intermolecular forces. kinetic molecular theory describes the behavior of subatomic particles...
TRANSCRIPT
Intermolecular ForcesIntermolecular Forces
Kinetic Molecular TheoryKinetic Molecular Theory
Describes the behavior of subatomic particles• Liquids, solids, and gases are composed of
small particles that have mass. • Particles are in constant, random, rapid motion.• Particles have collisions. • Particles have an avg. KE directly related to
temperature.• The state of a substance at room temperature
depends on the strength of the attractions between its particles.
Definition of IMFDefinition of IMF
Attractive forces between molecules.
Much weaker than chemical bonds within molecules.
Definition of IMFDefinition of IMF
Intramolecular forces:
Covalent Bonding
Much stronger than chemical bonds between atoms.
Examples : nonpolar, polar sharing
Definition of IMFDefinition of IMF
Intermolecular ForcesAttractive forces between molecules.
Much weaker than chemical bonds within molecules.
Intermolecular ForcesIntermolecular Forces
Attractive forces between molecules or particles (ions, metal atoms, etc…)
Examples:
dispersion, (London /Vander Waals); dipole-dipole, dipole-ion, hydrogen “bonding”, metallic bonding, ion-ion
Intermolecular ForcesIntermolecular Forces
Relative Strength:
Examples:
dispersion, (London /Vander Waals); dipole-dipole, dipole-ion, hydrogen “bonding”, metallic bonding, ion-ion
Weakest
Strongest
Types of IMFTypes of IMF
Types of IMFTypes of IMF
London Dispersion Forces
View animation online.
Types of IMFTypes of IMF
Dipole-Dipole Forces
+ -
View animation online.
Types of IMFTypes of IMF
Hydrogen Bonding
Determining IMFDetermining IMF
NCl3• polar = dispersion, dipole-dipole
CH4
• nonpolar = dispersionHF
• H-F bond = dispersion, dipole-dipole, hydrogen bonding
Physical PropertiesPhysical Properties
Liquids & SolidsLiquids & SolidsLiquids & SolidsLiquids & Solids
Liquids vs. SolidsLiquids vs. Solids
LIQUIDS
Stronger than in gases
Y
high
N
slower than in gases
SOLIDS
Very strong
N
high
N
extremely slow
IMF Strength
Fluid
Density
Compressible
Diffusion
Liquid PropertiesLiquid Properties
Surface Tension• attractive force between particles in a
liquid that minimizes surface area
Liquid PropertiesLiquid Properties
Capillary Action• attractive force between the surface of
a liquid and the surface of a solid
water mercury
Types of SolidsTypes of Solids
Crystalline - repeating geometric pattern• covalent network• metallic• ionic• covalent molecular
Amorphous - no geometric pattern
decreasingm.p.
Types of SolidsTypes of Solids
Ionic(NaCl)
Metallic
Types of SolidsTypes of Solids
CovalentMolecular
(H2O)
CovalentNetwork
(SiO2 - quartz)
Amorphous(SiO2 - glass)
Liquids & SolidsLiquids & SolidsLiquids & SolidsLiquids & Solids
Changes of StateChanges of State
Phase ChangesPhase Changes
Phase ChangesPhase Changes
EvaporationEvaporation• molecules at the surface gain enough
energy to overcome IMF
VolatilityVolatility• measure of evaporation rate• depends on temp & IMF
Phase ChangesPhase Changes
Kinetic Energy
# o
f P
art
icle
s
p. 477
Boltzmann Distribution
temp
volatility
IMF
volatility
Phase ChangesPhase Changes
EquilibriumEquilibrium• trapped molecules reach a balance
between evaporation & condensation
Phase ChangesPhase Changes
Vapor PressureVapor Pressure• pressure of vapor above
a liquid at equilibrium
IMF v.p.temp v.p.
• depends on temp & IMF• directly related to volatility
p.478
temp
v.p
.
Phase ChangesPhase Changes
Boiling Point• temp at which v.p. of liquid
equals external pressure
IMF b.p.Patm b.p.
• depends on Patm & IMF
• Normal B.P. - b.p. at 1 atm
Which has a higher m.p.?• polar or nonpolar?• covalent or ionic?
Phase ChangesPhase Changes
Melting Point• equal to freezing point
polar
ionic
IMF m.p.
Phase ChangesPhase Changes
Sublimation
• solid gas
• v.p. of solid equals external pressure
EX: dry ice, mothballs, solid air fresheners
Heating CurvesHeating Curves
Melting - PE
Solid - KE
Liquid - KE
Boiling - PE
Gas - KE
Heating CurvesHeating Curves
Temperature Change• change in KE (molecular motion) • depends on heat capacity
Heat Capacity• energy required to raise the temp of 1
gram of a substance by 1°C• “Volcano” clip - water has a very high
heat capacity
Heating CurvesHeating Curves
Phase Change• change in PE (molecular arrangement)• temp remains constant
Heat of Fusion (Hfus)
• energy required to melt 1 gram of a substance at its m.p.
Heating CurvesHeating Curves
Heat of Vaporization (Hvap)
• energy required to boil 1 gram of a substance at its b.p.
• usually larger than Hfus…why?
EX: sweating, steam burns, the drinking bird
Phase DiagramsPhase Diagrams
Show the phases of a substance at different temps and pressures.