Liquids & Solids
Chapter 10
Heat of Fusion/Vaporization
H2O(s) ----> H2O(l) Hfo = 6.02 kj/mol
H2O(l) ----> H2O(g)
Hvo = 40.7 kj/mol
From the Ho values above, which two states are
most similar?
How do the attractive forces between the molecules
compare in these two states to the third state?
Three States of Matter
Types of Bonding
Intramolecular
Intermolecular
• within the molecule
•between molecules
•covalent bonding
•dipole-dipole forces
•ionic bonding
•hydrogen bonding
•London Dispersion
Forces
When ice changes to liquid and then to vapor, the
intramolecular forces (covalent bonds) stay intact, only
the weaker hydrogen bonds between molecules weaken
and break.
Intermolecular Forces
Forces between (rather than within) molecules.
-
dipole-dipole attraction: molecules with
dipoles orient themselves so that “+” and
“” ends of the dipoles are close to each
other. (1 % as strong as covalent or ionic.)
-
hydrogen bonds: dipole-dipole attraction in
which hydrogen is bound to a highly
electronegative atom. (F, O, N)
10_208
–
–
+
+
(a)
–
+
+
–
–
+
–
+
+
–
–
+
–
–
+
+
Attraction
Repulsion
(b)
Electrostatic interaction of two polar molecules.
The polar water molecule and hydrogen bonds
among water molecules.
10_210
100
H2 O
Group 6A
Boiling point ( °C)
HF
0
H 2Te
SbH3
Group 7A
H 2Se
NH 3
H 2S
– 100
AsH 3
HCl
Group 5A
SnH4
HBr
GeH4
PH3
Group 4A
HI
SiH 4
CH 4
– 200
2
3
4
5
Period
The boiling points of the covalent hydrides of the
elements in Groups 4A, 5A, 6A, & 7A.
10_211
+
+
Atom A
Atom B
H
–
+
+
Atom A
Atom B
–
H
H
Molecule A
H
Molecule B
Instantaneous dipole on molecule A
induces a dipole on molecule B
+
–
+
H
+
+
Atom A
Atom B
(a)
Molecule B
+
H
Instantaneous dipole on atom A
induces a dipole on atom B
+
H
No polarization
+
–
H
Molecule A
No polarization
–
H
H
Molecule A
–
+
H
H
Molecule B
(b)
Instantaneous and induced dipole moments
between nonpolar molecules -- London
Dispersion Forces.
London Dispersion Forces
-
relatively weak forces that exist among
noble gas atoms and nonpolar molecules.
(Ar, C8H18)
-
caused by instantaneous dipole, in which
electron distribution becomes asymmetrical.
-
the ease with which electron “cloud” of an
atom can be distorted is called
polarizability.
Some Properties of a Liquid
Surface Tension: The resistance to an
increase in its surface area (polar molecules).
A sphere has the maximum volume for the
minimum surface area.
Some Properties of a Liquid
Capillary Action: Spontaneous rising of a liquid
in a narrow tube.
Viscosity: Resistance to flow (molecules with
large intermolecular forces).
Some Properties of a Liquid
Cohesive forces exist between molecules of a
liquid. Adhesive forces exist between the
liquid and its container.
Types of Solids
Crystalline Solids: highly regular
arrangement of their components [table salt
(NaCl), pyrite (FeS2)].
Amorphous solids: considerable disorder in
their structures (glass).
Representation of Components
in a Crystalline Solid
Lattice: A 3-dimensional system of
points designating the centers of
components (atoms, ions, or molecules)
that make up the substance.
Representation of Components
in a Crystalline Solid
Unit Cell: The smallest repeating unit of
the lattice.
- simple cubic -- 1 atom/cell
- body-centered cubic -- 2 atoms/cell
- face-centered cubic -- 4 atoms/cell
10_213
Unit cell
Lattice
Example
(a)
Polonium
metal
Simple cubic
(b)
Uranium
metal
Body-centered
cubic
(c)
Gold
metal
Face-centered
cubic
Three cubic unit cells and the corresponding
lattices.
Simple Cubic Cell
•
1 atom per cell
•
side length (do) = 2 r
do = 2 r
Body-Centered Cell
•
2 atoms per cell
•
Body diagonal = do 3 = 4r
•
do2 -- diagonal through the base of
cube.
4r
do
Face-Centered Cell
•
4 atoms per cell
•
Face diagonal = do 2 = 4r
•
do2 -- diagonal through the face of
cube.
4r
do
10_221
1
atom
2
(a)
(b)
(c)
Face-centered cubic unit cell.
1
atom
8
Bragg Equation
Used for analysis of crystal structures and to
calculate the distance between planes in
crystals.
n = 2d sin 
d = distance between atoms
n = an integer
 = wavelength of the x-rays
10_214
d1
d1
d2
Waves in
phase before
striking atoms
Waves still
in phase
Waves reinforce
each other, since
(d2 - d1) is an
integral number of
X- ray wavelengths.
d2
Waves in
phase before
striking atoms
No resultant
wave
Waves cancel,
because in this case
(d2 - d1) is one half
X- ray wavelengths.
Reinforcement or cancellation of X-rays.
10_215
Incident rays
Reflected rays
w


 
d
x
z
y
Reflection of X-rays of wavelength  from a pair
of atoms in two different layers of a crystal.
Types of Crystalline Solids
Atomic Solid: contains atoms at the lattice
points (diamond).
Ionic Solid: contains ions at the points of the
lattice that describe the structure of the solid
(NaCl).
Molecular Solid: discrete covalently bonded
molecules at each of its lattice points (sucrose,
ice).
10_216
= Cl
= Na
Sodium chloride
=C
Diamond
(a)
(b)
= H2O
Ice
(c)
Three crystalline solids -- a) atomic solid, b) ionic
solid, and c) molecular solid.
Packing in Metals
Model: Packing uniform, hard spheres to
best use available space. This is called
closest packing. Each atom has 12 nearest
neighbors.
- hexagonal closest packed (“aba”)
- cubic closest packed (“abc”)
10_217
View from above
View from side
(a)
(b)
(c)
Closest packing arrangement of uniform spheres -aba. This forms hexagonal closest packed -- hcp.
10_218
(a)
(b)
(a))
Top view
Atom in third layer
lies over atom in
first layer.
Atoms arranged in aba pattern forming hexagonal
closest packed (hcp) structure -- 2 atoms/cell.
10_220
b
9
8
7
a
5
4
6
3
1
b
2
10
12
11
hcp
Hexagonal closest packed structure -- central
atom has 12 nearest neighbors.
Face-centered cubic is cubic closest packed
(ccp). The spheres are packed in an abc
arrangement.
Bonding Models for Metals
Electron Sea Model: A regular array of
metals in a “sea” of electrons.
Band (Molecular Orbital) Model: Electrons
assumed to travel around metal crystal in
MOs formed from valence atomic orbitals of
metal atoms.
Conduction Bands: closely spaced empty
molecular orbitals allow conductivity of heat
and electricity.
10_225
Empty MOs
3p
Energy
3s
Filled MOs
2p
2s
1s
12 +
12+
12 +
12+
12 +
Magnesium
atoms
Representation of the energy levels (bands) in a
magnesium crystal. 1s, 2s, & 2p orbitals are
localized, but 3s & 3p orbitals are delocalized to
make molecular orbitals.
Metal Alloys
Substances that have a mixture of elements and
metallic properties.
1. Substitutional Alloy: some metal atoms
replaced by others of similar size.
brass = Cu/Zn
Metal Alloys
(continued)
2. Interstitial Alloy: Interstices (holes) in
closest packed metal structure are
occupied by small atoms.
steel = iron + carbon
3. Both types: Alloy steels contain a mix of
substitutional (Cr, Mo) and interstitial
(Carbon) alloys.
Substitutional
Alloy
Interstitial Alloy
Network Solids
Composed of strong directional covalent
bonds that are best viewed as a “giant
molecule”.
- brittle
- do not conduct heat or electricity
- carbon, silicon-based
graphite, diamond, ceramics, glass
10_229
(a)
Diamond
Network solid structure of diamond.
Semiconductors
A substance in which some electrons can
cross the band gap.
-
Conductivity is enhanced by doping with group
3a or group 5a elements.
-
n-type semiconductor -- doped with atoms
having more valence electrons -- Phosphorus.
-
p-type semiconductor -- doped with atoms
having fewer valence electrons -- Boron.
-
See Figure 10.31 on page 477 in Zumdahl.
Molecular Solids
•
molecular units at each lattice position.
•
strong covalent bonding within molecules.
•
relatively weak forces between molecules.
•
London Dispersion Forces -- CO2, I2, P4,
& S8.
•
Hydrogen Bonding -- H2O, NH3, & HF.
Trigonal, Tetrahedral, &
Octahedral Holes
Trigonal holes -- formed by three spheres in
the same layer.
Tetrahedral holes -- formed when a sphere sits
in the dimple of three spheres in an
adjacent layer.
Octahedral holes -- formed between two sets
of spheres in adjoining layers of closest
packed structures.
10_238
Trigonal
hole
(a)
Tetrahedral
hole
(b)
Octahedral
hole
(c)
Trigonal, Tetrahedral, and Octahedral holes.
Hexagonal & Cubic Closest
Packed
1 octahedral hole for each atom or ion.
2 tetrahedral holes for each atom or ion.
Simple cubic and body-centered cubic are not
closest packed structures!
10_239
ZnS
(a)
(b)
(c)
The location (x) of a tetrahedral hole in the facecentered cubic unit cell. The S2- ions are
closest packed with the Zn2+ ions in alternating
tetrahedral holes.
10_240
(a)
(b)
The location (x) of an octahedral hole in the facecentered cubic unit cell. The Cl- ions have a ccp
arrangement with the Na+ ions in all the
octahedral holes.
Vapor Pressure
. . . is the pressure of the vapor present at
equilibrium.
. . . is determined principally by the size of
the intermolecular forces in the liquid.
. . . increases significantly with temperature.
Volatile liquids have high vapor pressures.
Vapor Pressure
Low boiling point
•
high vapor pressure.
•
weak intermolecular forces.
Low vapor pressure
•
high molar masses.
•
strong intermolecular forces.
T1
(a)
Energy needed
to overcome
intermolecular
forces in liquid
Kinetic energy
Number of molecules
with a given energy
Number of molecules
with a given energy
10_245
Energy needed
to overcome
intermolecular
forces in liquid
T2
(b)
Kinetic energy
Boltzman Distribution -- number of molecules in
a liquid with a given energy versus kinetic energy
at two different temperatures.
Natural Log of Vapor Pressure Versus
Reciprocal Kelvin Temperature
y =
ln (P
vap
m
x + b
H vap  1 
)
 C
R T
H vap
Slope =  R
If the slope is known,
then H can be calculated.
Clausius-Clayperon Equation
P
ln 
P
 H  1 1 
 
  
R  T1 T2 
1 
2

ln 






Temperatures must be expressed in Kelvin.
See Example 10.6 on page 488 in Zumdahl.
Sublimation
•Change of a solid
directly to a vapor
without passing through
the liquid state.
•Iodine
•Dry Ice
•Moth Balls
Melting Point
Molecules break loose from lattice points and
solid changes to liquid. (Temperature is constant
as melting occurs.)
vapor pressure of solid = vapor pressure of liquid
Boiling Point
Constant temperature when added energy is used
to vaporize the liquid.
vapor pressure of liquid = pressure of
surrounding atmosphere
Phase Diagram
Represents phases as a function of temperature and
pressure.
critical temperature: temperature above which the
vapor can not be liquefied.
critical pressure: pressure required to liquefy AT
the critical temperature.
critical point: critical temperature and pressure
(for water, Tc = 374°C and 218 atm).
10_247
140
Steam
120
Water and steam
Temperature (°C)
100
80
60
Water
40
20
Ice and
water
0
Ice
– 20
Time
Heating curve for water.
H = (ms t)ice + m Hf + (ms t) water + m Hv +
(mst)steam
E = KE & PE + PE
+ KE & PE + PE
+ PE & KE
10_249
Water vapor
Solid
water
Liquid
water
Solid and liquid water interact only through the
vapor state.
10_252
Pressure (atm)
Critical
point
Pc = 218
Solid
Liquid
1.00
P3 = 0.0060
Gas
Triple
point
Tm
T3
Tb
Tc
0
0.0098
100
374
Temperature ( ° C)
Phase diagram for water -- Tm is the regular melting
point. The solid/liquid line has a negative slope.
10_255
Critical
point
Pc =
Pressure (atm)
72.8
Liquid
Solid
P3 =
5.1
Gas
Triple
point
1.00
Tm
– 78
T3
– 56.6
Tc
31
Temperature (°C)
Phase diagram for carbon dioxide -- the solid/
liquid line has a positive slope.
10_256
oclin
ic
Rhombic
Mon
Pressure (mm Hg)
Liquid
(119°C, 0.0027 mm Hg)
(96°C, 0.0043 mmHg)
Vapor
Temperature (°C)
Phase diagram for sulfur -- note the two different
solid forms of rhombic and monoclinic sulfur.
10_257
1011
Diamond
Pressure (Pa)
Liquid
109
Graphite
107
Vapor
0
2000
4000
6000
Temperature (K)
Phase diagram for carbon -- note the two solid
forms of diamond and graphite.