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Ch. 10: Liquids and Solids

Ch. 10: Liquids and Solids. 10.1 Intermolecular Forces Read this section!!! Students frequently get confused and they like to ask about this topic on the AP Exam!!!. Intra- vs. Inter-. intramolecular forces inside molecules hold atoms together in a molecule intermolecular forces

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Ch. 10: Liquids and Solids

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  1. Ch. 10: Liquids and Solids 10.1 Intermolecular Forces Read this section!!! Students frequently get confused and they like to ask about this topic on the AP Exam!!!

  2. Intra- vs. Inter- • intramolecular forces • inside molecules • hold atoms together in a molecule • intermolecular forces • between different molecules • get weaker as phase changes from S – L – G • When a substance changes state, molecule stays together but intermolecular forces weaken

  3. Examples • Intramolecular Forces • Covalent Bonding • Ionic Bonding • Metallic Bonding • MUCH STRONGER • Intermolecular Forces – only occur between different molecules • Dipole-Dipole Interactions • Hydrogen Bonding • London Dispersion Forces • MUCH WEAKER

  4. Dipole-Dipole Attraction • when molecules with dipole moments line up to minimize repulsion and maximize attraction • very weak compared to covalent and ionic bonds

  5. Hydrogen Bonding • happens between H and N, O, or F • very strong type of dipole-dipole attraction • because bond is so polar • because atoms are so small

  6. London Dispersion Forces • in every molecular compound • only important for nonpolar molecules and noble gas atoms • weak, short-lived • caused by formation of temporary dipole moments

  7. Intermolecular Forces • Strongest  H bonding • Next Strongest  Dipole-Dipole • Weakest  London Dispersion • Why important?? Influences boiling points, melting points, etc….

  8. Figure 10.4 The Boiling Points of the Covalent Hydrides of the Elements in Groups 4A, 5A, 6A, and 7A

  9. Practice • which has highest boiling pt? • HF, HCl, or HBr? (H-Bonding) • Identify the most important Forces : • BaSO4 • H2S • Xe • C2H6 • P4 • H2O • CsI ionic dipole-dipole H-bonding London Dispersion

  10. CO2 or OCS CO2: nonpolar so only LD OCS: polar so dipole-dipole PF3 or PF5 PF3: polar so dipole-dipole PF5: nonpolar so only LD SF2 or SF6 SF2: polar so dipole-dipole SF6: nonpolar so only LD SO3 or SO2 SO3: nonpolar so LD only SO2: polar so dipol-dipole Which has stronger IMF’s?

  11. Ch. 10: Liquids and Solids 10.2 Liquids

  12. Properties of Liquids • low compressibility • no rigidity • high density compared to gases • beads up as droplets • molecules on surface are subject to attractions from side and below • surface tension • resistance to an increase in surface area • greater tension means stronger IMF’s

  13. Properties of Liquids • capillary action • spontaneous rising of a liquid up a tube • from cohesive forces (IMF’s) and adhesive forces (between liquid and container) • viscosity • measure of a liquid’s resistance to flow • strong IMF’s  highly viscous • large, complex molecules  highly viscous

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