Intermolecular Forces of Attraction
1. Compare using the KMT solids, liquids and gases on the molecular level.
2.The physical properties of a substance depend upon a given substance’s intermolecular
forces.
A.Vapor Pressure of a substance that exists as a vapor at that temperature.
i. the amount
i. Inverse relationship
Vapor Pressure
IMF
B. Boiling Point VOLATILE-easy to boil or evaporate
i. vapor pressure of a substance equals atmospheric pressure
ii. the normal boiling point is when the vapor pressure equals 760 mm Hg
or standard atmospheric pressure
pentane <butanal <butanol
iii. direct relationship
boiling point
IMF
36°C < 76°C < 118°C
C. Heat of Vaporization
MM
72,
72
74 g
i. the amount of energy needed to turn a specific quantity of liquid to gas.
II. direct relationship
H vap
IMF
D. Surface Tension
i. water and Hg have strong intermolecular forces that pull the molecules
together.
E.Viscosity
i. resistance to flow
ii. Honey, molasses, ketchup
3. Types of intermolecular forces
How it Works
Factors to
Type of molecules
Example
Type of Force
consider
Attraction as a result of
Polarizability
nonpolar
Ar, F2
Dispersion Forces
Temporary or instantaneous
(London Forces)
dipoles
dipole moment Polar molecules
SO2
Dipole-dipole forces Attraction of permanent
partial charges the + and  –
ends of two polar molecules
Attractions between a
Polar molecules with H2O, HF
Hydrogen Bonding
hydrogen that is attached to a
hydrogen attached to CH3OH
–N, -O or –F to another –N, -N, -O, or -F
O or -F
A. The polarizability of an atom or molecule is influenced by its size and molar
mass.
i.Polarizability-the ability of an electron cloud to shift or distort position
around the nucleus.
ii. the larger the surface area, the larger the attractive forces between two
molecules and the stronger the intermolecular forces.
B. The general trend for relative strengths of intermolecular forces is
Hydrogen bonding > dipole-dipole forces > dispersion forces
i. remember that this is just a trend so exceptions can occur.
ii. all molecules have dispersion forces, but they are only important when
there are no other IMF possible.
3. X-ray Diffraction by Crystals
A. Bragg Equation n = 2 d sin O
i. d = distance between layers or points in the crystal
4. Forces in Solids
Type of Solid
Example
Exist as
Type of
Attraction
NaCl
CaO
crystal
Attraction
between ions
solidification
condensation
Properties
Strength of
Attractive Forces
kJ/mole
400 to 4000
Hard, high mp
Solid does not
conduct
Diamond Network of 3-D network of high mp poor
150 to 500
Network
atoms
covalent bonds conductor
SiO2
(Covalent)
Individual Attraction
Low mp < 100°C
0.05 to 40
H2O,
Molecular
molecules
between
poor
conductor
sugar
molecules
Cu,
Fe
Atoms
Delocalized
Low to high mp
75 to 1000
Metallic
held
metallic
solid good
together by bonding
conductor of heat or
a “sea”
electricity
of valence
electrons
A. amorphous solids-without shape or form, solids that lack a three dimensional arrangement
of atoms. No sharp melting point or boiling point.
i.Examples: glass, rubber, gum, play dough
5. Phase Changes
melting
vaporization
solid
liquid
gas
Ionic
6. To be able to draw and interpret Phase Diagrams
A. -summarizes the conditions at which a pure substance exists as a solid, liquid or
gas.
B. Critical Point
i. Critical Temperature, Tc -a temperature above which the gas phase cannot be made
into a liquid no matter how large the pressure applied.
ii. Critical Pressure, Pc -is the maximum pressure that must be applied to turn a
substance into a liquid at the critical temperature.
C. Triple Point-all three phases are in equilibrium with each other.
D. Water
E. Carbon Dioxide Sublimation occurs at normal pressures
P
R
E
S
S
U
R
E
critical point
(at constant pressure, follow this type of line)
Liquid
Solid
triple point
Temperature
Gas
(at constant temperature)