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Intermolecular Forces

Intermolecular Forces. What is the difference?. What is the difference between: INTER INTRA Inter-molecular are forces between molecules and intra are forces within a molecule. These are the forces that hold our world together!. Intermolecular Forces (IMF).

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Intermolecular Forces

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  1. Intermolecular Forces

  2. What is the difference? What is the difference between: INTER INTRA Inter-molecular are forces between molecules and intra are forces within a molecule. These are the forces that hold our world together!

  3. Intermolecular Forces (IMF) IMFs can be used to determine characteristics of a substance including the state of matter.

  4. Intermolecular Forces (IMF) • Macro-covalent • Metallic • Hydrogen • Ionic • Dipole-Dipole • Dispersion

  5. 1. Macro-Covalent • The strongest of them all. • Examples: Diamond (all Carbon atoms) Rocks (Silicon and Oxygen) • Held together by covalent bonds • Hard, high melting point • Poor conductor of heat and electricity • Solids

  6. carbon atoms 1. Macro-Covalent Allotropes: diamond graphite

  7. Crystalline quartz (SiO2) Non-crystalline quartz glass

  8. 2. Metallic Solids at room temperature STRONG Intermolecular Forces Metal Atoms give up electrons This creates many dipoles throughout the atoms, they SHIFT but are always there “SEA of electrons”

  9. 3. Hydrogen Bonding A strong intermolecular attractions Caused by very strong dipole-dipole attraction between molecules with N-H, O-H, and F-H bonds. Responsible for many of water’s special properties. Liquids

  10. 3. Hydrogen Bonding

  11. or … … H H B A A A 3. Hydrogen Bonding The hydrogen bond is a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. IT IS NOT A BOND. A & B are N, O, or F

  12. 4. Ionic Very strong Permanent strong charge interactions Usually crystal in formation (solids) Very high melting points

  13. 5. Dipole-Dipole Caused by attraction of positive end of one polar molecule to negative of another polar molecule.

  14. Molecular Polarity In order for a molecule to be polar it must have polar bonds and be asymmetrical in shape. Lone pairs always lead to asymmetry. Linear, trigonal planar, and tetrahedral are symmetrical shapes and dipoles will cancel if all bonds are equal.

  15. Orientation of Polar Molecules 5. Dipole-Dipole Attractive forces between polar molecules Liquids

  16. 6. London Dispersion Forces Get stronger with increase in mass Gas Only attractive force between non-polar molecules (symmetrical or those with only non-polar bonds) or single atoms.

  17. 6. London Dispersion Forces Momentary Dipole

  18. Practice – Write phase and IMF for each H2O CCl4 CH2O NH3 Hg MgCl2

  19. Practice – Write phase and IMF for each H2O – Hydrogen Bonding - Liquid CCl4 – London Dispersion Forces - Gas CH2O – Dipole-dipole forces - liquid NH3 – Hydrogen Bonding - Liquid Hg – Metallic - Solid MgCl2 – Ionic - Solid

  20. Homework • WS 8.4 • Check webgrader • If I don’t have it by Friday it will not go in your grade

  21. Wednesday 4/11 and Thursday 4/12

  22. Physical Properties Affected by IMFs Surface Tension Volatility Capillarity Solubility “Like dissolves like” Boiling and Melting Point

  23. Affects of Intermolecular Forces Volatility Ability to evaporate • High when attractions are weak. Why? Compare volatility of alcohol and water. Capillarity Ability to climb up a tube or surface • High when liquid molecules are attracted to the tube or surface. Ex. Meniscus, paper towels, blood test

  24. Capillary Action

  25. Solubility How does a snow globe work?

  26. Solubility What dissolves in what? • Ionic substances dissolve in water • Covalent compounds: A. Non-polar dissolves in non-polar solvents. B. Polar solutes dissolve in polar solvents. C. Partially polar (only polar in a small part of the molecule) solutes dissolve in partially polar solvents. Like Dissolves Like!

  27. Basilisk Lizard

  28. Surface Tension A “skin” develops on the surface of liquids. Water’s is very strong. • High when molecules are attracted to each other cohesion. Ex. Paper clip “floating” Water striders

  29. Surfactants • Molecules that act to disrupt a liquid’s surface tension “wetting agent” • Structure-long non-polar hydrocarbon tail and a polar or ionic head

  30. How do they work? • Disrupt surface tension by acting like a “wedge”

  31. Surfactants as Cleaning Agents • Non-polar hydrophobic (water-hating) tails and polar or ionic hydrophilic (water-loving) heads form micelles.

  32. The solute and the solvent have to be attracted to each other in order to dissolve. Ionic solid dissolving in water

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