Chapter 12: Liquids, Solids and Interparticle Forces

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Chapter 12 Liquids, Solids and Interparticle
Forces
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What is a liquid? A solid?

• Properties of liquids and solids depend on
  Interparticle (Intermolecular) forces
• - vaporization/condensation/freezing
• - equilibrium vapor pressure/volatility
• - surface tension
• - boiling point/freezing point
• We are going to learn about Interparticle or
  Intermolecular forces first!

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TYPES OF INTERPARTICLE FORCES - SEE HANDOUT

• All forces of attraction between atoms, ions,
  molecules are Interparticle forces
• Includes ionic bonding, covalent bonding,
  metallic bonding, and ion-dipole attraction
• Important Subcategory is Intermolecular Forces
• Also called Van Der Waals forces
• Weak to moderate forces of attraction
• Not a type of bonding
• Includes three main ones London Dispersion
  Forces, Dipole-dipole Attraction and Hydrogen
  Bonding Attraction

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Intermolecular Forces

• 1. London dispersion forces (LDF)
• - Small to moderate strength
• - Depend on size of electron cloud (and so also
  molar mass) of atom or molecule
• - Noble gases, diatomic elements, and many other
  nonpolar compounds

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Nonpolar molecules such as H2 can develop
instantaneous dipoles and induced dipoles. The
attractions between such dipoles, even through
they are transitory, create London dispersion
forces. (See figures 12.17 18)
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Table 12.4 Dispersion Force and Molar Mass
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(No Transcript)
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Intermolecular Forces

• 2. Dipole-dipole attraction
• - Moderate strength
• - Molecules that have polar covalent bonds
• - Polar molecules d and d- attraction
• Table of Properties of Hydrohalogens
• H-F H-Cl H-Br H-I
• DEN 1.4 1.1 0.8 0.4
• e-s 10 18 36 54
• BP 291 188 206 238

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There are many dipole-dipole interactions
possible between randomly arranged ClF molecules.
In each interaction, the positive end of one
molecule is attracted to the negative end of a
neighboring ClF molecule.
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Polarity and Dipole-to-Dipole Attraction
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Intermolecular Forces

• 3. Hydrogen-bonding (enhanced dipole-dipole)
• - Strong force, but much less than real bonding
• - Memory helper E.T. FON Home only F-H, O-H
  and N-H have this type of force
• - Due to small radius and high EN
• - See in boiling point data

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Depiction of hydrogen bonding among water
molecules. The dotted lines are the hydrogen
bonds.
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Figures 12.22 24 Intermolecular H-Bonding
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Hydrogen Bonding and Water

• Water - 80 hydrogen-bonded - very tight
  arrangement (also high viscosity high density and
  high specific heat)
• Ice - crystal is very open, less dense than
  liquid
• (4. Dipole - induced dipole between diff types
  of molecules, O2 in H2O)

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Diagrams of hydrogen bonding involving selected
simple molecules. The solid lines represent
covalent bonds the dotted lines represent
hydrogen bonds.
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If there were no hydrogen bonding between water
molecules, the boiling point of water would be
approximately - 80C.
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Notice that molecules with F-H, O-H and N-H have
HIGH BPs because of Hydrogen-bonding forces of
attraction.
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Properties and H-Bonding
Name Form- ula Molar Mass Structure BP, C MP, C Solb in Water
Ethane C2H6 30.0 -88 -172 immisc
Methanol CH3OH 32.0 64.7 -97.8 misc- ble
Table on page 411 in Tro.
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Chemistry at a GlanceIntermolecular Forces
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PRACTICE IDENTIFYING THE TYPE OF IM FORCE

• CH4(g) C6H6(l)
• Br2(l) HBr(l)
• IBr(s) CH3OH(l)

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There are six changes of state possible for
substances learn all 6
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Distinguishing Properties of Solids, Liquids, and
Gases
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BP, FP, Phase Changes, and DHophase

• Boiling point temperature at which the vapor
  pressure of a liquid is equal to the external
  pressure above the liquid, usually atmospheric
  pressure of 1 atm
• Freezing point temperature at which a liquid
  changes into a solid at 1 atm

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BP, FP, Phase Changes, and DHophase

• Phase changes changes of state
• Learn all six
• Accompanied by heat flow called Enthalpy of phase
  change or DHophase
• Heat of vaporization liquid to vapor energy (J)
  to vaporize 1 mol at constant T P
• Heat of fusion solid to liquid energy (J) to
  melt 1 mol at constant T P

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BP, FP, Phase Changes, and DHophase

• Sensible heat transfer temperature is changed
  but not phase
• q m cp DT
• m is mass, cp is specific heat and DT is Tf Ti
• See example (13.1)
• Latent heat transfer using DHophase phase
  changes but not temperature
• q m DHophase
• m is mass or moles depending on units
• See example (13.2)

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BP, FP, Phase Changes, and DHophase

• Specific heat energy required to raise
  temperature of 1.00 gram of substance by 1.00oC
• cp for water is 4.184 J/g.oC

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In the evaporation of a liquid in a closed
container (a), the liquid level drops for a time
(b) and then becomes constant (ceases to drop).
At that point a state of equilibrium has been
reached in which the rate of evaporation equals
the rate of condensation (c).
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Equilibrium Vapor Pressure

• In closed system at any given temperature,
• rate of vaporization rate of condensation
• At dynamic equilibrium means number of molecules
  in gas phase and number of molecules in liquid
  phase stay the same, but processes still
  happening
• Vapor pressure taken at equilibrium the partial
  pressure
• Vapor pressure changes with change in temperature
  (listen to weather)
• Plot as vapor pressure curves pressure vs.
  temperature (see Fig 13.6)
• Boiling point anywhere along curve see bubbles
  rise to surface
• Normal boiling point is when vapor pressure is
  1.00 atm or 760. Torr

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Vapor Pressure of Water at Various Temperatures.
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Boiling Point of Water at Various Locations That
Differ in Elevation
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• Just read about surface tension and capillary
  action
• Just read section (13.10 and skip section
  13.11