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When Intermolecular Forces Rule in Chemistry and Biology

When Intermolecular Forces Rule in Chemistry and Biology. PGCC CHM 101 Sinex. Comparison of properties for the states of matter. The liquid state of matter. Molecules are closely packed but free to move about randomly. There must be a force of attraction between the molecules.

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When Intermolecular Forces Rule in Chemistry and Biology

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  1. When Intermolecular Forces Rulein Chemistry and Biology PGCC CHM 101 Sinex

  2. Comparison of properties for the states of matter

  3. The liquid state of matter Molecules are closely packed but free to move about randomly. There must be a force of attraction between the molecules.

  4. As molecules start to vaporize Molecules are great distances apart in gaseous state but free to move about randomly. What about in solids? Click here for a simulation of the states of matter

  5. Force-distance relationship For the Fattraction proportional to 1/distance molecules in contact with each other

  6. Force-distance relationship 1

  7. Force-distance relationship 2

  8. Force-distance relationship 3

  9. Force-distance relationship 4

  10. Force-distance relationship 5 Less than 20% the strength at 5 molecular distances

  11. Increasing strengths of IMF The strength of IMF’s • H-bonding (fixed distance ~200 pm) • Ion-ion (1/r) • Ion-dipole (1/r2) • Dipole-dipole (1/r3) • Ion-induced dipole (1/r4) • Dipole-induced dipole (1/r6) • Induced dipole-induced dipole (1/r6) Inverse functions of distance to various powers How do the other functions behave compared to 1/r? Click here for an interactive Excel spreadsheet to explore

  12. O-H 96 pm covalent bond … O H 186 pm Hydrogen bonding in water Click here for Chime activity

  13. Base Pairs in DNA: H-bonding AT pair                            GC pair Why not here? Click here for Chime structure of DNA Click here for Chime activity

  14. Lipid Bilayer: Induced Dipole – Induced Dipole Interaction for Hydrocarbon Chains phospholipid Click here for Chime activity

  15. What holds the iodine molecules together in solid iodine? 272 pm for I2 covalent bond 427 pm between two molecules in crystalline structure About half an iodine atom space between molecules

  16. Why do low molar mass substances that are non-polar molecules, such as H2, N2 O2, or CO2 have very low boiling points? Since they are non-polar, the IMF will be induced dipole- induced dipole, which is the weakest IMF. To get the molecules to interact with one another, the temperature needs to be decreased considerably (lower kinetic energy).

  17. For an ideal gas we assume there are no interactions between the atoms or molecules. Why is this a good assumption? Atoms or molecules in the gaseous state at room conditions are too far apart for IMF’s to operate. IMF’s are short range attractive forces. Attractive forces become important at low temperatures or high pressures. WHY?

  18. Some review questions • If a gas is compressed to high pressures, it will liquefy. Why? Click here for Chime structures to address the next two questions. • What holds a protein in the alpha-helix form? 3. How about a beta-sheet protein?

  19. LESSON LEARNEDAll of biologyis held togetherby chemistry! Go tell a biologist!!!!

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