Intermolecular Forces
and
Liquids and Solids
Chapter 11
11장 분자간 힘과 액체와 고체
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11.1 액체와 고체의 분자운동론
11.2 분자간 힘
11.3 액체의 특징
11.4 결정구조
11.5 고체의 결합
11.6 상변화
11.7 상평형 그림
기체, 액체, 고체
• 기체와 액체의 차이점은
무엇인가?
• 액체와 고체의 차이는?
• 액체와 고체의 비슷한 점은?
• 기체와 액체의 비슷한 점은?
기체, 액체, 고체
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어떻게 액체 분자들이 모여 있게 할까?
어떻게 고체 분자들은 질서가 있을까?
온도는 이들 사이에 어떤 역할을 하나?
어떻게 액체와 기체를 구분하나?
항상 액체와 기체는 구별할 수 있을까?
Phase (상)
A phase is a homogeneous part of the system in
contact with other parts of the system but
separated from them by a well-defined boundary.
Intermolecular Forces
Intermolecular forces are attractive forces between molecules.
Intramolecular forces hold atoms together in a molecule.
Intermolecular vs Intramolecular
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41 kJ to vaporize 1 mole of water (inter)
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930 kJ to break all O-H bonds in 1 mole of water (intra)
“Measure” of intermolecular force
Generally,
intermolecular
forces are much
weaker than
intramolecular
forces.
boiling point
melting point
DHvap
DHfus
DHsub
Intramolecular Forces
Intramolecular forces hold atoms together in a molecule.
• Ionic bonding
•
Covalent bonding
•
Metallic bonding
Bond type
Ionic bonds
Hydrogen bonds
Dipole-dipole
London Forces
Relative strength
1000
100
10
1
Note: this comparison is only approximate- the actual relative strengths will vary depending on the molecules involved.
Intermolecular Forces
Intermolecular forces exert forces beyond a molecule.
van der Waals forces
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dipole-dipole interaction (HCl – HCl)
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ion-dipole interaction(Na+ – HCl)
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ion-induced dipole(Na+ – Cl2)
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dipole-induced dipole(HCl – Cl2)
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induced dipole-induced dipole interaction(Br2 – Br2)
Phase Transition(상변화)
Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
Intermolecular Forces
Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
Ion-Dipole Interaction
Intermolecular Forces
Dispersion Forces (London dispersion force)
Attractive forces that arise as a result of temporary
dipoles induced in atoms or molecules
ion-induced dipole interaction
dipole-induced dipole interaction
Induced Dipoles Interacting With Each Other
Intermolecular Forces
Dispersion Forces Continued
Polarizability is the ease with which the electron distribution
in the atom or molecule can be distorted.
Polarizability increases with:
•
greater number of electrons
•
more diffuse electron cloud
Dispersion
forces usually
increase with
molar mass.
Mass
R(pm)
16
109
88
135
154
177
332
194
266
214
Q. What type(s) of intermolecular forces exist
between each of the following molecules?
HBr
HBr is a polar molecule: dipole-dipole forces. There are
also dispersion forces between HBr molecules.
CH4
CH4 is nonpolar: dispersion forces.
S
SO2
SO2 is a polar molecule: dipole-dipole forces. There are
also dispersion forces between SO2 molecules.
Intermolecular Forces
Hydrogen Bond
The hydrogen bond is a special dipole-dipole interaction
between they hydrogen atom in a polar N-H, O-H, or F-H bond
and an electronegative O, N, or F atom.
A
H…B
or
A
A & B are N, O, or F
H…A
Hydrogen Bond
Q. Why is the hydrogen bond considered a “special”
dipole-dipole interaction?
Decreasing molar mass
Decreasing boiling point
Properties of Liquids
Surface tension is the amount of energy required to stretch
or increase the surface of a liquid by a unit area.
Strong
intermolecular
forces
High
surface
tension
Properties of Liquids
Cohesion is the intermolecular attraction between like molecules
Adhesion is an attraction between unlike molecules
Adhesion
Cohesion
Properties of Liquids
Viscosity is a measure of a fluid’s resistance to flow.
Strong
intermolecular
forces
High
viscosity
Water is a Unique Substance
Maximum Density
40C
Density of Water
Ice is less dense than water
요약-액체 분자간 상호작용
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쌍극자-쌍극자(극성분자)
이온-쌍극자
분산력(유도 쌍극자) 비극성 분자
수소결합
표면장력, 점성도, 증기압, 끓는점,
녹는점
A crystalline solid possesses rigid and long-range order. In a
crystalline solid, atoms, molecules or ions occupy specific
(predictable) positions.
An amorphous solid does not possess a well-defined
arrangement and long-range molecular order.
A unit cell is the basic repeating structural unit of a crystalline
solid.
At lattice points:
lattice
point
Unit Cell
Unit cells in 3 dimensions
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Atoms
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Molecules
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Ions
6
Coordination numer
8
12
Shared by 8
unit cells
Shared by 2
unit cells
1 atom/unit cell
2 atoms/unit cell
4 atoms/unit cell
(8 x 1/8 = 1)
(8 x 1/8 + 1 = 2)
(8 x 1/8 + 6 x 1/2 = 4)
Simple Cubic
Chemtube3d:Solid State Structures
Body-Centered Cubic
Face-centered Cubic
C
B
A
Chemtube3d.com:FCC
Hexagonal close-packing(HCP)
A
B
A
Chemtube3d.com:HCP
FCC vs. HCP
Metal
Crystal
Structure
Atomic
Radius (nm)
Aluminum
Cadmium
Chromium
Cobalt
Copper
Gold
Iron (α)
Lead
Magnesium
Molybdenum
Nickel
Platinum
Silver
Tantalum
Titanium (α)
Tungsten
Zinc
FCC
HCP
BCC
HCP
FCC
FCC
BCC
FCC
HCP
BCC
FCC
FCC
FCC
BCC
HCP
BCC
HCP
0.1431
0.1490
0.1249
0.1253
0.1278
0.1442
0.1241
0.1750
0.1599
0.1363
0.1246
0.1387
0.1445
0.1430
0.1445
0.1371
0.1332
4
r
3

3

 0 . 524
3
(2r )
6
2
(
4
3
4
3
r
3

r)
3
3
8
 0 . 680
4
4
r
3

3

 0 . 740
3
( 8r )
3 2
Q. When silver crystallizes, it forms face-centered cubic
cells. The unit cell edge length is 409 pm. Calculate the
density of silver. mAg=107.9 g/mol
d=
m
V
V = a3 = (409 pm)3 = 6.83 x 10-23 cm3
4 atoms/unit cell in a face-centered cubic cell
1 mole Ag
107.9 g
-22 g
x
m = 4 Ag atoms x
=
7.17
x
10
mole Ag 6.022 x 1023 atoms
7.17 x 10-22 g
m
3
=
=
10.5
g/cm
d=
V
6.83 x 10-23 cm3
Extra distance = BC + CD = 2d sinq = nl
(Bragg Equation)
Q. X rays of wavelength 0.154 nm are diffracted from a
crystal at an angle of 14.170. Assuming that n = 1, what is
the distance (in pm) between layers in the crystal?
nl = 2d sin q
n=1
nl
q = 14.170 l = 0.154 nm = 154 pm
1 x 154 pm
=
= 77.0 pm
d=
2 x sin14.17
2sinq
Types of Crystals
Ionic Crystals
• Lattice points occupied by cations and anions
• Held together by electrostatic attraction
• Hard, brittle, high melting point
• Poor conductor of heat and electricity
Types of Crystals
Covalent Crystals
• Lattice points occupied by atoms
• Held together by covalent bonds
• Hard, high melting point
• Poor conductor of heat and electricity
carbon
atoms
diamond
graphite
Types of Crystals
Molecular Crystals
• Lattice points occupied by molecules
• Held together by intermolecular forces
• Soft, low melting point
• Poor conductor of heat and electricity
Types of Crystals
Metallic Crystals
• Lattice points occupied by metal atoms
• Held together by metallic bonds
• Soft to hard, low to high melting point
• Good conductors of heat and electricity
Cross Section of a Metallic Crystal
nucleus &
inner shell emobile “sea”
of e-
Crystal Structures of Metals
Types of Crystals
An amorphous solid does not possess a well-defined
arrangement and long-range molecular order.
A glass is an optically transparent fusion product of inorganic
materials that has cooled to a rigid state without crystallizing
Crystalline
quartz (SiO2)
Non-crystalline
quartz glass
Chemistry In Action: High-Temperature Superconductors
Chemistry In Action: Tin Pest
T < 13.2 0C
white tin
grey tin
weak
stable
Allotropic transformation
At 13.2 0C and below, pure tin transforms from
the (silvery, ductile) β-form white tin to brittle,
α-form grey tin. Eventually it decomposes into
powder, hence the name tin pest.
The decomposition will catalyze itself, which is
why the reaction seems to speed up once it
starts; the mere presence of tin pest leads to
more tin pest. Tin objects at low temperatures
will simply disintegrate.
T2 > T1
Condensation
Evaporation
Least
Order
Greatest
Order
The equilibrium vapor pressure is the vapor pressure
measured when a dynamic equilibrium exists between
condensation and evaporation
H2O (l)
Dynamic Equilibrium
Rate of
Rate of
= evaporation
condensation
H2O (g)
Before
Evaporation
At
Equilibrium
Molar heat of vaporization (DHvap) is the energy required to
vaporize 1 mole of a liquid.
Clausius-Clapeyron Equation
DHvap
ln P = +C
RT
P = (equilibrium) vapor pressure
T = temperature (K)
R = gas constant (8.314 J/K•mol)
The boiling point is the temperature at which the
(equilibrium) vapor pressure of a liquid is equal to the
external pressure.
The normal boiling point is the temperature at which a liquid
boils when the external pressure is 1 atm.
The Critical Phenomenon of C2H6
T < Tc
Tc =305.3 K (32.2 °C), 4.9 Mpa(48 atm)
T ~ Tc
T > Tc
1. Subcritical ethane, liquid and gas phase coexist
2. Critical point, opalescence
3. Supercritical ethane, fluid
Pictures from Wikipedia
The critical temperature (Tc) is the temperature above which
the gas cannot be made to liquefy, no matter how great the
applied pressure.
The critical pressure
(Pc) is the minimum
pressure that must be
applied to bring about
liquefaction at the
critical temperature.
The melting point of a solid
or the freezing point of a
liquid is the temperature at
which the solid and liquid
phases coexist in equilibrium
Freezing
H2O (l)
Melting
H2O (s)
Molar heat of fusion (DHfus) is the energy required to melt
1 mole of a solid substance.
Molar heat of sublimation
(DHsub) is the energy required
to sublime 1 mole of a solid.
DHsub = DHfus + DHvap
( Hess’s Law)
Deposition
H2O (g)
Sublimation
H2O (s)
A phase diagram summarizes the conditions at which a
substance exists as a solid, liquid, or gas.
pressure
Phase Diagram
solid
phase
supercritical
fluid
Pc
liquid
phase
1 atm
Ptp
triple point
Ttp
critical point
gaseous
phase
Tc
superheated
vapor
temperature
Phase Diagram of Carbon Dioxide
At 1 atm
CO2 (s)
CO2 (g)
5.2 atm,
-56.6 ℃
7.38 MPa,
31.1℃
Effect of Increase in Pressure on the Melting Point
of Ice and the Boiling Point of Water
Chemistry In Action: Liquid Crystals