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Giant Covalent Molecules

Giant Covalent Molecules. Covalent Bonds. Simple molecular structure ex: CH 4. Giant covalent structure ex: diamonds. - strong forces between atoms (within molecule) - weak forces between molecules. covalent bond between atoms or molecules. depend on the polarity of the molecules.

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Giant Covalent Molecules

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  1. Giant Covalent Molecules

  2. Covalent Bonds Simple molecular structure ex: CH4 Giant covalent structure ex: diamonds -strong forces between atoms (within molecule) -weak forces between molecules covalent bond between atoms or molecules depend on the polarity of the molecules

  3. sometimes, a solid lattice is held together with covalent bonds • giant covalent structures: very hard, very high melting/boiling points • Ex.: diamonds and graphite (both C), SiO2 (crystals)

  4. Intermolecular Forces IMF

  5. IMF: Forces (not bonds) that hold covalent molecules together • For solids and liquids

  6. IMF control the physical properties of covalent compounds. • Melting and boiling point • Viscosity (how thick/sticky a liquid is) • Solubility (what will dissolve in a liquid) • IMF explains why WATER is the liquid required for life!

  7. Three types of IMF Increasing strength • Van der Waal’s • Dipole-dipole • Hydrogen bonds

  8. 1. van der Waal’s Forces • Between non-polar molecules • Electrons move randomly, so by chance, many e- can end up at one end of a molecule • “temporary dipole” • even in non-polar molecules! • Ex: CCl4

  9. This repels (pushes away) the electrons of nearby molecules • Temporary dipoles do not last because the e- are constantly moving.

  10. vdW Force depends on: • surface area of molecules • molar mass of molecules

  11. 2. Dipole-dipole Forces • Between polar molecules • Because of the electrostatic attraction between molecules • opposite charges attract one another

  12. stronger than vdW Forces • Ex: HCCl3

  13. Affect the boiling point of a substance

  14. 3. Hydrogen Bonding • Between polar molecules that have H and one of N, O or F • H-bonds are the attraction between a non-bonding e- pair on N, O or F and the H atom. • N, O or F has a slight negative charge, H has a slight positive charge.

  15. H-bond is the strongest IMF • H-bonds affect the physical properties of substances (ex: boiling point) • Ex: H2O

  16. H-bonds cause: • higher boiling point, lower volatility • volatility: how easily something evaporates • greater solubility in water • higher viscosity • viscosity: resistance to flow, “thickness”

  17. All IMF affect the properties of a substance. • The stronger the IMF, the… • Higher the boiling point • Higher the melting point • Greater the viscosity (resistance to flow) • IMF also affect the solubility of a substance

  18. http://www.youtube.com/watch?v=cgiNk94XyaI

  19. Practice Quiz on Thursday • I will give you the formula for a molecule. You need to provide the: • Lewis structure • Molecule shape/VSEPR Theory • Polarity • Intermolecular Force present • Also, know something about giant covalent structures

  20. Example Quiz Question: • For the molecule HCCl3: • Draw the Lewis Structure • Draw the shape including the bond angle, and label it with the name of the shape. • Identify polarity using delta + and delta – • Label the molecule as Polar or Non-polar. • What kind of intermolecular forces would exist between molecules of this compound?

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