Chapter 13: Bonding and Molecular Structures: Intermolecular Forces, Liquids, and Solids
Chapter 13 Problem Set
Pages 633-639
2, 3, 6, 16, 22, 24, 26, 30, 32, 37, 55, 58, 62
Most elements are solids.
13.1 STATES OF MATTER AND THE KINETIC MOLECULAR THEORY
The kinetic molecular theory of gases assumes that gas particles are widely separated and that their
properties can be described by…
But
liquids and solids are more complicated
13.2 INTERMOLECULAR FORCES
Intermolecular forces are directly related to properties such as melting point, boiling point
How do the strength of intermolecular forces compare to intramolecular forces?
Interactions Between Ions and Molecules with a Permanent Dipole
What factors affect the strength of the interaction between an ion and a molecule with a permanent
dipole?
1.
2.
3.
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What is the energy of hydration?
Account for the trend in the enthalpy of hydration of the alkali metal cations.
EXAMPLE 13.1 Page 588 Hydration Energy
Explain why the enthalpy of hydration of Na+ (-405 kJ/mol) is somewhat more negative than that of
Cs + (-263 kJ/mol), whereas that of Mg2+ is much more negative (-1922 kJ/mol) than that of either Na+
or Cs+.
EXERCISE 13.1 Page 588 Hydration Energy
Which should have the more negative enthalpy of hydration F-, or Cl- ? Explain briefly
Interactions Between Molecules with Permanent Dipoles
What happens when two polar molecules meet each other?
What is the enthalpy of vaporization?
What is meant by the statement, “like dissolves like”?
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Why are water and ethanol miscible with each other, whereas water and octane are immiscible?
Hydrogen Bonding
Water, hydrogen fluoride, and ammonia have unusually high boiling points.
There are two reasons that hydrogen bonds are stronger than ordinary dipole forces.
1. The electronegativity difference between hydrogen and fluoride, oxygen, or nitrogen is quite large.
2. The small size of hydrogen allows the unshared electron pair of F, O, or N atom of one molecule to
approach the H atom in another very closely.
EXAMPLE 13.2 Page 592 The Effect of Hydrogen Bonding
Ethanol, CH3CH2OH, and dimethyl ether, CH3OCH3, have the same formula but a different
arrangement of atoms (they are isomers). Predict which of these compounds has the higher boiling
points.
How can O2 molecules dissolve in a polar substance like water?
Dispersion Forces: Interactions Involving Induced Dipoles
Dispersion forces are found in all molecular substances. What are dispersion forces?
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Interactions Between Polar and Nonpolar Molecules
What is the biological oxygen demand (BOD)?
What is polarization?
The higher the molar masses the greater the polarizability of the molecule.
Interactions Between Nonpolar Molecules
An estimate of the intermolecular forces can be obtained from the heat of vaporization of the
substance at its boiling point.
The intermolecular force of attraction in liquids and solids composed of nonpolar molecules is
Page 597 Figure 13.3 GREAT RESOURCE!
EXAMPLE 13.3 Page 598 Intermolecular Forces
Decide what type of intermolecular force is involved in each of these examples, and place them in
order of increasing strength of interaction: (a) liquid methane, CH4; a mixture of water and methanol,
H2O and CH3OH; (c) a solution of lithium chloride, LiCl, in water
EXERCISE 13.2 Page 598 Intermolecular Forces
Decide what type of intermolecular force is involved in liquid oxygen, hydrated magnesium sulfate,
and oxygen dissolved in water. Place the interactions in order of increasing strength.
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13.3 PROPERTIES OF LIQUIDS
Of the three states of matter, liquids are the most complicated.
Enthalpy of Vaporization
Vaporization or evaporation is the process in which…
Vaporization is an endothermic process because…
Condensation is an exothermic process because…
The boiling point and Hvap of nonpolar liquids increase with increasing molar mass.
What is the trend for the heavier hydrogen halides?
EXAMPLE 13.4 Page 600 Enthalpy of Vaporization
You put 1.00 L of water (about 4 cupfuls) in a pan at 100 0C, and it slowly evaporates. How much heat
must have been supplied to vaporize the water?
EXERCISE 13.3 Page 602 Enthalpy of Vaporization
The molar enthalpy of vaporization of methanol is 35.2 kJ/mol at 64.6 0C. How much energy is
required to evaporate 1.00 kg of this alcohol ?
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Vapor Pressure
When the rate of evaporation equals the rate of condensation, a system is then in a state of…
The vapor pressure measured at the equilibrium point is called…
EXAMPLE 13.5 Page 604 Vapor Pressure
You place 2.00 L of water in your dormitory room, which has a volume of 4.33 x 104 L. You seal the
room and wait for the water to evaporate. Will all of the water evaporate at 25 0C? (At 25 0C the
density of water is 0.997 g/mL, and its vapor pressure is 23.8 mm Hg.)
EXERCISE 13.4 Page 604 Vapor Pressure Curves
Look at the vapor pressure curve for ethanol p 604.
a. What is the approximate vapor pressure of ethanol at 40 °C ?
b. Are liquid and vapor in equilibrium when the temp is 60 °C and the press is 600 mm Hg ? If not,
does liquid evaporate to form more vapor ?
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EXERCISE 13.5 Page 604 Vapor Pressure
If 0.50 g of pure water is sealed in an evacuated 5.0 L flask and the whole assembly is heated to 60 °C,
will the pressure be equal to or less than the equilibrium vapor press of water at this temperature? What
if you use 2.0 g of water? Under either set of conditions is any liquid water left in the flask, or does all
of the water evaporate?
Boiling Point
The boiling point of a liquid is the temperature at which its vapor pressure is
Critical Temperature and Pressure
What is the critical temperature?
What is the critical pressure?
What are some characteristics of a supercritical fluid?
What is a practical use of supercritical CO2 ?
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Surface Tension, Capillary Action, and Viscosity
Molecules at the surface of a liquid behave differently from those in the interior.
What is surface tension?
What is capillary action?
What are adhesive and cohesive forces?
What is viscosity?
EXAMPLE 13.6 Page 609 Viscosity
Glycerol, HOCH2CHOHCH2OH is used in cosmetics. Do you expect it viscosity to be larger or
smaller than the viscosity of ethanol, CH3CH2OH ? Why or why not?
13.4 METALLIC AND IONIC SOLIDS
Page 610 Table 13.6 GREAT RESOURCE!
Crystal Lattices and Unit Cells of Metal Atoms
What is a unit cell?
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The “stoichiometry” of a solid is reflected by a unit cell.
Look at Figure 13.25 Page 611 which gives an idea of the structure based on a 2-d model. This is
needed to help understand the 3-d models. In the 2-d models all unit cells contain a net of 1 white
circle and 1 black circle.
What are lattice points?
Nature uses seven, three-dimensional unit cells. The simplest is a cubic unit cell.
Within the cubic class, there are three important cell symmetries…
Page 613 Figure 13.28
Primitive or simple cubic (sc) has 1 net particle within the unit cell
Body centered cubic (bcc) arrangement has a net of 2 particles within the unit cell.
Face centered cubic (fcc) arrangement has a net of four atoms or ions within the unit cell
To count the number of particles per unit cell, remember that one-eighth of each corner is actually a
unit cell, one-fourth of an edge atom is actually a unit cell, and one-half of a face particle is actually a
unit cell.
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EXAMPLE 13.6 Page 614 Determination of an Atomic Radius from Measurements of a Crystal
Lattice
Aluminum has a density of 2.699g/cm3, and the atoms are packed into a face-centered cubic unit cell.
Use this information to find the radius of an aluminum atom.
1. Find the mass of the unit cell
2. Combine the density of the metal with the mass of the unit call to find unit cell volume
3. Use the volume to find length of an edge of the unit cell
4. Calculate the radius of Al atom from the edge dimension
EXAMPLE 13.7 Page 615 The Structure of Iron
Iron has a density of 7.840 g/cm3, and the radius of an iron atom is 126 pm. Verify that the structure of
the solid is a body-centered cube.
bcc contains net of 2 atoms
1. Use atom radius to find length of an edge of the cube
2. Calculate the unit cell volume from the edge dimension
3. Combine the unit cell volume with the exp density to cals the mass of the unit cell
4. Compare the mass on 1 iron atom w/ the mass of the unit cell. The unit cell mass should be equal
to twice the mass of 1 Fe atom
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EXERCISE 13.7 Page 618 Determination of an Atomic Radius from Measurements of a Crystal
Lattice
Gold is a fcc unit cell. The density of the solid is 19.32 g/cm3. Calculate the radius of a gold atom.
Structures and Formulas of Ionic Solids
The packing of ions can be illustrated with LiCl. Here, the larger Cl ions form a face-centered cubic
lattice with the smaller Li ions fit into empty spaces between the Cl ions.
EXAMPLE 13.8 Page 619 Ionic Structure and Formula
One unit cell of the mineral perovskite is illustrated here. The compound is composed of Ca, Ti, and
O. Based on the unit cell, what is the formula of perovskite? What is the oxidation number of the Ti
atom?
EXERCISE 13.8 Page 619 Ionic Structure and Formula
Cesium chloride has a cubic unit cell of Cl- ions with Cs+ ions in the cubic holes. Prove that the
formula of the salt must have one Cs+ ion per Cl- ion.
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EXAMPLE 13.9 Page 620 Calculating the Density of an Ionic Compound from Unit Cell
Dimensions
MgO has a fcc unit cell of oxide ions with Mg ions in the octahedral holes. The radius of the Mg+2 ion
is 86 pm, and the radius of the O-2 is 126 pm. Calculate the density of MgO in g/cm3.
EXERCISE 13.9 Page 621 Density from Unit Cell Dimensions
Potassium chloride, KCl, has the same crystal structure as NaCl. Using the ion sizes in Figure 8.14,
calculate the density of KCl.
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13.5 OTHER KINDS OF SOLID MATERIALS
Molecular Solids
In molecular solids, covalently bonded molecules are found at the lattice points.
Network Solids
Network solids are substances composed of networks of covalently bonded atoms.
What are some properties of network covalent solids?
Amorphous Solids
How do properties of amorphous solids compare with those of crystalline solids?
13.6 THE PHYSICAL PROPERTIES OF SOLIDS
The melting point of a solid is the temperature at which
The enthalpy of fusion is
Page 626 Table 13.7
What is the relationship between the magnitude of melting points and the enthalpies of fusion?
The melting point of a solid can covey a great deal of information.
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EXAMPLE 13.10 Page 629 Heat of Vaporization and Fusion
Rubbing alcohol, or 2-propanol, is an organic compound that freezes at -89.5 0C and boils at 82.3 0C.
What quantity of heat is required to melt 10.0 g of 2-propanol at -89.5 0C, heat the resulting liquid to
the boiling point, and then evaporate the liquid at this temperature? Required information is: Hfusion =
5.37 kJ/mol; specific heat capacity of liquid 2-propanol = 2.60 J/g.K; and Hvap = 39.85 kJ/mol
Break calculation into three steps
EXERCISE 13.10 Page 629 Heat of Fusion
Calculate the heat required to melt 100.0 g of water at its melting point. Compare this with the heat
required to melt 100.0 g of the hydrocarbon octane (C8H18, with a melting point = -56.8 0C; Hfusion =
20.62 kJ/mol). Is there a relation between the calculated heats and types of intermolecular forces
involved?
13.7 PHASE DIAGRAMS
Depending on the conditions of temperature and pressure, a substance will exist as either a solid,
liquid, or vapor
A phase diagram is a graph that shows the relationship between the 3 phases of matter at different
Temperatures and Pressures
Triple point
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