New Jersey Center for Teaching and Learning
Slide 1 / 90
Progressive Science Initiative
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Intermolecular Forces,
Liquids, and Solids
www.njctl.org
Slide 3 / 90
Table of Contents
Click on the topic to go to that section
· States of Matter
· Properties of Gases
· Measuring Pressure
· Gas Laws
· Ideal Gas Law
· Gas Density
· Partial Pressure
· Graham's Law of Effusion
· Real versus Ideal Gases
Slide 4 / 90
States of Matter
Return to
Table of
Contents
Slide 5 / 90
So far this year….
We first explained atoms, and how to build up the periodic table
from quantum numbers.
Then we explained how atoms combine to form molecules: the
most common way we find most atoms in nature, and learned
about how atoms from molecules rearrange in chemical
reactions to form new chemical compounds.
Now, we're going to use intermolecular forces to combine
molecules to create the common states of matter.
Slide 6 / 90
Intermolecular Forces
Intermolecular forces are the piece we need to add to the
puzzle to explain the world around us.
Without intermolecular forces, we wouldn't have tables, lakes,
wall...or even our bodies.
Intermolecular forces shape our world.
Slide 7 / 90
States of Matter
While there are many states of matter, the three common states
that dominate our world are gases, liquids and solids.
These are the states of matter we'll be studying.
We won't be discussing more exotic states such as plasma,
nuclear matter, etc.
Slide 8 / 90
States of Matter
The 2 fundamental differences between states of matter are:
the distance between particles
the particles' freedom to move
Slide 9 / 90
States of Matter
Gas
cool or
increase
pressure
heat or
decrease
pressure
Particles are far apart,
total freedom,
much of empty space,
total disorder
Liquid
Crystalline solid
cool
heat
disorder, freedom,
free to move relative
to each other,
close together
ordered arrangement,
particles are in fixed
positions,
close together
Slide 10 / 90
Solid
Liquid
Gas
Enjoy this musical interlude by
They Might Be Giants!
Characteristics of the States of Matter
Slide 11 / 90
Gas
SHAPE
Assumes the shape of its container
VOLUME
Expands to the volume of its container
Is compressible
COMPRESSION
Flows easily
FLOW
Very Rapid
DIFFUSION
Characteristics of the States of Matter
Liquid
SHAPE
Assumes the shape of the part of a
container it occupies
VOLUME
Does not expand to the volume
of the container
COMPRESSION
Is virtually incompressible
FLOW
Flows easily
DIFFUSION
Within a liquid, slow
Slide 12 / 90
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Characteristics of the States of Matter
Solid
SHAPE
Retains its own shape
regardless of container
VOLUME
Does not expand to the
volume of its container
COMPRESSION
Is virtually incompressible
Does not flow
FLOW
Within a solid,
very very slow
DIFFUSION
Slide 14 / 90
Condensed Phases
In the solid and liquid states particles are closer together, we
refer to them as condensed phases.
Gas
Liquid
cool or
increase
pressure
cool
heat
heat or
decrease
pressure
Particles are far apart,
total freedom,
much of empty space,
total disorder
Crystalline solid
disorder, freedom,
free to move relative
to each other,
close together
ordered arrangement,
particles are in fixed
positions,
close together
Slide 15 / 90
A
It fills only a portion of its container.
B
Its molecules are in relatively rigid positions.
C
It takes on the shape of its entire container.
D
It is not compressible.
E
Diffusion is very slow within it.
Answer
1 Which of the below is a characteristic of a
gas?
Slide 15 (Answer) / 90
1 Which of the below is a characteristic of a
gas?
A
It fills only a portion of its container.
B
Its molecules are in relatively rigid positions.
It takes on the shape of its entire container.
D
It is not compressible.
E
Diffusion is very slow within it.
Answer
C
C
[This object is a pull
tab]
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2 Which of the below is a characteristic of a
liquid?
B
It fills only a portion of its container.
Its molecules are in relatively rigid positions.
C
It takes on the shape of its entire container.
D
It is compressible.
E
Diffusion is very rapid within it.
2 Which of the below is a characteristic of a
liquid?
A
B
It fills only a portion of its container.
Its molecules are in relatively rigid positions.
It takes on the shape of its entire container.
D
It is compressible.
E
Diffusion is very rapid within it.
Answer
C
A
[This object is a pull
tab]
Answer
A
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3 Which of the below is a characteristic of a
solid?
It fills all of its container.
B
Its molecules are in relatively rigid positions.
C
It takes on the shape of its entire container.
D
It is compressible.
E
Diffusion is very rapid within it.
Answer
A
3 Which of the below is a characteristic of a
solid?
It fills all of its container.
B
Its molecules are in relatively rigid positions.
C
It takes on the shape of its entire container.
D
E
Answer
A
It is compressible.
Slide 17 (Answer) / 90
B
Diffusion is very rapid within it.
[This object is a pull
tab]
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States of Matter
The state of a substance at a particular temperature
and pressure depends on two opposing properties:
Intermolecular Forces, which pulls them together
Kinetic energy of the particles, which pulls them apart
Without intermolecular forces (IMF's), all molecules would
be ideal gases...there would be no liquids or solids.
Intermolecular Forces & Boiling Points
Slide 19 / 90
Boiling represents a transition from a liquid to a gas.
To make that transition, molecules in the liquid must break free
of the intermolecular forces that bind them.
Intermolecular Forces & Boiling Points
The kinetic energy of the molecules
is proportional to the temperature:
as temperature rises, so does
kinetic energy.
Slide 20 / 90
Water molecules
overcome their
intermolecular
forces at 100 C.
The boiling point refers to the
temperature at which the molecules'
energy overcomes the
intermolecular forces binding them
together.
The higher the boiling point of a
substance, the stronger the
intermolecular forces.
Intermolecular Forces
H
Cl
Covalent bond
(strong)
H
Cl
Intermolecular
attraction ( weak)
The attractions between molecules, intermolecular
forces, are not nearly as strong as the intramolecular
attractions that hold compounds together.
They are, however, strong enough to control physical
properties such as boiling and melting points, vapor
pressures, and viscosities.
Slide 21 / 90
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Intermolecular Forces
There are three types of Intermolecular Forces:
they are sometimes called van der Waals Forces
Dipole-dipole interactions
Hydrogen bonding
London dispersion forces (LDF's)
Dipole-Dipole Interactions
A dipole is a polar molecule.
The interaction between
any two like charges is
repulsive (black)
+
Molecules that have permanent
dipoles are attracted to each
other.
+
-
-
-
The positive end of one is
attracted to the negative end of
the other and vice-versa.
-
+
These forces are only important
when the molecules are close to
each other.
Slide 23 / 90
-
+
+
+
The interaction between any
two opposite charges is
attractive ( red)
Only polar molecules will have this type
of Intermolecular Force.
Dipole-Dipole Interactions
The polarity of a molecule is measured by its dipole moment, m .
The more polar the molecule, the greater its dipole moment.
The more polar the molecule, the higher its boiling point.
That's because the attraction between the dipoles holds the
molecules together, not letting them boil away.
Substance
Molecular
Weight
(amu)
Acetonitrile, CH3CN
Acetaldehyde, CH3CHO
Methyl chloride, CH3Cl
Dimethyl ether, CH3OCH3
Propane, CH3CH2CH3
41
44
50
46
44
Dipole
Moment
u(D)
3.9
2.7
1.9
1.3
0.1
Boiling
Point
(k)
355
294
249
248
231
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A
B
C
D
E
CH3CH2CH3
Molecular Dipole
Substance Wt.
Moment
CH3OCH3
CH3CH2CH3 44
0.1
CH3Cl
CH3CHO
CH3OCH3 46
1.3
CH3CN
CH3Cl
50
1.9
CH3CHO
CH3CN
44
41
Answer
4 Which of the below molecules will have the
highest boiling point?
2.7
3.9
Slide 26 / 90
CH3CH2CH3
B CH3OCH3
C CH3Cl
A
D
CH3CHO
E
CH3CN
Substance
Molecular Dipole
Moment
Wt.
CH3CH2CH3
44
46
50
44
41
CH3OCH3
CH3Cl
CH3CHO
CH3CN
0.1
1.3
1.9
2.7
3.9
Answer
5 Which of the below molecules will have the
lowest boiling point?
Slide 27 / 90
London Dispersion Forces
London Dispersion Forces occur between all molecules.
They result from the fact that electrons are in constant motion
and sometimes are the same side of the molecule.
When they are on one side, the molecule is polarized: one side
is negative and the other is positive; the molecule acts like a
dipole.
δ-
-
δ+
Slide 28 / 90
London Dispersion Forces
That polarization creates an electric field that oppositely
polarizes nearby molecules...leading to an attraction.
δ-
δ-
δ+
-
δ+
-
Slide 29 / 90
London Dispersion Forces
While the electrons in helium repel each other, they
occasionally wind up on the same side of the atom.
At that instant, the helium atom is polar, with an
excess of electrons on one side and a shortage on the other.
e2+
e-
δ-
Helium atom
δ+
London Dispersion Forces
Another helium atom nearby, has a dipole induced in it, as the electrons
on the left side of the first atom repel the electrons in the second.
electrostatic attraction
e-
e2+
2+
e-
e-
Helium atom 1 Helium atom 2
London dispersion forces, or dispersion forces, are attractions between an
instantaneous dipole and an induced dipole.
δ-
δ+
δ-
δ+
Slide 30 / 90
Slide 31 / 90
Polarizability
These forces are present in all molecules, whether they are
polar or nonpolar.
The tendency of an electron cloud to distort in this way is
called polarizability.
Because larger molecules have more electrons, they are
more polarizable. Molecules with more electrons experience
stronger London Dispersion Forces.
Slide 32 / 90
6 Molecules with more electrons experience stronger
London Dispersion Forces.
True
Answer
False
6 Molecules with more electrons experience stronger
London Dispersion Forces.
True
Answer
False
True
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London Dispersion Forces
Examine the trends among the halogens and the noble gases:
Number Boiling
Noble
Halogen of
Point
gas
electrons (K)
F2
Cl2
Br2
I2
18
34
70
106
85.1 He
238.6 Ne
332.0
457.6
Ar
Kr
Xe
Number
Boiling
of
point (K)
electrons
2
10
18
36
54
4.6
27.3
87.5
120.9
166.1
the greater the number of electrons,
the more polarizable the particles are,
resulting in stronger London dispersion forces.
Slide 34 / 90
7 Which of the following molecules will have the
highest boiling point?
Answer
A F2
B Cl2
C Br2
D I2
7 Which of the following molecules will have the
highest boiling point?
B Cl2
C Br2
Answer
A F2
D
D I2
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tab]
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A
F2
B
Cl2
C
Br2
D
I2
Answer
8 Which of the below molecules will have the
lowest boiling point?
Slide 35 (Answer) / 90
8 Which of the below molecules will have the
lowest boiling point?
F2
B
Cl2
Answer
A
Br2
C
D
A
I2
[This object is a pull
tab]
A
He
B
Ne
C
Ar
D
Kr
E
Xe
Answer
9 Which of the below molecules will have the highest
boiling point?
Slide 36 / 90
9 Which of the below molecules will have the highest
boiling point?
He
B
Ne
C
Ar
D
Kr
E
Xe
Answer
A
Slide 36 (Answer) / 90
E
[This object is a pull
tab]
10 Which of the below molecules will have the lowest
boiling point?
B
C
D
E
He
Ne
Answer
A
Ar
Kr
Xe
10 Which of the below molecules will have the lowest
boiling point?
A
He
Ne
Answer
B
C
D
E
Slide 37 / 90
Ar
A
Kr
Xe
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tab]
Slide 37 (Answer) / 90
Slide 38 / 90
Which Have a Greater Effect?
Dipole-Dipole Interactions or Dispersion Forces
Dipole-Dipole
If two polar molecules
are of comparable
size, dipole-dipole
interactions are the
dominating force.
Dispersion Forces
If one molecule is much
larger than another,
dispersion forces will likely
determine its physical
properties.
If molecules are nonpolar,
dispersion forces will
dominate, since all molecules
experience dispersion forces.
Slide 39 / 90
Hydrogen Bonding
The graph shows the boiling
points for four polar and four
non-polar compounds.
For the non-polar series,
(CH4 to SnH4 ), boiling points
increase with higher number
of electrons. There are
stronger dispersion forces due
to greater polarizability.
Hydrogen Bonding
Examine the boiling points for the
four polar compounds (4,2,2 =
bent) called Group 16 hydrides.
For this series from H2 S through
H2 Te, boiling points increase with
increasing polarity as expected.
Recall that greater differences in
electronegativities make a bond
more polar.
What is going on with water?
It would be expected to have the lowest BP in the group, but
instead has the highest boliing point.
Slide 40 / 90
Slide 41 / 90
Hydrogen Bonding
The dipole-dipole interactions
experienced when H is bonded to
N, O, or F are unusually strong.
We call these interactions
hydrogen bonds.
Hydrogen Bonding
Slide 42 / 90
Hydrogen bonding arises in part from the high electronegativity
and small radius of nitrogen, oxygen, and fluorine.
When hydrogen is bonded to one of those very electronegative
elements, the hydrogen nucleus is exposed.
F
F
Click here to watch an animation about Hydrogen Bonding
Hydrogen Bonding
Ice is the only solid that floats in
its liquid form.
If it didn't, life on Earth would be
very different. For instance,
lakes would freeze from the
bottom and fish couldn't survive winters.
Hydrogen bonding creates the
space in ice that explains its low density.
Click here to watch an animation
of the Water - Ice transition
Slide 43 / 90
Slide 44 / 90
A
HF
B
HCl
C
HBr
Answer
11 Which of the following molecules has hydrogen
bonding as one of its intermolecular forces?
D
HI
E
All of the above.
Slide 44 (Answer) / 90
11 Which of the following molecules has hydrogen
bonding as one of its intermolecular forces?
HF
B
HCl
C
HBr
D
HI
E
All of the above.
Answer
A
A
[This object is a pull
tab]
Slide 45 / 90
A
B
CH3F
CH3Cl
C
HBr
D
NO2
E
None of the above.
Answer
12 Which of the following molecules has
hydrogen bonding as one of its IM forces?
Slide 45 (Answer) / 90
12 Which of the following molecules has
hydrogen bonding as one of its IM forces?
CH3F
CH3Cl
A
Answer
B
C
HBr
D
NO2
E
A
None of the above.
[This object is a pull
tab]
Slide 46 / 90
Ion-Dipole Interactions
There is a fourth molecular force that will be important as we
explore solutions later this year: Ion-dipole interactions are not
considered a van der Waals force.
The strength of these forces are what make it possible for
ionic substances to dissolve in polar solvents.
+
-
+
-
-
+
+
+
-
_
+
+
-
-
-
+
-
+
Anion- dipole attractions
Cation -dipole attractions
Slide 47 / 90
Summary of Interactions
Interacting
molecules or ions
Are polar
molecules involved?
NO
NO
Are ions involved?
YES
YES
Are polar
molecules and ions
both present?
YES
NO
Are hydrogen
atoms bonded to
N,O,or F atoms?
NO
YES
Dispersion
Dipole-dipole
forces only
forces
Hydrogen bonding
(induced dipoles) H S, CH Cl
2
3
H2O, NH3
Ar, I2
van der Waals forces
Ion- dipole forces
NaCl in H2O
Click here to watch a summary of IMF
Ionic bonding
NaCl, KI
Slide 48 / 90
Summary of IMF
London
dispersion
forces
Dipole- dipole
Hydrogenbonding
medium strength
IMF
strongest IMF
Who has it?
ALL molecules
have this IMF.
Nonpolar
molecules have
ONLY this IMF.
Only POLAR
molecules
Only POLAR
molecules with a
H atom covalently
bonded to N, O, or
F
How do you tell
who has it?
Molecules are
nonpolar if:
· · · · · · · it is
diatomic, or
· · · · · · · last
VSEPR number is
zero
Molecules are polar if:
· · · · · · · it's made of ONLY
2 different
atoms, or
· · · · · · · Last
VSEPR number is
non-zero (except 642,
523 are NONpolar)
What if there is a
tie within a
category?
Look at # of
electrons
Look at the dipole
moment (given)
Comparison of
weakest IMF
strength
See above
Look at which
molecule has
more N-H, O-H, or
F-H bonds
Slide 49 / 90
A
PH3
B
H 2S
C
HCl
D
SiH4
E
None of the above.
Answer
13 Which of the following molecules has London
dispersion as its only IM force?
A
PH3
B
H 2S
C
HCl
D
SiH4
E
None of the above.
D
[This object is a pull
tab]
Answer
13 Which of the following molecules has London
dispersion as its only IM force?
Slide 49 (Answer) / 90
Slide 50 / 90
14 How many of these substances will have dipoledipole interactions? (How many are polar
molecules?)
0
B
1
C
2
D
3
E
4
H 2O
CO2
CH4
NH3
Answer
A
Slide 50 (Answer) / 90
14 How many of these substances will have dipoledipole interactions? (How many are polar
molecules?)
0
B
1
C
2
D
3
E
4
H 2O
Answer
A
CO2
CH4
NH3
C
[This object is a pull
tab]
Slide 51 / 90
A
H 2O
B
CO2
C
CH4
D
NH3
Answer
15 Which of the following molecules will have the
highest boiling point?
Slide 51 (Answer) / 90
15 Which of the following molecules will have the
highest boiling point?
H 2O
B
CO2
Answer
A
C
D
CH4
A
NH3
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Slide 52 / 90
16 Of the following diatomic molecules,
which has the highest boiling point?
N2
B
Br2
C
H2
D
Cl2
E
O2
Answer
A
16 Of the following diatomic molecules,
which has the highest boiling point?
A
Br2
Answer
B
N2
C
H2
D
Cl2
E
O2
B
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tab]
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Slide 53 / 90
17 Of the following diatomic molecules, which has
the lowest boiling point?
B
C
D
E
N2
Br2
Answer
A
H2
Cl2
O2
Slide 53 (Answer) / 90
17 Of the following diatomic molecules, which has
the lowest boiling point?
A
Answer
B
C
D
E
N2
Br2
H2
C
Cl2
O2
[This object is a pull
tab]
Slide 54 / 90
A
CBr4
B
CF4
C
CCl4
D
CI4
Answer
18 Which one of the following derivatives of methane
(CH4) has the lowest boiling point?
Slide 54 (Answer) / 90
18 Which one of the following derivatives of methane
(CH4) has the lowest boiling point?
A
CBr4
B
CF4
CCl4
D
CI4
Answer
C
B
[This object is a pull
tab]
Slide 55 / 90
19 Which one of the following derivatives of
methane (CH4) has the highest boiling point?
CBr4
B CF4
C CCl4
D CI4
Answer
A
Slide 55 (Answer) / 90
19 Which one of the following derivatives of
methane (CH4) has the highest boiling point?
CBr4
CF4
C CCl4
D CI4
A
Answer
B
D
[This object is a pull
tab]
Intermolecular Forces Affect Many
Physical Properties
Slide 56 / 90
The strength of the attractions
between particles can greatly
affect the properties of a
substance or solution.
Slide 57 / 90
Viscosity
Resistance of a liquid to flow is called viscosity.
It is related to the ease with which molecules can move past each
other. Viscosity increases with stronger intermolecular forces and
decreases with higher temperature.
Substance
Hexane
Heptane
Octane
Nonane
Decane
Formula
Viscosity ( kg/m-s)
CH3CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
3.26 x 10-4
4.09 x 10-4
5.42 x 10-4
7.11 x 10-4
1.42 x 10-3
Surface Tension
Surface tension results from the net inward force
experienced by the molecules on the surface of a liquid.
Slide 58 / 90
Slide 59 / 90
Phase Changes
GAS
Vaporization
Condensation
Energy of system
Sublimation
Deposition
LIQUID
Melting
Freezing
SOLID
Energy Changes Associated with
Changes of State
Slide 60 / 90
Chemical and physical changes are usually accompanied by
changes in energy.
When energy is put into the system, the process is called
endothermic.
When energy is released by the system, the process is called
exothermic.
20 Which of the following is not a phase change?
A
vaporization
B
effusion
C
melting
D
sublimation
Slide 61 / 90
Slide 62 / 90
Boiling vs. Evaporation
Boiling and evaporation are two ways in which a liquid can
vaporize into a gas. However, there are important
distinctions between these processes.
Boiling
Evaporation
occurs at a specific
temperature, the boiling
point (B.P.)
occurs below the boiling
point
occurs throughout the
entire liquid
occurs only at the surface of
a liquid
achieved when atmospheric
pressure equals vapor
pressure (Patm = Pvap)
Slide 63 / 90
Vapor Pressure
Vapor pressure is defined as the pressure exerted by gas
molecules above the surface of an enclosed liquid.
(A)
(B)
Sample (A) at a lower
temperature shows some
vapor above the surface of
the liquid.
Sample (B) at a higher
temperature shows a greater
number of vapor particles, thus
resulting in higher vapor pressure.
Slide 64 / 90
Vapor Pressure
At any temperature some molecules in a liquid have
enough energy to escape.
As the temperature rises, the fraction of molecules that
have enough energy to escape increases.
Liquid - Vapor Equilibrium
liquid
becomes
gas
gas
becomes
liquid
Slide 65 / 90
As more molecules escape
the liquid, the pressure
they exert increases.
Eventually, the liquid and
vapor reach a state of
dynamic equilibrium: liquid
molecules evaporate and
vapor molecules condense
at the same rate.
Slide 66 / 90
Vapor Pressure Curve
Like any line, the curve is made up
of an infinite number of points.
Each point along the curve shows
the temperature at which
atmospheric pressure equals
vapor pressure
Patm = Pvap
In other words, each point along
the curve indicates a boiling point.
The type of graph shown here is called a
vapor pressure curve.
Vapor Pressure Curve
The boiling point of a liquid is the
temperature at which its vapor
pressure equals atmospheric
pressure.
The normal boiling point is the
temperature at which its vapor
pressure is 760 torr.
(AKA 760 mm Hg = 1 atm)
Slide 67 / 90
21 What is the normal boiling point of ethanol?
Slide 68 / 90
34.6
40.0
C
60.0
D
78.3
E
100.0
A
B
22 What is the boiling point ( in oC) of diethyl ether at 200 torr?
A
B
C
D
-10
0
760
35
23 What is the boiling point of water at 300 torr?
A
B
C
D
E
Slide 69 / 90
200
50
100
75
90
Slide 70 / 90
Pressure Cooking
Slide 71 / 90
A liquid will boil when its vapor
pressure equals atmospheric
pressure.
A pressure cooker works by
increasing the "atmospheric"
pressure inside it, so water will
not boil at 100oC; instead, it
may be heated up to 120oC
before turning to steam.
Raising the cooking temperature cuts cooking time drastically.
Pressure Cooking
Slide 72 / 90
www.washingtonpost.com
Slide 73 / 90
Boiling and Pressure
Recall that boiling occurs when Pvap = Patm
Since atmospheric pressure is so low
at high altitudes, (e.g. top of Mount
Everest) water will boil at a much lower
temperature than in New Jersey.
Click here for a video of
water boiling at
room temperature
Patm = 33 kPa on Mt. Everest
Patm = 101.3 kPa at sea level
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24 It will take longer to hard-boil an egg
(cooking time only)
A on top of Mt. Everest
B at sea level
C cooking times are equal
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Volatility
Volatility is another characteristic of a liquid that is based upon
the strength of its intermolecular forces.
The more volatile a liquid:
The more quickly it evaporates
The higher its vapor pressure at a given temperature
The weaker its Intermolecular Forces
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Phase Diagrams
Phase diagrams display the state of a substance at various
pressures and temperatures and the places where equilibria
exist between phases.
Phase Diagrams
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The circled line is the liquid-vapor interface.
It starts at the triple point (T), the point at which all three
states are in equilibrium.
Phase Diagrams
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The liquid-vapor interface ends at the critical point (C);
above this critical temperature and critical pressure the
liquid and vapor are indistinguishable from each other.
Phase Diagrams
The circled line in the diagram below is the interface between
liquid and solid.
The melting point at each pressure can be found along this line.
Slide 79 / 90
Phase Diagrams
Slide 80 / 90
Below the triple point the substance cannot exist in the liquid
state.
Along the circled line the solid and gas phases are in equilibrium;
the sublimation point at each pressure is along this line.
Phase Diagram of Water
Slide 81 / 90
Note the high critical temperature
and critical pressure.
These are due to the strong van der
Waals forces between water
molecules.
Comparison of Two Phase Diagrams
For water, the slope of the
solid-liquid line is negative.
This means that an
increase in pressure can
cause this substance to
melt. Water is the only
substance that does this.
For carbon dioxide, the
slope of the solid-liquid line
is positive, as it is for most
other substances. This
means that an increase in
pressure can cause
substances to freeze.
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Phase Diagram of Carbon Dioxide
Slide 83 / 90
Carbon dioxide cannot exist in the liquid
state at pressures below 5.11 atm; CO2
sublimes at normal pressures.
The low critical temperature and critical
pressure for CO2 make supercritical CO2
a good solvent for extracting nonpolar
substances (like caffeine).
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Solids
We can think of solids as falling into two groups.
Crystalline, in which particles
are in highly ordered
arrangement.
Amorphous, in which there is
no particular order in the
arrangement of particles.
NDT Education Resource Center
Slide 85 / 90
Amorphous Solids
Some examples of amorphous solids are:
rubber, glass, paraffin wax and cotton candy.
Crystalline solids include ionic compounds, metals and another
group called covalent-network solids. Crystalline solids are
categorized by bonding type as shown on the next slide.
Types of Bonding in Crystalline Solids
Covalent-Network Solids: Diamond
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Slide 87 / 90
Diamonds are an example
of a covalent-network solid,
in which carbon atoms are
covalently bonded to four
other carbon atoms.
They tend to be hard and
have high melting points.
Covalent-Network Solids: Graphite
Graphite is another example
of a covalent-network solid.
Each carbon atom is
covalently bonded to 3 others
in layers of interconnected
hexagonal rings.
The layers are held together
by weak dispersion forces.
The layers slide easily across
one another, so graphite is
used as a lubricant as well as
the "lead" in pencils.
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Slide 89 / 90
Metallic Solids
Metals are not covalently bonded,
but the attractions between atoms
are too strong to be van der
Waals forces.
In metals, valence electrons are
delocalized throughout the solid.
This means that the "sea" of
electrons moves freely around all
the nuclei.
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click here for an animation about
metallic bonding
Properties of Metallic Solids
The delocalized nature of the electrons
in metals accounts for many physical
properties.
For example, metals are generally:
good conductors of heat and electricity
malleable
ductile, (i.e. may be drawn into wires)
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