IMF

Tref - normal freezing point pulling energy out of the system Attractive forces win and lock the molecules into crystal structure mental boiling etc pumps energy back in

• endothermic processes
• need to have enough energy to ignore neighbors and not form bonds
• ice → steam most of the energy goes into vaporization
  • Melting takes less energy than vaporizing
• liquid to vapor completely breaks all of the forces
• Water moleculesa re extremely sticky
• Types of bonds
  • Nonpolar molecules: london dispersion forces
    • Weakest, but present in everything
    • Electrons arent static, they zip around creating a temporary dipole as they interact with each other
      • Temporary static cling
    • The scale of it scales with polarizability. The bigger the atom, the bigger electron cloud
    • Cl2 and I2, I2 is bigger so it forms a solid
      • Temporary LDFs are strong enoigh to form it into a solid
      • Surface area is also important - structural isomer comparison
    • Straight chain vs bent chain, higher surface area means it has more spots to interact with its neighbors
      • Pentane is liquid at room temperature while propane is a gas
      • LDFs are strong enough to keep it a liquid
  • Dipole-Dipole forces
    • You can get a permanent dipole through polar shapes
    • Aceton and Butane, almost same molar mass
      • Acetone is polar while Butane is non polar
        • Functional group makes it very polar and permanent dipole
      • Polar molecules are “stickier”, the attraction is always on
  • Strongest non-bonding force is Ion Dipole forces
    • Full ion interacts with a molecule like water
      • Full charge, not a partial one
  • Hydrogen bond
    • Incredibly strong type of dipole-dipole force
    • Very specific, hydrogen atom that is covalently bonded to N,O,F
      • These three are so electronegative that they pull the electron cloud away from the hydrogen
      • Very concentrated charge
    • Trend based on size is broken once the hydrogen bonds break
      • That’s where most of the enrgy in breaking water goes
  • If you see CH4, it isn’t a hydrogen bond because there is no N,O,F, it is just a LDF
• Vapor Pressure
  • Liquids ina sealed container have an inverse relationship
  • Stronger IMF means lower vapor pressure
  • As long as there is liquid in the flask, the vapor pressure stays the same
    • Dynamic equilibrium
    • System self corrects to maintain constant pressure determined by the substance
• Metals have sea of electrons where the outer ones are delocalized
  • Make it a conductor
• Solid is usually denser than liquid, except for water where ice is less dense than liquid
• If H bonding is what gives water its high boiling point, how does that same hydrogen bond network, when it freezes into ice, force the molecules to become farther apart in a liquid