Chapter Eleven
1
States of Matter and
Intermolecular Forces
Chapter Nine
2
Chapter Preview
(page 433)
• ___________ ______ (bonds) govern molecular
properties such as molecular geometries and
dipole moments.
• ______________ _____ determine the
macroscopic physical properties of liquids and
solids.
• This chapter:
– describes changes from one state of matter to another.
– explores the types of intermolecular forces that
underlie these and other physical properties of
substances.
Chapter Nine
3
Molecular Forces Compared
Figure 11.1 (page 434)
Chapter Nine
4
States of Matter Compared
Intermolecular
forces are of little
significance; why?
Intermolecular
forces must be
considered.
Intermolecular
forces are very
important.
Figure 11.2 (page 434)
Chapter Nine
5
Phase Changes
Vaporization and Condensation (page 435)
• _____________ is the conversion of a liquid to a gas, l  g, this is a
process. (Later we will have _____)
• The ________ __ ___________ (DHvapn) is the quantity of heat that
must be absorbed to vaporize a given amount of liquid at a constant
temperature. The heat associated with the process of vaporization.
• _______________ is the reverse of vaporization. So many things in
chemistry occur in opposites.
• The ________ __ __________ (DHcondn) accompanies this change of a
gas to a liquid, ______.
• Enthalpy is a function of state: therefore, if a liquid is vaporized and
the vapor condensed at constant temperature, the total DH must be
zero:
DHvapn + DHcondn = 0
DHcondn = – DHvapn  Note the sign change
Chapter Nine
6
page 435
Chapter Nine
7
Problem 17:
How much heat, in kilojoules, is required to
vaporize 3.530 kg of octane, C8H18?
Answer:
Chapter Nine
8
Vapor Pressure
• The ______ _________ of a liquid is the partial
pressure exerted by the vapor when it is in
dynamic equilibrium with the liquid at a constant
temperature.
_________
Liquid
Vapor
__________
I remember hearing about this in Chapter 5
Chapter Nine
9
Liquid–Vapor Equilibrium
More vapor forms; rate
of condensation of that
vapor increases …
… until __________
is attained.
Figure 11.3 (page 437)
Chapter Nine
10
Boiling Point and Critical Point
• _______ ____: the temperature at which the vapor
pressure of the liquid equals the external pressure.
• _______ _______ _____: boiling point at 1 atm.
• Critical temperature (Tc): the highest temperature at which a liquid
can exist.
• The critical pressure, Pc, is the vapor pressure at the critical
temperature.
• The condition corresponding to a temperature of Tc and a pressure of
Pc is called the critical point.
Chapter Nine
11
Phase Changes Involving Solids (page 442)
• _______ (fusion): transition of solid  liquid.
• _______ ______: temperature at which melting occurs.
– Same as freezing point!
• _______________, DHfusion, is the quantity of heat required
to melt a set amount (one gram, one mole) of solid.
• ______________: transition of solid  vapor.
– Example: Ice cubes slowly “disappear” in the freezer.
• __________________, DHsubln, is the sum of the enthalpies
of fusion and vaporization.
• ______ ____: all three phases—solid, liquid, vapor—are in
equilibrium.
Chapter Nine
12
** This is what happens to a snowball in Hades **
We are at the _______ ____.
The temperature of the solid
remains ________ until the
melting is complete.
We are heating a liquid: q =
We have a phase change, sl
q=
We are heating a solid: q =
Below
freezing
The temperature of the solid
_________ as it is heated …
Supercooled snowball
Figure 11.8 (page 444)
Chapter Nine
13
** Phase Diagrams
A—D, solid-liquid equilibrium.
_____ phases exist on this line.
A ______ _________ is a
graphical representation
of the conditions of
___________ __ _______
under which a substance
exists as a solid, liquid, a
gas, or some combination
of these in equilibrium.
A—B, solid-vapor equilibrium.
_____ phases exist on this line.
(page 445)
**
A—C, liquid-vapor equilibrium.
_____ phases exist on this line.
Triple point. All three phases, s, l, g, are
in equilibrium at this point.
Chapter Nine
14
** Phase Diagram for H2O **
Figure 11.13 (page 447)
Chapter Nine
15
** Intermolecular Forces (page 450) **
• … are forces _______ molecules.
• They _________ melting points, freezing points, and other
_________ __________.
• Types of intermolecular forces include:
• ____________ (aka London) forces
Dispersion forces arise because the electron cloud
is not perfectly uniform.
Tiny, momentary dipole moments can exist even
in nonpolar molecules.
• ______________ forces.
In molecules with permanent dipoles
• _________________ (a special type of dipole-dipole
force)
Chapter Nine
16
** Dispersion Forces Illustrated **
At a given instant, electron density, even in a nonpolar
molecule like this one, is ___ __________ ________.
… the other end of the molecule is slightly (+).
The region of (_____________)
higher electron density attains
a small (–) charge …
When another nonpolar
molecule __________ …
Chapter Nine
17
… this molecule
_________ a tiny
dipole moment …
… in this
molecule.
Opposite charges ________.
This is the ____________ _____ of
attraction known as the
____________ (London) force.
Chapter Nine
18
Strength of Dispersion Forces
• Dispersion force strength depends on
______________: the ease with which the electron
cloud is distorted by an external electrical field.
• The ________ the polarizability of molecules, the
_________ the dispersion forces between them.
• Polarizability in turn depends on molecular size
and shape.
• Heavier molecule => more electrons => a morepolarizable molecule.
Chapter Nine
19
** Dipole–Dipole Forces **
• A ______ _______ has a positively charged “end”
(δ+) and a negatively charged “end” (δ–).
• When molecules come close to one another,
repulsions occur between like-charged regions of
dipoles. Opposite charges tend to attract one
another.
• The more polar a molecule, the more pronounced
is the effect of dipole–dipole forces on physical
properties.
Chapter Nine
20
** Dipole–Dipole Interactions (page 452) **
__________
attract!
Chapter Nine
21
** Hydrogen Bonds
(page 454)
**
• A _________ ______ is an intermolecular force in
which:
– a _________ ____ that is covalently bonded to a (small,
electronegative) nonmetal atom in one molecule …
– is simultaneously attracted to a (small, electronegative)
nonmetal atom of a neighboring molecule.
Y ––– H - - - Z ~~~~
When Y and Z are small
and highly electronegative
(__________) …
… this force is called a
________ ____; a special,
______ type of dipole–
dipole force.
Chapter Nine
22
** Hydrogen Bonds in Water **
Figure 11.20 (page 455)
Chapter Nine
23
Hydrogen Bonding in Acetic Acid
Hydrogen bonding
occurs __________
molecules.
Chapter Nine
24
• A strong intermolecular force—the ________ _____ forms
when a H atom covalently bonded to an O, a N, or a F
atom of one molecule is simultaneously attracted to an O, a
N, or a F atom of another molecule.
• _________ ________ accounts for some of the unusual
properties of water (for example, an unusually high boiling point and
the fact that the density of liquid water is greater than the density of ice).
• ________ _______ also governs aspects of the behavior of
biological molecules such as proteins and the nucleic acids.
• _________ _____ also accounts for the fact that …..
Chapter Nine
25
**Problem 55:**
Arrange the following substances in the expected order of
increasing boiling point: H2O, NH3, CH4, CH3CH3.
Give the reason for your ranking.
Answer:
CH4 and CH3CH3 are nonpolar. Only weak dispersion forces
NH3 has a higher non-boiling point than CH3CH3 despite
ethane’s higher molecular mass, because of hydrogen
bonding.
In H2O, hydrogen bonding is stronger still.
Chapter Nine
26
Liquids and Intermolecular Forces
(page 459)
• Much behavior and many properties of liquids can be
attributed to intermolecular forces.
• ________ ________ (g) is the amount of work required to
extend a liquid surface and is usually expressed in J/m2.
• ________ _____ are intermolecular forces between unlike
molecules.
• _________ ______ are intermolecular forces between like
molecules.
• A _________ is the interface between a liquid and the air
above it.
• _________ is a measure of a liquid’s __________ to flow.
Chapter Nine
27
Surface Tension
Molecules within the bulk of a liquid are
attracted to more neighboring molecules
than are _______ molecules.
Figure 11.26 (page 459)
Chapter Nine
28
Meniscus Formation
What conclusion
can we draw about
the ________ ____
in mercury?
Water wets the
glass (__________
________) and its
attraction for glass
forms a concaveup surface.
Chapter Nine
29
Comparing Viscosity
The flow of the oil is started at the same
time. Which oil flows more readily?
Which oil has stronger intermolecular
forces between its molecules?
Oil is mostly hydrocarbons; what kind of
forces are these?
Figure 11.31 (page 461)
Highly viscous
Less viscous
Chapter Nine
30
Types of Solids
• Amorphous solids have no significant long-range
order.
• Crystalline solids have atoms/ions/molecules
arranged in a regular pattern. Types of crystalline
solids include:
– Molecular solids, containing molecules held to
one another by dispersion/dipole–dipole/
hydrogen bonding forces.
– ________ (covalent) solids.
– _____ solids.
– _______ solids (metals).
Chapter Nine
31
** Network Covalent Solids **(page 462)
• Network solids have a network of covalent bonds that
extend throughout the solid, holding it firmly together.
• The allotropes of carbon provide good examples.
• __________ – Two or more forms of an element that differ
in their basic molecular structure.
• Carbon Allotropes
– _______ has each carbon bonded to four other carbons
in a tetrahedral arrangement using sp3 hybridization.
– _______ has each carbon bonded to three other carbons
in the same plane using sp2 hybridization.
– __________ are roughly spherical collections of carbon
atoms in the shape of a soccer ball.
– A _________ can be thought of as a plane of graphite
rolled into a tube.
Chapter Nine
32
_________: Allotrope of carbon
Three-dimensional network of
____ hybridized carbon atoms.
Extremely strong, rigid.
_________: Allotrope of carbon
Three-dimensional network of
____ hybridized carbon atoms.
Forces _______ layers are
relatively weak.
Chapter Nine
33
Ionic Bonds as
“Intermolecular” Forces
(page 464)
• There are no molecules in an ionic solid, and therefore
there can’t be any intermolecular forces.
• The attractions are electrostatic interionic attractions.
• _______ ____ (Chapter 9) is a measure of the strength
of interionic attraction.
• The attractive force between a pair of oppositely
charged ions _________:
– as the ________ on the ions ________.
– as the ionic radii _________.
• Lattice energies increase accordingly.
Chapter Nine
34
Interionic (between ions) Forces of Attraction
Melting point of NaCl
is about 801 oC.
Mg2+ and O2– have much stronger forces of
attraction for one another than do Na+ and Cl–
. Melting point of MgO is about 2800 oC.
Figure 11.36 (page 465)
Chapter Nine
35
Crystal Lattices
(page 466)
• To describe crystals, three-dimensional views
must be used.
• The repeating unit of the lattice is called the _____
_____.
• There are a number of different types of unit cell;
hexagonal, rhombic, cubic, etc.
• The three types of _____ unit cells are: simple
cubic, body-centered cubic (bcc), face-centered
cubic (fcc).
Chapter Nine
36
Cubic Unit Cells
simple
cubic
body-centered
cubic
Figure 11.39 (page 467)
face-centered
cubic
The unit cell is
a ____ in each
case.
Whole atoms
shown for
clarity.
Chapter Nine
37
Unit Cells – Coordination Number
The ____________ ______ is the number of nearest
neighbor particles to a single particle in the crystal
In a ______ ____
structure, the
coordination
number is __
(__ nearest neighbors)
Chapter Nine
38
1.
___________ - 1 Atom at each of the corners of a cube. These atoms are shared
equally with adjacent unit cells. The coordination number is 6.
(8 corners) (1/8 atom at corner) = 1 atom/unit cell
2.
_________________ - 1 atom at each of the corners of a cube. These atoms are
shared equally with adjacent unit cells, plus 1 atom in the center. The coordination
number is 8.
(8 corners) (1/8 atom at corner) + 1 atom in center = 2 atoms/unit cell
3.
_________________ - 1 atom at each of the corners of a cube. These atoms are
shared equally with adjacent unit cells plus 1 atom at each of the 6 faces of the
cube. The coordination number is 12.
(8 corners) (1/8 atom at corner) + (6 faces) (1/2 atom/face) = 4 atoms/unit cell
Chapter Nine
39
Close-Packed Structures
A _____ _______
structure in two
dimensions.
Figure 11.42 (page 468)
Chapter Nine
40
Sum and Substance
• A ________, when repeated in three dimensions, generates
the entire crystal lattice.
• Unit cell properties and dimensions, often measured by Xray crystallography, can be used to find atomic radii and
the densities of crystalline substances.
• The crystal structures of metals can be described as the
packing of spheres.
• The two types of close-packing of spheres, ___________
_______ ______ (hcp) and _______________ (ccp), both
reduce to the smallest possible fraction the volume
occupied by holes or voids.
Chapter Nine