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Ch. 12 – States of MatterCh. 12 – States of MatterCh. 12 – States of MatterCh. 12 – States of Matter
I. Intermolecular ForcesI. Intermolecular Forces
A. Definition of IMFA. Definition of IMF
Attractive forces between molecules.
Much weaker than chemical bonds within molecules.
a.k.a. van der Waals forces
C. Johannesson
B. Types of IMFB. Types of IMF
B. Types of IMFB. Types of IMF
London Dispersion Forces
View animation online.
B. Types of IMFB. Types of IMF
Dipole-Dipole Forces
+ -
View animation online.
B. Types of IMFB. Types of IMF
Hydrogen Bonding
C. Determining IMFC. Determining IMF
NCl3• polar = dispersion, dipole-dipole
CH4
• nonpolar = dispersionHF
• H-F bond = dispersion, dipole-dipole, hydrogen bonding
II. Physical PropertiesII. Physical Properties
Ch. 12 - Liquids & SolidsCh. 12 - Liquids & SolidsCh. 12 - Liquids & SolidsCh. 12 - Liquids & Solids
A. Liquids vs. SolidsA. Liquids 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
B. Liquid PropertiesB. Liquid Properties
Surface Tension• attractive force between particles in a
liquid that minimizes surface area
B. Liquid PropertiesB. Liquid Properties
Capillary Action• attractive force between the surface of
a liquid and the surface of a solid
B. Liquid PropertiesB. Liquid Properties
Viscosity• Measure of the resistance of a liquid to
flow
B. Liquid PropertiesB. Liquid Properties
Cohesion• Force of attraction between
identical moleculesAdhesion
• Force of attraction
between different
molecules water mercury
C. Types of SolidsC. Types of Solids
Crystalline - repeating geometric pattern• covalent network• metallic• ionic• covalent molecular
Amorphous - no geometric pattern
decreasingm.p.
C. Types of SolidsC. Types of Solids
Ionic(NaCl)
Metallic
C. Types of SolidsC. Types of Solids
CovalentMolecular
(H2O)
CovalentNetwork
(SiO2 - quartz)
Amorphous(SiO2 - glass)
C. Types of SolidsC. Types of Solids
Allotrope• In a covalent network, different forms in the same
state
Carbon
allotropeswater mercury
C. Types of SolidsC. Types of Solids
Amorphous Solid• No geometric pattern
water mercury
Ch. 12 - Liquids & SolidsCh. 12 - Liquids & SolidsCh. 12 - Liquids & SolidsCh. 12 - Liquids & Solids
III. Changes of StateIII. Changes of State
A. Phase ChangesA. Phase Changes
A. Phase ChangesA. Phase Changes
EvaporationEvaporation• molecules at the surface gain enough
energy to overcome IMF
VolatilityVolatility• measure of evaporation rate• depends on temp & IMF
A. Phase ChangesA. Phase Changes
Kinetic Energy
# o
f P
art
icle
s
Boltzmann Distribution
temp
volatility
IMF
volatility
A. Phase ChangesA. Phase Changes
EquilibriumEquilibrium• trapped molecules reach a balance
between evaporation & condensation
A. Phase ChangesA. Phase 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
temp
v.p
.
A. Phase ChangesA. Phase 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?
A. Phase ChangesA. Phase Changes
Melting Point• equal to freezing point
polar
ionic
IMF m.p.
A. Phase ChangesA. Phase Changes
Sublimation
• solid gas
• v.p. of solid equals external pressure
EX: dry ice, mothballs, solid air fresheners
B. Heating CurvesB. Heating Curves
Melting - PE
Solid - KE
Liquid - KE
Boiling - PE
Gas - KE
B. Heating CurvesB. Heating 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
B. Heating CurvesB. Heating 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.
B. Heating CurvesB. Heating Curves
Heat of Vaporization (Hvap)
• energy required to boil 1 gram of a substance at its b.p.
EX: sweating, steam burns, the drinking bird
C. Phase DiagramsC. Phase Diagrams
Show the phases of a substance at different temps and pressures.
The following slides… same information, different explanation and examples
Phase Changes
Why do liquids and solids form at all?
• KMT postulates– A gas is a collection of small particles traveling in
straight-line motion and obeying Newton's Laws. – The molecules in a gas occupy no volume. – Collisions between molecules are perfectly elastic
• no energy is gained or lost during the collision
– There are no attractive or repulsive forces between the molecules.
– Kinetic energy is proportional to temperatureX
What is a phase?• Region of matter that is:
– chemically uniform– physically distinct– mechanically separable.
• Often synonymous with (same meaning as) “state of matter”
Changing phases
Distinguish liquid vs. solid?
Properties of …• Gas phase
– Like/unlike soccer players on field
• Liquid phase– Like/unlike crowd at a rally– Like/unlike gases
• Solid phase– Like/unlike movie theatre
• Compare intermolecular interactions – gases vs. liquids vs. solids
Phases of matter
Add
mor
e en
ergy
Phase change vocabulary
Phase changes and IMF’s• As InterMolecular Forces increase, melting
and boiling temperatures _________? (increase or decrease)?
Metallic bonding
Network covalent bonding
Larger sphere, higher
melting point
Strength of interactions
• Which simulation has stronger intermolecular interactions? A or B– How do you know?
A BSame temperature
Ranking of intermolecular interactions • Water• Wood• Iron• Air• Gold• Mercury• Carbon dioxide• Oxygen• Gasoline• Lead
vs.
Why?
Why is water special?
• Periodic trends– Boiling and melting points of hydrides
KMT, energy and phase
changes
Total energy
Water phases present?
Heating curves
Why are b and d flat?
Boiling vs. melting
Which takes more energy?(same mass)
Consider liquid gasEvaporation removes energy
Evaporative Cooling
Evaporation and volatility
• Evaporation– molecules at the surface gain enough energy
to overcome attractive intermolecular forces (IMF)
• Volatility– measure of evaporation rate– depends on temperature and IMF
Volatility
Kinetic Energy
# o
f P
art
icle
s
Boltzmann Distribution
temp
volatility
IMF
volatility
Boiling – Fixed temperature
Why do liquids boil?• Boiling Point
–T at which liquid vapor pressure = atmospheric pressure• depends on Patm & IMF
–Normal boiling point - b.p. at 1 atm
IMF b.p.Patm b.p.
Temperature/pressure phase diagram for water
Transition to Supercritical CO2
Interpret phase diagram for water
Draw a phase diagram for NH3
(used as a refrigerant in RV’s and solar cooling systems)
Ammonia phase diagram
Phase Changes Need to know…
• Know why liquids and solids exist at all– Failure of KMT postulate
• Know phase names and changes – molecular views of phases and changes– distinguish S vs. L on molecular level
• Explain heating curve origins and parts– Why no change in T during phase change?
• Explain differences and similarities between evaporation, volatility and boiling
• Explain evaporative cooling on a molecular level
• Interpret temperature-pressure phase diagrams
