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Intermolecular Forces of Attraction

Intermolecular Forces of Attraction. IMFAs. Intermolecular Forces of Attraction Forces that exist between molecules By knowing the strengths of the IMFAs we can predict physical properties of molecules. The stronger the IMFAs, the more the molecules want to stick together.

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Intermolecular Forces of Attraction

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  1. Intermolecular Forces of Attraction

  2. IMFAs • Intermolecular Forces of Attraction • Forces that exist between molecules • By knowing the strengths of the IMFAs we can predict physical properties of molecules. • The stronger the IMFAs, the more the molecules want to stick together. • This affects Boiling & Freezing Points, Evaporation Rate, and Miscibility.

  3. Ion-Ion (Ionic Bonding) • Ionic Compounds are all Solids at RT. • This is because the attraction between ions within the compound is so strong – like a bunch of Magnets sticking together. • Ionic compounds tend to dissolve in Polar solvents

  4. Ion-Dipole • Charged ions are attracted to the opposite charge of a polar covalent molecule. • These are very similar to Ionic bonding. • These forces occur when an ion is Dissolved in a Polar liquid.

  5. Dipole-Dipole • Similar to ionic bonding, the Partial Charges of a Polar molecule line up with the opposite charge of another polar molecule. • Polar compounds will be Miscible in polar solvents.

  6. Hydrogen Bonding • Strong Dipole-Dipole force: • When H is in a polar molecule and bonded with: • Nitrogen • Oxygen • Fluorine • It produces a very strong dipole-dipole attraction between different molecules.

  7. H-Bonding (cont’d) • Because of hydrogen bonding, a very small & light molecule like Water (H2O) is a liquid while a Heavier compound, H2S, is a gas. • So, if the molecules are polar and hydrogen is having FON, then it will have hydrogen bonding.

  8. London Dispersion Forces • Nonpolar molecules cannot have any of the previously mentioned forces of attraction since they do not have any dipole Moment or Charge. • Instead, the only forces available to these compounds are induced Dipoles. • LDFs arise when the electrons of one molecule are Pushed away by the electrons of another molecule.

  9. LDFs (cont’d) • A whole bunch of molecules doing this together create Temporary dipoles in otherwise nonpolar molecules. • These are by far the Weakest of the intermolecular forces.

  10. LDFs (yet again) These are the only forces available to Noble Gases. These are the forces at work when we are able to Liquefy or Solidify them.

  11. LDFs (one last time) • All Molecules have LDFs in addition to any of the other forces already mentioned • Except Ionic Compounds since they have permanent poles already.

  12. Size and Weight • If the molecule is Big & Bulky, it’s going to get stuck on other molecules when it moves around – kind of like Spaghetti. • For this reason, big molecules, even when they are Nonpolar, tend to be liquids or solids. • If the molecule has some really heavy atoms in it, it’s going to need more energy to get it moving around.

  13. Strength of IMFAs • Ion-Ion • Ion-Dipole • H-Bonding • Dipole-Dipole • London Dispersion Forces • The stronger the IMFAs, the more likely a compound will be a solid or liquid.

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