Chapter 13
INTERMOLECULAR FORCES,
LIQUIDS, AND SOLIDS
13.0 Objectives

Use the kinetic molecular theory to compare the three states of
matter at the molecular level.

Describe and give examples of the types of intermolecular
forces: dipole-dipole interactions, hydrogen bonds, and
dispersion forces.

Explain the unusual properties of water with reference to
hydrogen bonding.

Define and explain properties of liquids; equilibrium vapor
pressure, boiling point, critical temperature, and critical
pressure.

Describe the bonding and forces inside different types of solids.

Sketch and identify various landmarks on a phase diagram;
phase boundaries, critical temperature and pressure, and triple
point.
Homework

HW#1 - 17, 19, 21, 23, 51, 53


HW#2 - 25, 27, 31, 33, 35


Liquids
HW#3 - 55, 57, 59, 71


Intermolecular Forces
“Little bit of everything”
HW#4 - 45, 47, 49

Phase Changes
13.1 STATES OF MATTER AND THE
KINETIC MOLECULAR THEORY

1. Particles in the solid, liquid and
gas states

1. Gas – “molecules far apart”

2. Liquid – “molecules closer together”

3. Solid – “molecules extremely close together”
13.1 STATES OF MATTER AND THE
KINETIC MOLECULAR THEORY

2. Internal forces: intermolecular
vs. intramolecular forces

a. Definitions


Intermolecular: forces between molecules;
molecules interact with one another
Intramolecular: forces within the molecule; hold the
atoms together (bonds)
13.1 STATES OF MATTER AND THE
KINETIC MOLECULAR THEORY

b. importance.

Combination of intermolecular and intramolecular
forces largely explains chemical properties
13.2 INTERMOLECULAR FORCES

1. Dispersion forces, London forces, van
der Waals forces, induced-dipole/induceddipole forces (all these terms are
synonymous)

a. definition and mechanism




force of attraction between induced-dipoles
Form from distortion of electron clouds when
molecules approach each other
ALL molecules have some dispersion forces acting
between them
Only force of attraction in liquids and solids of
nonpolar molecules
13.2 INTERMOLECULAR FORCES

b. Trends




As the molecular mass increases, the dispersion forces
increase; more opportunity for distortion
About 1/10 the strength of a dipole-dipole force
Occur in both nonpolar and polar molecules
Weakest of the intermolecular forces
13.2 INTERMOLECULAR FORCES

2. Dipole/dipole forces

a. definition



Permanent dipoles that try to align with + and - ends
of adjacent molecules; polar molecules
Induce some dispersion forces in addition to the
permanent + and - ends
Mid-range of the forces
13.2 INTERMOLECULAR FORCES
13.2 INTERMOLECULAR FORCES

a. trends

Higher BP and MP than their similar molar mass but
nonpolar counter parts because stronger forces from
both dipole-dipole and dispersion forces (stronger
intermolecular forces  more resistance to change
phase)
13.2 INTERMOLECULAR FORCES

3. Dipole/Induced-dipole forces

Dipoles cause nonpolar molecules to polarize
slightly, thus forming temporary dipoles

Polarization – the process of inducing a dipole

In general the greater the molar mass the more
polarizable a molecule (difficult to measure exp)
13.3 HYDROGEN BONDING

1.Definition and mechanism

Force in which a hydrogen atom covalently bonded to a
nonmetal is simultaneously attracted to a neighboring
nonmetal atom

Very large dipole in molecules
Nonmetal should be small, very electronegative
Hydrogen bonding is FON!




Usually occurs only with F, O, and N
2.Examples

H2O, NH3, HF
13.3 HYDROGEN BONDING

3. Unusual properties of water

Ice forms rigid, open structures


Molecules with higher M.M. have lower BP than
water


Increases volume upon freezing (floats)
H2O vs. CH4
Surface Tension and Capillary Action
13.3 HYDROGEN BONDING
13.4 SUMMARY OF
INTERMOLECULAR FORCES

1. Relative strengths of intermolecular
forces

Dispersion < Dipole-Dipole < Hydrogen Bonding
(Dipole/induced-dipole falls b/t disp. And d-d)

All molecules will have dispersion

Combination of these forces explain much


BP, MP, surface tension, solubility
13.4 SUMMARY OF
INTERMOLECULAR FORCES

2. Ex13.1 Arrange the following in order of increasing
melting point/boiling point:
HCl, F2, I2, HF, H2O, CH4, CH3Cl, CH3NH2, CH2O
13.5 PROPERTIES OF LIQUIDS

A. Vapor Pressure

1. Dynamic equilibrium – characteristics

“Two opposing processes occur at the same rate”
 Evaporation  Condensation

No process wins out (net of zero once equilibrium is
reached)
13.5 PROPERTIES OF LIQUIDS

2. Liquid-vapor equilibrium

Molecules of a liquid evaporate (convert from liquidgas)
in a closed vessel until equilibrium is reached between
evaporation and condensation

Hand Sanitizer Scenario:



1. Liquid has molecules with Avg. K.E. (temp)
2. Some molecules at surface have a little extra K.E., break
intermolecular attractions become gas
3. Molecules leave, thus taking some of the K.E. from liquid
(temp. falls!)
13.5 PROPERTIES OF LIQUIDS
13.5 PROPERTIES OF LIQUIDS

3. Equilibrium vapor pressure


A.k.a “Vapor Pressure”
Pressure exerted by a vapor once equilibrium is
established
13.5 PROPERTIES OF LIQUIDS

4. Ex13.2 Carbon disulfide (CS2) has a vapor pressure of 298mmHg at 20.0oC. A
sample of 6.00g of CS2 is put into a stoppered flask at that temperature. A. What is
the maximum volume of the flask if there is to be a liquid-vapor equilibrium? B. If
the flask has a volume of 3.00L, what will be the pressure of the carbon disulfide
vapor? C. If the flask has a volume of 6.00L, what will the pressure of the vapor be?
13.5 PROPERTIES OF LIQUIDS

B. Vapor Pressure and Temperature

1. See graph
Pg.13 in Reference Booklet
 Movie Clip: Heating Curve
and V.P.

13.5 PROPERTIES OF LIQUIDS

2. Clausius-Clapeyron Equation


Method for experimentally determining the Hvap
A plot of Vapor Pressure vs. 1/T (in K) is a straight line
with a slope of –Hvap/R
13.5 PROPERTIES OF LIQUIDS

3. Ex13.3 Carbon disulfide has a vapor pressure of 41.4mmHg at -22.0oC
and 100.mmHg at -5.00oC. Estimate the heat of vaporization of carbon
disulfide, and the vapor pressure of CS2 at 28.0oC.
13.5 PROPERTIES OF LIQUIDS

C. Boiling Point

1. See graph



Pg.13 in Reference Booklet
Temperature at which the vapor pressure equals
prevailing atmospheric pressure
2. Normal boiling point, Standard boiling point

Boiling point at 1 atm of pressure
13.5 PROPERTIES OF LIQUIDS

3. Vacuum pump demo

4. Pressure cooker

Operates on a similar principle…but opposite to the
vaccuum pump demo
13.5 PROPERTIES OF LIQUIDS

D. Critical Temperature and Pressure


1. Definitions
Critical point – the point where the interface
between liquid and vapor disappears



Critical temperature-temp at the critical point
Critical pressure-pressure at the critical point
Super critical fluid-state at and above critical point
that has a liquid like density and vapor like flow
13.5 PROPERTIES OF LIQUIDS

2. Ex13.4 The critical point of CO is -139oC,
35.0atm. Liquid CO has a vapor pressure of 6.00atm
at -171oC. Which of the following statements is true?




A.
B.
C.
D.
CO is a gas at -171oC and 1.00atm.
A tank of CO at 20oC can have a pressure of 35.0atm.
CO gas cooled to -145oC and 40.0atm will condense.
The normal boiling point of CO is above -171oC.
13.6 SOLID-STATE CHEMISTRY:
METALS

1. Particles and Force of Attraction


2. Properties





Cations that have delocalized e-
Conduct e- and heat
Luster
Malleable, ductile
Hardness varies from soft to hard
3. Examples

Copper, Brass, Steel
13.7 SOLID-STATE CHEMISTRY: STRUCTURES
AND FORMULAS OF IONIC SOLIDS

1. Particles and forces of attraction


2. Properties


Formed by “electrostatic interactions” between
cations and anions (lattice energy); Repeating
Structure
Hard, brittle, high MP, soluble in H2O, conduct
as liquids
3. Examples

NaCl, CaI2, LiBr
13.8 OTHER KINDS OF SOLID
MATERIALS

A. Network Covalent solids

1. Particles and forces of attraction



2. Properties


Network of covalent bonds that extends throughout a
crystalline structure
Giant molecule of many repeating units
Very hard, high M.P., generally nonconductors
3. Examples


Diamond: hard, does not conduct
Graphite: formed into sheets, used as lubricant,
conducts
13.8 OTHER KINDS OF SOLID
MATERIALS
13.8 OTHER KINDS OF SOLID
MATERIALS

B. Molecular solids

1. Particles and forces of attraction


2. Properties


Molecules are held together in a crystal structure by
intermolecular forces (all types)
Low to moderate MP and BP; soft; poor conductivity
3. Examples

H2O, C6H12O6, CO2
13.8 OTHER KINDS OF SOLID
MATERIALS

C. Amorphous Solids

1. Particles and forces of attraction



2. Properties


Covalent networks with no specific arrangements;
irregular
Shape can be changed somewhat easily
Noncrystalline; wide range of MP; poor conductivity
3. Examples

Glass, Polyethylene, Nylon
13.9 THE PHYSICAL
PROPERTIES OF SOLIDS
1. Continuum of strengths of bonds
Ionic > Metallic > Network Cov > Covalent > H-Bonding > Dipole-Dipole > Dispersion
13.10 PHASE DIAGRAMS

Graph that shows what phase of matter (solid,
liquid, gas) a substance will be in under conditions
of Temp and Pressure
13.10 PHASE DIAGRAMS

1. Know the location of the following on a phase
diagram: gas, liquid, and solid areas, triple
point, critical T and P, normal bp, relative
densities of solid and liquid. See Diagrams.
13.10 PHASE DIAGRAMS

2. Ex13.6 A pure substance has a vapor pressures of 320.mmHg at
125oC, 800.mmHg at 150.oC, and 60.0mmHg at the triple point, 85.0oC.
The melting point of the substance increases slightly as pressure
increases. Sketch the phase diagram for this substance. Estimate the
normal boiling point of the substance. What changes occur as the
temperature drops from 150.0oC to 100.0oC at a constant pressure of
320.mmHg?
13.10 PHASE DIAGRAMS

Phase diagram of CO2