a high boiling point and a high melting point compared to molecules of similar size.

  14. Ar H H Argon: MW = 18 BP = -186oC C C H H Water: MW = 18 BP = +100oC H H H H H H H H O O N N N N BOILING POINT Nitrogen: MW = 28 BP = -196oC Methane: MW = 16 BP = -161oC Oxygen: MW = 32 BP = -183oC Ar O O O O

  15. Attraction between water molecules causes “surface tension”

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

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

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

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

  20. Hydrogen bonding  solidity and form of ice crystals

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

  22. Bond type Properties

  23. + + s - - H2O H2S ? ? hydrogen sulfide water

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

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

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

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

  28. . . . and now for the other one . . .

  29. nonpolar covalent 2.5 -2.1 2.1 2.5 electronegativity hydrogen carbon 0.4 Formula = octane C8H18

  30. nonpolar covalent 2.5 2.1 + - No +’s No -’s "negligible" DISCLAIMER: C may be slightly negative & H slightly positive, but not enough to matter

  31. nonpolar covalent No +’s No -’s

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

  33. + + - - . . . so . . . . . . but . . .

  34. Italian Salad Dressing Oily layer Watery layer

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

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

  37. more CHECKS FOR UNDERSTANDING 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).

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