Review IM Forces

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Review IM Forces

• Section 10.1

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Forces Between Particles in Solids and Liquids

• Ionic compounds
• Attractive forces between oppositely charged ions
  hold ionic compounds together.
• Ionic bonds are the strongest interparticle
  force.
• Smaller the ion and the larger the charge on the
  ion the stronger the ionic bond

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Forces Between Particles in Solids and Liquids

• Molecular compounds
• Intermolecular (IM) forces between molecules
  attract molecules to each other in the liquid and
  solid state.
• IM forces are very weak as compared to ionic or
  covalent bonds

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IM Forces

• Three types of IM Forces
• Dipole-dipole force
• Hydrogen bonding
• London dispersion forces
• See pages 426-428

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Interparticle Forces and Physical Properties

• The stronger the attractive forces between
  particles in a liquid or solid, the
• Higher the
• Melting point
• Boiling point
• Surface tension
• Viscosity
• Lower the
• Vapor pressure

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IM Forces

• Dipole-dipole forces
• Attractive forces between oppositely charged
  dipoles.
• Dipole-dipole forces are found between polar
  compounds.
• The more polar the compound the stronger the
  dipole-dipole force.

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IM Forces

• Hydrogen bonds
• Attractive force between a d H bonded to an O,
  N, or F and a d- O, N, or F on another molecule.
• Really a relatively strong dipole-dipole force

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Hydrogen Bonding

• Hydrogen bonding is the strongest of the IM
  forces.
• H bonding is very important in water and in many
  biological molecules.

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London Dispersion Forces

• London Dispersion force
• Very weak and short-lasting attractive forces
  between temporary dipoles
• See figure 10.5
• Weakest of the IM forces

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London Dispersion Forces

• London Dispersion forces
• Found between all molecules in liquid/solid
  state.
• Of greatest significance in nonpolar molecules as
  its the only IM force between nonpolar molecules
• The larger the molecule the stronger the
  dipersion forces.

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Interparticle Forces

• Weakest London dispersion forces
• Dipole-dipole force
• Hydrogen Bonding
• Strongest Ionic bond

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CH 11 Properties of Solutions

• Describing Solutions concentration units
• Energetics of solution formation
• Colligative Properties of solutions
• BP elevation
• FP depression
• Osmotic pressure
• Vapor Pressure

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Terms

• Solution homogeneous mixture
• Solvent generally the larger component of the
  solution
• Determines the physical state of the solution
• Solute generally the smaller component of the
  solution
• Solute is dispersed in the solvent

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Solution Composition

• Concentrated solution
• Dilute solution

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Solution Composition

• Unsaturated solution
• Saturated solution
• Supersaturated solution

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Concentration Units

• Molarity (M) moles solute/Liters solution
• Mass Mass solute/mass solution x100
• Mole fraction (cA) moles A/total moles
• Molality (m) moles solute/kg solvent

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Practice!
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Solution Formation

• Formation of a solution involves 3 steps
• Separate the solute particles
• expand the solute
• Separate the solvent particles
• Expand the solvent
• Form the solution
• Solute and solvent interact

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Solution Formation

• Each step of solution formation involves energy
  and has a DH.
• DH1 energy needed to separate the
  solute
• DH2 energy needed to separate the
  solvent
• DH3 energy released when solution
  forms

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Solution Formation

• DHsolution DH1 DH2 DH3
• Solutions form when the DHsolution is a small
  value see page 492

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Factors Impacting Solubility

• Structure like dissolves like
• 38 on page 520

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Factors Impacting Solubility

• Pressure
• Pressure has little impact on the solubility of
  liquids and solids
• Pressure has a significant impact on the
  solubility of gases in a liquid
• The higher the pressure of gaseous solute above a
  liquid the higher the concentration of the gas in
  the solution

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• Henrys Law C kP
• No calculations required.
• Page 494

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Temperature and Solubility

• Temperature has variable effects on the amount of
  solid that will dissolve in an aqueous solution!
• See figure 11.6 page 496
• Solutes do dissolve more rapidly at higher
  temperatures

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Temperature and Solubility

• The solubility of a gas in water decreases as
  temperature increases.
• See figure 11.7 on page 496
• Thermal pollution read the story on page 497
  when you get a chance

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Vapor Pressure of Solutions

• See Raoults Law on page 498
• Psolution csolvent P0 solvent

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Colligative Properties

• Colligative properties
• properties of a solution that depend upon the
  amount of dissolved solute, not the identity of
  the solute.
• Freezing point depression
• Boiling point elevation
• Osmotic Pressure
• Note I will be weaving section 11.7 and the
  vant Hoff factor (i) into my consideration of
  these properties and not consider it separately.

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Colligative Properties

• FP Kf m i
• BP Kb m i
• See page 505 for needed constants

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1. Calculating the bp or fp of a solution
2. Calculating the molar mass of a solute from fp or
   bp data

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Osmotic Pressure

• Osmotic Pressure (P) is often used to determine
  the molar mass of large biological molecules
• See figure 11.17 on page 508
• P MRTi