Ch.10

10.1 Intermolecular Forces

Key Concepts:

• Intermolecular Forces (IMFs) = attractions between molecules (vs. intramolecular = within a molecule).
  
  

• Stronger IMFs → higher melting/boiling points, surface tension, viscosity.
  
  

Types of IMFs:

1. Dispersion Forces (London Forces)
   
   

   • Present in all molecules (polar & nonpolar).
     
     

   • Caused by temporary dipoles from electron movement.
     
     

   • ↑ Molar mass & size → ↑ dispersion forces.
     
     

   • ↑ Polarizability = ↑ strength (e.g., I₂ > F₂).
     
     

2. Dipole-Dipole Interactions
   
   

   • Occur between polar molecules.
     
     

   • Attraction between δ⁺ and δ⁻ ends of molecules.
     
     

   • Stronger than dispersion (for similar-sized molecules).
     
     

3. Hydrogen Bonding
   
   

   • Strongest IMF (but still weaker than covalent).
     
     

   • Occurs when H is bonded to N, O, or F.
     
     

   • Explains high boiling points of H₂O, NH₃, HF.
     
     

   • Very polar + small atoms = strong H-bonds.
     
     

10.2 Properties of Liquids

Viscosity

• Resistance to flow.
  
  

• ↑ IMFs → ↑ viscosity (e.g., honey).
  
  

• ↑ Temp → ↓ viscosity.
  
  

Surface Tension

• Energy required to increase surface area.
  
  

• Caused by cohesive forces.
  
  

• Water has high surface tension due to H-bonding.
  
  

Capillary Action

• Liquid rises/falls in a narrow tube.
  
  

• Adhesive (liquid to surface) and cohesive (liquid to itself) forces.
  
  

• Water rises in glass (concave meniscus); mercury does not (convex).
  
  

10.3 Phase Transitions

Definitions:

• Boiling Point: vapor pressure = atmospheric pressure.
  
  

• Melting/Freezing Point: solid ↔ liquid equilibrium.
  
  

• Sublimation: solid → gas.
  
  

• Deposition: gas → solid.
  
  

Vapor Pressure

• Pressure exerted by vapor in equilibrium with liquid.
  
  

• ↑ Temp → ↑ vapor pressure.
  
  

• Weaker IMFs = higher vapor pressure (e.g., diethyl ether > ethanol).
  
  

10.4 Phase Diagrams

Show phase (solid/liquid/gas) at different T and P.

Triple point: all 3 phases in equilibrium.

Critical point: beyond this, liquid/gas are indistinguishable (supercritical fluid).

For water, melting curve has negative slope (unusual).

10.5 Solids

Types of Solids:

10.6 Lattice Structures in Crystalline Solids

Unit Cells

• Simple Cubic (SC):
  
  

  • 1 atom/unit cell, coord. # = 6, 52% packing.
    
    

  • Rare (e.g., Po).
    
    

• Body-Centered Cubic (BCC):
  
  

  • 2 atoms/unit cell, coord. # = 8, 68% packing.
    
    

  • e.g., Fe, Cr, K.
    
    

• Face-Centered Cubic (FCC/CCP):
  
  

  • 4 atoms/unit cell, coord. # = 12, 74% packing.
    
    

  • e.g., Cu, Al, Ag.
    
    

• Hexagonal Closest Packing (HCP):
  
  

  • Coord. # = 12, also 74% packing.
    
    

  • e.g., Mg, Zn.
    
    

Packing Efficiency

SC < BCC < FCC ≈ HCP