Liquids and Solids

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Chapter 13

• Liquids and Solids

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Compare and Contrast Gases, Liquids and Solids

• Water vapor at 1 atm, temp 20 ?C, and amount if
  1 mol. What is its volume?
• What is the volume of 1 mol of liquid water at 20
  ?C?
• That is 1300x smaller than the volume occupied by
  the same number of molecules (6.0233 x 1023) in
  the gas phase.

3
Homework Problems

• 8, 16, 18, 22, 30, 38, 46, 56, 70, and 74.

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Intermolecular Forces

• The physical state of a substance at a given
  temperature and pressure is related to several
  factors, which involve intermolecular forces.
• Particles with greater mass have a greater
  attraction for each other.
• The boiling points and melting points of
  substances increase with greater molecular mass.

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Forces Between Particles

• Interionic Forces attractive forces between
  ions, and these are some of the strongest forces.
• They are due to the attraction of opposite
  charges.
• Examples Na Cl- Ca2 O2- Al3 N3-

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Forces Between Particles

• Intramolecular Forces. Forces that hold atoms
  together within molecules. Polar and non-polar
  covalent bonds.
• Examples H-O-H CO
• Intermolecular Forces. The attractive force
  between molecules. These forces are weaker than
  interionic or intramolecular forces. These
  forces help determine the physical properties of
  molecular compounds.
• Also called van der Waals forces

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Intermolecular Forces

• Dipole Forces Polar molecules are attracted to
  each other via the negative end of one molecule
  being attracted to the positive end of another
  molecule.

Liquid
Solid
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Intermolecular Forces

• Hydrogen Bond Bond between hydrogen attached to
  an electronegative atom (F, O, or N) to another
  electronegative atom.

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Dispersion Forces

• (London Forces) between nonpolar molecules.
• Examples H2 Br2

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Intermolecular Forces

• Listed from strongest to weakest
• Hydrogen bondsgtDipole forcesgtDispersion forces.

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Substances With Stronger Intermolecular Bonds,
Generally Have a

• Lower Vapor Pressure
• Higher Boiling Point
• Higher Melting Point
• Greater Viscosity
• Greater Surface Tension

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The Liquid State

• Viscosity A measure of the resistance of a
  liquid to flow.
• Depends on the size of the molecule.
• Type of attractive forces.
• Viscosity decreases with increasing temperature.

13
Properties of Liquids

• Surface Tension resistance of a liquid surface
  to penetration by a solid object.
• Explains formation of droplets on solid surface.
• Surfactants reduce surface tension.

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Vaporization and Condensation

• Evaporation transformation from liquid to vapor
  (gas phase).
• Condensation conversion from vapor to liquid.
• There is an equilibrium between the two phases
• Liquid Vapor

Vaporization
Condensation
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Boiling Point

• BP is the temperature at which the vapor pressure
  of a liquid equals the external pressure
  (atmospheric).

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Distillation

• A volatile component can be separated from a
  non-volatile component by distillation. The
  volatile component is evaporated and the vapors
  are condensed, leaving the non-volatile component
  behind.

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Distillation Apparatus
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Heat of Vaporization

• Heat is required to vaporize a liquid.
• A liquid that evaporates at room temperature
  absorbs heat from the surroundings.
• The quantity of heat required to vaporize 1 mol
  of liquid is called the molar heat of
  vaporization.

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The Solid State

• Many solids are amorphous. The particles (ions or
  molecules) have no definite order.
• Examples are glass, rubber, and plastic.
• Crystalline solids have a regular arrangement of
  particles, called a crystal lattice.
• Some types of crystal lattice are
• simple cubic
• body-centered cubic
• face-centered cubic

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Common Crystal Lattices
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Solids may be classified by the type of
inter-particle force.

• Ionic solids Ions are at each lattice point in
  the crystal.
• Molecular solids Have discrete molecules at each
  lattice point. Held together by intermolecular
  forces.
• Covalent network or macromolecular solids have
  atoms at the lattice points. They are held
  together by covalent bonds. Examples are SiC,
  graphite and diamond.

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Allotropes

• Carbon and other elements can exist in various
  forms. These forms are called allotropes.
• Allotropes of carbon are graphite, amorphous, and
  diamond, and nanotubes. These are
  macromolecular.
• A molecular allotrope is Buckminsterfulleranes.

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• The Structure of Diamond, an Allotrope of Carbon

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Graphite, an Allotrope of Carbon
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Buckminsterfullerene, an Allotrope of Carbon
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Melting and Freezing

• When a crystalline solid is heated, particles
  vibrate more vigorously and become liquid.
• This process is called melting.
• When a substance changes from a liquid to a solid
  the process is called freezing.
• Liquids and solids are in dynamic equilibrium
• Solid Liquid

melting
freezing
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Heat of Fusion

• The amount of heat required to convert 1
  mol of a solid to a liquid is called the molar
  heat of fusion.

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Heating and Cooling Curves

• Specific heat capacity amount of heat needed to
  raise the temperature of 1 g of substance 1 ?C.

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Specific heat capacities
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Unique Properties of Water

• Ice is less dense than water
• Specific heat capacity is high
• Heat of vaporization is high
• Water as a universal solvent

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Solvent Properties of Water

• Highly polar, able to form hydrogen bonds.
• Good solvent for ionic compounds.
• Ion-dipole interaction

Insert figure 13.20