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. giant covalent structures: very hard, very high melting/boiling points
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 Van der Waal’s Dipole-dipole Hydrogen bonds
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.

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

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

14. stronger than vdW Forces
Ex: HCCl3

15. Affect the boiling point of a substance

16. 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.

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

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

20. 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

25. 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

26. 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?