AP Notes Chapter 12 & 13
Intermolecular Forces, Liquids and Solids
1. Ion - Ion
Dissociation Energy
Opposite of
Lattice Energy
MX (s) 
+
M (g)
(g)
+
X
1. Ion - Ion
2. Ion - Permanent
Dipole
Hydrated Ions
A
particle that is only
weakly polar but is much
larger than ion alone
 The number of waters of
hydration depends on
size of ion and strength
of charge to be stabilized
(typically less than 5)
1. Ion - Ion
2. Ion - Permanent
Dipole
3. Dipole - Dipole
Occurs between
molecules with
permanent dipoles
(SO2 , CHCl3 , etc)
Hydrogen-Bonding
 Relatively
strong
attraction between a
hydrogen atom in one
molecule and a highly
electronegative atom
(F, O, N) in a different
molecule
Hydrogen-Bonding
Strong enough to
produce a phase
change in a compound
that should be more
random at that
temperature
(about 1.5 kJ)
Dimer of
Acetic Acid
Hydrogen-Bonding
How and why of
bonding is not clear most likely due to
strong attraction
between e cloud of the
highly EN atom and the
nucleus of the H atom
QUESTION
Is the hydrogen bond a
“true” chemical bond
or is it just a very
strong electrostatic
attraction?
1.
2.
3.
4.
Ion - Ion
Ion - Dipole
Dipole – Dipole
Dipole-Induced Dipole
1.
2.
3.
4.
5.
Ion - Ion
Ion - Dipole
Dipole – Dipole
Dipole-Induced Dipole
Dispersion Forces
Dispersion Forces
Process of distorting an
electron cloud by
electrostatic forces of
attraction and
repulsion.
Weakest of the
intermolecular forces.
Non-polar
molecules
Momentary
attractions
&
repulsions
Temporary
dipoles
established
Dispersion forces also
called
van der Waal’s forces
LIQUIDS & SOLIDS
Cohesive Forces
various
intermolecular
forces holding a
liquid together
Vaporization
Process in which a
substance in the liquid state
becomes a gas.
 Vaporization requires
energy since it involves
separation of particles that
are attracted to one
another.

Standard Molar
Enthalpy of
Vaporization, Hºvap



Energy required to convert one mole
of liquid to one mole of the
corresponding gas at the BP.
Always endothermic, Hvap is positive.
Liquids having greater attractive
forces have higher Hvap
Condensation
1
2
KE  mv
2
Opposite of Evaporation
Condensation -- Exothermic
Viscosity
a measure of the
resistance to flow
of a liquid
Ethylene Glycol & EtOH
Surface Tension
the force that
causes the
surface of a
liquid to contract
Paper Clip
Adhesive Forces
the forces of
attraction
between a
liquid and a
surface
Capillary Action
Meniscus
SOLIDS
Amorphous Solids
Arrangement of particles
lacks an ordered
internal structure. As
temp is lowered,
molecules move slower
and stop in somewhat
random positions.
Crystalline Solids
Atoms or ions are held in
simple, regular geometric
patterns
Ionic
Molecular
Atomic
Atomic Solids
Noble Gases
Network
Metallic
X-ray Crystallography
How do you
determine the
spacing and position
of atoms in an
organized solid like
a crystal?
X-ray Crystallography
Bragg discovered that
nuclei of atoms or ions
in a crystal will defract
x-rays and form a
pattern on photofilm
that can be analyzed
using simple trig &
geometry
X-ray Crystallography
Use the fact that x-rays are
part of the electromagnetic
spectrum
Nuclei in crystalline solids
are in layers that can act as
a diffraction grating to the
x-ray wavelength
Crystalline Solids
Diffract X-rays
Let D = “extra”
distance that i’ must
travel so that r’ is inphase with r
D = xy + yz
or D = 2xy
Using trigonometry:
xy
sin  
d
 xy  d sin 
 D  2 d sin
But for
constructive interference
But for
constructive interference
D = nl
nl = 2d sin 
BRAGG EQUATION
1. X-rays from a copper
x-ray tube (l = 154 pm)
were diffracted at an
angle of 14.220 by a
crystal of Si. What is
the interplanar spacing
in silicon?
Solids
Types of Solids
1. Atomic (Metals)
2. Molecular (Ice)
3. Ionic (NaCl)
Structures of Metals
The unit cell is the
smallest
representation of the
building block of the
regular lattice
Unit Cell
Only 23 different unit
cells have been defined
Called Brave’ Lattices
Patterns are determined
by crystallography
Coordination Number
CN is related to net
atoms found
within the unit cell
CN is the number of
atoms closest to any
given atom in a crystal
There are three Cubic Unit Cell Types
(pc) primitive cubic or simple cubic
(8 corners of cube) x (1/8 each corner in cell) = 1 net atom in cell
CN = 6
(bcc) body centered cubic
(1 atom in cube) +
[(8 corners of cube) x (1/8 each corner in cell)] = 2 net atoms in cell
CN = 8
(fcc) face centered cubic
[(6 faces of cube) x (1/2 of atom in cell)] +
[(8 corners of cube) x (1/8 each corner in cell)] = 4 net atoms in cell
or
CN = 12
(1 atom in cube) +
[(12 edges of cube) x (1/4 each edge in cell)] = 4 net atoms in cell
CN = 12
1 Atom per Cell
l
CN = 6
l = 2r
2 Atoms per Cell
l
CN = 8
 
2

  2

2
4r
 
3
 4r 
2
l
4 Atoms per Cell
CN = 12
 
2
    4r 
2
  2r 2
2
Summary
Atoms
Unit
Per
Cell
Cell C.N.
Cubic
1
6
BCC
2
8
Length
Of Side
2r
4r
3
FCC
4
12
2r 2
Primitive cubic
Face-centered cubic
Structures of Metals
Closest Packing
Structures of Metals
Closest Packing
1. Hexagonal
2. Cubic
A-B
A-B-C
(Primitive cubic)
2. Al crystallizes as a
face centered cube.
The atomic radius of
Al is 143 pm. What is
the density of Al in
3
g/cm ?
3. What is the
percent of empty
space in a body
centered unit cell?
VAPOR
PRESSURE
Evaporation
and equilibrium
Vapor Pressure
pressure in space
above a liquid in a
CLOSED container
PROPERTIES
1. closed container
2. temperature
dependent
3. subject to all laws of
partial pressures
4. dynamic system
Vapor Pressure
temperature dependent
P
T
To plot in a linear
fashion, must
transform the
variables.
ln P
1/T (K)
y = mx + b
where : m  
DHvap
R
& R = 8.314 J/K mol
therefore:
 DHvap  1 
   b
ln P   R
T


 
define 2 points
1
ln P
2
1/T (K)
 DHvap  1 
   b
ln P1   R
T

 1 
 DHvap  1 
   b
ln P2    R  T2 
Subtract: ln P1 - ln P2
 DHvap  1  
   b
 R
T


 1 

 DHvap  1  
   b
-  R
T


 2 

Collect terms & factor:
 P1  DHvap  1 1 
  
ln  
P
R
T
T
1
 2
 2
ClausiusClapeyron
Equation
SUMMARY OF IDEAS
TO BE CONSIDERED:
1. vapor pressure temperature dependent
2. volume determines time
needed to establish
vapor pressure NOT final pressure
3. DH (condensation) =
-DH (vaporization)
4. Critical Point (T,P) above which vapor
cannot be liquefied
- regardless of pressure
5. Boiling: temperature
where vapor pressure
of liquid is the same as
atmospheric pressure
4. The temperature
inside a pressure
0
cooker is 115 C. What
is the vapor pressure
of water inside the
pressure cooker?
PHASE
DIAGRAMS
PHASE DIAGRAM
A representation of the
phases of a substance in
a closed system as a
function of temperature
and pressure
Normal Boiling Point
Temperature at which
the vapor pressure of
the liquid is exactly 1
atmosphere
Normal Melting Point
Temperature at which
the solid and liquid
states have the same
vapor pressure when
the total P = 1 atm
Triple Point
The point on a phase
diagram at which all
three states of a
substance are present
Critical Temperature
Temperature above
which vapor cannot be
liquified no matter what
pressure is applied
Critical Pressure
Minimum pressure
required to produce
liquefaction of a
substance at the
critical temperature
Critical Point
Ordered pair of
Critical Temperature
& Critical Pressure
CO2
H2O
sulfur