1 © 2006 brooks/cole - thomson chemistry and chemical reactivity 6th edition john c. kotz paul m....

11

© 2006 Brooks/Cole - Thomson

Chemistry and Chemical Reactivity 6th Edition

John C. Kotz Paul M. Treichel

Gabriela C. Weaver

CHAPTER 13

Intermolecular Forces, Liquids, and Solids

© 2006 Brooks/Cole Thomson

Lectures written by John Kotz

22


WHYWHY??

• Why is water usually a liquid and not a gas?

• Why does liquid water boil at such a high temperature for such a small molecule?

• Why does ice float on water?

• Why do snowflakes have 6 sides?

• Why is I2 a solid whereas Cl2 is a gas?

• Why are NaCl crystals little cubes?

33


Liquids, Solids Liquids, Solids & Intermolecular Forces& Intermolecular Forces

Chap. 13Chap. 13

Liquids, Solids Liquids, Solids & Intermolecular Forces& Intermolecular Forces

Chap. 13Chap. 13

44


Inter-Inter-moleculamolecular Forcesr Forces

Inter-Inter-moleculamolecular Forcesr Forces

Have studied Have studied INTRAINTRAmolecular molecular forces—the forces holding forces—the forces holding atoms together to form atoms together to form molecules.molecules.

Now turn to forces between Now turn to forces between molecules —molecules — INTERINTERmolecular forces. molecular forces.

Forces between molecules, Forces between molecules, between ions, or between between ions, or between molecules and ions.molecules and ions.

55


Ion-Ion ForcesIon-Ion Forcesfor comparison of for comparison of

magnitudemagnitude

Ion-Ion ForcesIon-Ion Forcesfor comparison of for comparison of

magnitudemagnitude

NaNa++—Cl—Cl-- in salt in salt

These are the These are the strongest forces.strongest forces.

Lead to solids with Lead to solids with high melting high melting temperatures.temperatures.

NaCl, mp = 800 NaCl, mp = 800 ooCC

MgO, mp = 2800 MgO, mp = 2800 ooCC

66


Covalent Bonding ForcesCovalent Bonding Forcesfor comparison of for comparison of

magnitudemagnitude

Covalent Bonding ForcesCovalent Bonding Forcesfor comparison of for comparison of

magnitudemagnitude

C–H, 413 kJ/molC–H, 413 kJ/mol

C=C, 610 kJ/molC=C, 610 kJ/mol

C–C, 346 kJ/molC–C, 346 kJ/mol

CN, 887 kJ/molCN, 887 kJ/mol

77


Attraction Between Attraction Between Ions and Permanent Ions and Permanent

DipolesDipoles


DipolesDipoles

Water is highly polar Water is highly polar and can interact and can interact with positive ions to with positive ions to give give hydratedhydrated ions in water.ions in water.

HH

water dipole

••

••

O-

+

88



DipolesDipoles


DipolesDipoles

Water is highly polar Water is highly polar and can interact and can interact with positive ions to with positive ions to give give hydratedhydrated ions in water.ions in water.

HH

water dipole

••

••

O-

+

99



DipolesDipoles


DipolesDipoles

Many metal ions are hydrated. Many metal ions are hydrated. This is the reason metal salts This is the reason metal salts dissolve in waterdissolve in water..

1010


Attraction between ions and dipole depends on Attraction between ions and dipole depends on ion chargeion charge and and ion-dipole distanceion-dipole distance..

Measured by ∆H for MMeasured by ∆H for Mn+n+ + H + H22O --> [M(HO --> [M(H22O)O)xx]]n+n+

-1922 kJ/mol-1922 kJ/mol -405 kJ/mol-405 kJ/mol -263 kJ/mol-263 kJ/mol


DipolesDipoles


DipolesDipoles

OH

H+

-• • • O

H

H+

-• • • O

H

H+

-• • •

Na+Mg2+

Cs+

1111


Dipole-Dipole Dipole-Dipole ForcesForces


Such forces bind molecules having Such forces bind molecules having permanent dipoles to one another.permanent dipoles to one another.

1212




Influence of dipole-dipole forces is seen in Influence of dipole-dipole forces is seen in the boiling points of simple molecules.the boiling points of simple molecules.

CompdCompd Mol. Wt.Mol. Wt. Boil Boil PointPoint

NN22 2828 -196 -196 ooCC

COCO 2828 -192 -192 ooCC

BrBr22 160160 59 59 ooCC

IClICl 162162 97 97 ooCC

1313


Hydrogen BondingHydrogen BondingHydrogen BondingHydrogen Bonding

A special form of dipole-dipole attraction, A special form of dipole-dipole attraction, which enhances dipole-dipole attractions.which enhances dipole-dipole attractions.

H-bonding is strongest when X and Y are H-bonding is strongest when X and Y are N, O, N, O, or For F

1414


H-Bonding Between H-Bonding Between Methanol and WaterMethanol and WaterH-Bonding Between H-Bonding Between Methanol and WaterMethanol and Water

H-bondH-bondH-bondH-bond--

++

--

1515


H-Bonding Between H-Bonding Between Two Methanol Two Methanol

MoleculesMolecules

H-Bonding Between H-Bonding Between Two Methanol Two Methanol

MoleculesMolecules

H-bondH-bondH-bondH-bond

--++

--

1616


H-Bonding Between H-Bonding Between Ammonia and WaterAmmonia and WaterH-Bonding Between H-Bonding Between Ammonia and WaterAmmonia and Water

H-bondH-bondH-bondH-bond

--

++ --

This H-bond leads to the formation of This H-bond leads to the formation of NHNH44

++ and OH and OH--

1717


Hydrogen Bonding in HHydrogen Bonding in H22OOHydrogen Bonding in HHydrogen Bonding in H22OO

H-bonding is especially H-bonding is especially strong in water strong in water becausebecause

• the O—H bond is very the O—H bond is very polarpolar

• there are 2 lone pairs there are 2 lone pairs on the O atomon the O atom

Accounts for many of Accounts for many of water’s unique water’s unique properties.properties.

1818



Ice has open Ice has open lattice-like lattice-like structure.structure.

Ice density is Ice density is < liquid.< liquid.

And so solid And so solid floats on floats on water.water.

Snow flake: www.snowcrystals.com

1919



Ice has open lattice-like structure.Ice has open lattice-like structure.

Ice density is < liquid and so solid floats on water.Ice density is < liquid and so solid floats on water.

One of the VERY few One of the VERY few substances where substances where solid is LESS DENSE solid is LESS DENSE than the liquid.than the liquid.

2020


A A consequeconseque

nce of nce of hydrogen hydrogen bondingbonding

2121


Hydrogen Bonding in HHydrogen Bonding in H22OOHydrogen Bonding in HHydrogen Bonding in H22OOH bonds ---> abnormally high specific heat capacity of water (4.184 H bonds ---> abnormally high specific heat capacity of water (4.184

J/g•K)J/g•K)

This is the reason water is used to put out fires, it is the reason This is the reason water is used to put out fires, it is the reason lakes/oceans control climate, and is the reason thunderstorms lakes/oceans control climate, and is the reason thunderstorms release huge energy.release huge energy.

2222


Hydrogen BondingHydrogen BondingHydrogen BondingHydrogen Bonding

H bonds leads to H bonds leads to abnormally high abnormally high boiling point of boiling point of water.water.

See Screen 13.7See Screen 13.7

2323


Boiling Points of Boiling Points of Simple Hydrogen-Simple Hydrogen-

Containing Containing CompoundsCompounds

Active Figure 13.8Active Figure 13.8

2424


Methane Methane HydrateHydrateMethane Methane HydrateHydrate

2525


Methane Methane ClathrateClathrate

2626


Hydrogen Bonding in Hydrogen Bonding in BiologyBiology


H-bonding is especially strong in biological H-bonding is especially strong in biological systems — such as DNA. systems — such as DNA.

DNA — helical chains of phosphate groups DNA — helical chains of phosphate groups and sugar molecules. Chains are helical and sugar molecules. Chains are helical because of tetrahedral geometry of P, C, because of tetrahedral geometry of P, C, and O.and O.

Chains bind to one another by specific Chains bind to one another by specific hydrogen bonding between pairs of Lewis hydrogen bonding between pairs of Lewis bases.bases.

——adenine with thymineadenine with thymine

——guanine with cytosineguanine with cytosine

2727


Portion of a Portion of a DNA chainDNA chain

Double helix Double helix of DNAof DNA

2828


Base-Pairing through H-Base-Pairing through H-BondsBonds

2929




3030


Double Double Helix of Helix of

DNADNA

Double Double Helix of Helix of

DNADNA

3131


Discovering the Double Discovering the Double HelixHelix

Discovering the Double Discovering the Double HelixHelix

James Watson James Watson and Francis and Francis Crick, 1953Crick, 1953

Rosalind Rosalind Franklin, 1920-Franklin, 1920-19581958

Maurice Wilkins, Maurice Wilkins, 1916 - 20041916 - 2004

3232




Hydrogen bonding and base pairing in DNA.Hydrogen bonding and base pairing in DNA.

See Screen 13.6See Screen 13.6

3333


FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES


How can non-polar molecules such as OHow can non-polar molecules such as O2 2 and Iand I22 dissolve in water? dissolve in water?

The water dipole The water dipole INDUCESINDUCES a a dipole in the Odipole in the O22 electric cloud. electric cloud.

Dipole-induced Dipole-induced dipoledipole

Dipole-induced Dipole-induced dipoledipole

3434




Solubility increases with mass the gasSolubility increases with mass the gas

3535




• Process of inducing Process of inducing a dipole is a dipole is polarizationpolarization

• Degree to which Degree to which electron cloud of an electron cloud of an atom or molecule atom or molecule can be distorted in can be distorted in its its polarizabilitypolarizability..

3636


IM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLES

Consider IConsider I22 dissolving dissolving in ethanol, in ethanol, CHCH33CHCH22OH.OH.

OH

-

+

I-I

R-

+

OH

+

-

I-I

R

The alcohol The alcohol temporarily temporarily creates or creates or INDUCESINDUCES a a dipole in Idipole in I22..

3737




Formation of a dipole in two nonpolar IFormation of a dipole in two nonpolar I22 molecules.molecules.

Induced dipole-Induced dipole-induced dipoleinduced dipoleInduced dipole-Induced dipole-induced dipoleinduced dipole

3838




The induced forces between IThe induced forces between I22 molecules are molecules are

very weak, so solid Ivery weak, so solid I22 sublimessublimes (goes from (goes from a solid to gaseous molecules).a solid to gaseous molecules).

3939




The magnitude of the induced dipole depends The magnitude of the induced dipole depends on the tendency to be distorted. on the tendency to be distorted.

Higher molec. weight ---> larger induced Higher molec. weight ---> larger induced dipoles.dipoles.

MoleculeMolecule Boiling Point Boiling Point ((ooC)C)

CHCH44 (methane) (methane) - 161.5- 161.5

CC22HH66 (ethane) (ethane) - 88.6 - 88.6

CC33HH88 (propane) (propane) - 42.1- 42.1

CC44HH1010 (butane) (butane) - 0.5- 0.5

4040


Boiling Points of Boiling Points of HydrocarbonsHydrocarbons

Note linear relation between bp and molar mass.

CHCH44

CC22HH66

CC33HH88

CC44HH1010

4141


Summary of Summary of Intermolecular ForcesIntermolecular Forces

Summary of Summary of Intermolecular ForcesIntermolecular Forces

• Ion-dipole forcesIon-dipole forces

• Dipole-dipole forcesDipole-dipole forces–Special dipole-dipole force: Special dipole-dipole force: hydrogen bondshydrogen bonds

• Forces involving nonpolar Forces involving nonpolar molecules: molecules: induced forcesinduced forces

4242


Intermolecular Forces Intermolecular Forces SummarySummary

4343


Intermolecular ForcesIntermolecular Forces

Figure 13.13Figure 13.13

4444


LiquidsLiquidsSection 13.5Section 13.5

LiquidsLiquidsSection 13.5Section 13.5

In a liquidIn a liquid•• molecules are in molecules are in

constant motionconstant motion

•• there are appreciable there are appreciable intermolec. forcesintermolec. forces

•• molecules close molecules close togethertogether

•• Liquids are almost Liquids are almost incompressibleincompressible

•• Liquids do not fill the Liquids do not fill the containercontainer

4545


LiquidsLiquids

The two key properties we need to describe The two key properties we need to describe are are EVAPORATIONEVAPORATION and its opposite— and its opposite—CONDENSATIONCONDENSATION

The two key properties we need to describe The two key properties we need to describe are are EVAPORATIONEVAPORATION and its opposite— and its opposite—CONDENSATIONCONDENSATION

break IM bonds

make IM bonds

Add energy

Remove energy

LIQUID VAPOR

<---condensation<---condensation

evaporation--->evaporation--->

4646


Liquids—Liquids—EvaporationEvaporation

To evaporate, molecules To evaporate, molecules must have sufficient must have sufficient energy to break IM forces.energy to break IM forces.

Breaking IM forces Breaking IM forces requires energy. The requires energy. The process of process of evaporation is evaporation is endothermicendothermic..

4747


Liquids—Liquids—Distribution of EnergiesDistribution of Energies

Distribution of Distribution of molecular molecular energies in a energies in a liquid.liquid.

KE is propor-KE is propor-tional to T.tional to T.

Distribution of Distribution of molecular molecular energies in a energies in a liquid.liquid.

KE is propor-KE is propor-tional to T.tional to T.

0

Nu

mb

er o

f m

olec

ule

s

Molecular energy

higher Tlower T

See Figure 13.14See Figure 13.14

Minimum energy req’d to break IM forces and evaporate

4848


Distribution of Energy in a Distribution of Energy in a LiquidLiquid

Figure 13.14

4949


LiquidsLiquids At higher T a much At higher T a much larger number of larger number of molecules has high molecules has high enough energy to enough energy to break IM forces and break IM forces and move from liquid to move from liquid to vapor state.vapor state.

High E molecules carry High E molecules carry away E. You cool away E. You cool down when sweating down when sweating or after swimming.or after swimming.

.

0

Num

ber

of m

olec

ules

Molecular energy

minimum energy neededto break IM forces and evaporate

higher Tlower T

5050


LiquidsLiquidsWhen molecules of liquid When molecules of liquid

are in the vapor state, are in the vapor state, they exert a they exert a VAPOR VAPOR PRESSUREPRESSURE

EQUILIBRIUM EQUILIBRIUM VAPOR VAPOR PRESSUREPRESSURE is the is the pressure exerted by a pressure exerted by a vapor over a liquid in a vapor over a liquid in a closed container when closed container when the the rate of evaporation rate of evaporation = the rate of = the rate of condensation.condensation.

5151


Measuring Equilibrium Measuring Equilibrium Vapor PressureVapor Pressure

Liquid in flask evaporates and exerts pressure on manometer.

Active Fig. 13.17Active Fig. 13.17

5252


Vapor PressureVapor PressureCD, Screen 13.9CD, Screen 13.9

5353


Equilibrium Vapor PressureEquilibrium Vapor PressureActive Figure 13.18Active Figure 13.18

5454


LiquidsLiquidsEquilibrium Vapor PressureEquilibrium Vapor Pressure

FIGURE 13.18:FIGURE 13.18: VP as a function of T.VP as a function of T.

1. The curves show all conditions of P and 1. The curves show all conditions of P and T where LIQ and VAP are in T where LIQ and VAP are in EQUILIBRIUMEQUILIBRIUM

2. The VP rises with T.2. The VP rises with T.

3. When VP = external P, the liquid boils.3. When VP = external P, the liquid boils.

This means that BP’s of liquids change This means that BP’s of liquids change with altitude.with altitude.

5555


Boiling LiquidsBoiling Liquids

Liquid boils when its vapor pressure equals atmospheric pressure.

Liquid boils when its vapor pressure equals atmospheric pressure.

5656


Boiling Point Boiling Point at Lower Pressureat Lower Pressure

When pressure is lowered, the vapor When pressure is lowered, the vapor pressure can equal the external pressure at pressure can equal the external pressure at

a lower temperature.a lower temperature.

5757


Consequences of Vapor Consequences of Vapor Pressure ChangesPressure Changes

When can cools, vp of water drops. When can cools, vp of water drops. Pressure in the can is less than that of Pressure in the can is less than that of

atmosphere, so can is crushed. atmosphere, so can is crushed.

5858


4. If external P = 760 mm Hg, T of boiling is the 4. If external P = 760 mm Hg, T of boiling is the

NORMAL BOILING POINTNORMAL BOILING POINT

5. VP of a given molecule at a given T depends 5. VP of a given molecule at a given T depends

on IM forces. Here the VP’s are in the orderon IM forces. Here the VP’s are in the order

C2H5H5C2 HH5C2 HH

wateralcoholether

increasing strength of IM interactions

extensiveH-bondsH-bonds

dipole-dipole

OOO

LiquidsLiquidsFigure 13.18: VP versus TFigure 13.18: VP versus T

5959


LiquidsLiquids

HEAT OF VAPORIZATIONHEAT OF VAPORIZATION is the heat is the heat req’d (at constant P) to vaporize the liquid.req’d (at constant P) to vaporize the liquid.

LIQ + heat ---> VAPLIQ + heat ---> VAP

Compd.Compd. ∆H∆Hvapvap (kJ/mol) (kJ/mol) IM ForceIM Force

HH22OO 40.7 (100 40.7 (100 ooC)C) H-bondsH-bonds

SOSO22 26.8 (-47 26.8 (-47 ooC)C) dipoledipole

XeXe 12.6 (-107 12.6 (-107 ooC)C) induced induced dipole dipole

6060


Equilibrium Vapor Pressure Equilibrium Vapor Pressure & the Clausius-Clapeyron & the Clausius-Clapeyron

EquationEquation

• Clausius-Clapeyron equation Clausius-Clapeyron equation

— used to find ∆H˚— used to find ∆H˚vapvap..

• The logarithm of the vapor The logarithm of the vapor

pressure P is proportional to pressure P is proportional to

∆H∆Hvaporiationvaporiation and to 1/T. and to 1/T.

• ln P = –(∆H˚ln P = –(∆H˚vapvap/RT) + C/RT) + C

ln

P2P1

= Hvap

R

1T1

- 1T2

6161


LiquidsLiquidsMolecules at surface behave differently than those in the interior.Molecules at surface behave differently than those in the interior.

Molecules at surface experience net INWARD Molecules at surface experience net INWARD force of attraction. force of attraction. This leads to This leads to SURFACE TENSIONSURFACE TENSION — the energy — the energy req’d to break the surface.req’d to break the surface.

6262


Surface TensionSurface Tension

SURFACE TENSIONSURFACE TENSION also leads to spherical also leads to spherical liquid droplets.liquid droplets.

SURFACE TENSIONSURFACE TENSION also leads to spherical also leads to spherical liquid droplets.liquid droplets.

6363


LiquidsLiquidsIntermolec. forces also lead to Intermolec. forces also lead to CAPILLARYCAPILLARY

action and to the existence of a concave action and to the existence of a concave meniscus for a water column.meniscus for a water column.

concavemeniscus

H2O in

glasstube

ADHESIVE FORCESbetween waterand glass

COHESIVE FORCESbetween watermolecules

6464


Capillary ActionCapillary Action

Movement of water up a piece of paper Movement of water up a piece of paper depends on H-bonds between Hdepends on H-bonds between H22O and O and the OH groups of the cellulose in the the OH groups of the cellulose in the paper.paper.

6565


Metallic and Ionic Metallic and Ionic SolidsSolids

Sections 13.6-8Sections 13.6-8

Metallic and Ionic Metallic and Ionic SolidsSolids

Sections 13.6-8Sections 13.6-8

6666


Types of SolidsTypes of SolidsTable 13.6Table 13.6

TYPETYPE EXAMPLEEXAMPLEFORCEFORCE

Ionic Ionic NaCl, CaFNaCl, CaF22, ZnS, ZnS Ion-ionIon-ion

MetallicMetallic Na, FeNa, Fe MetallicMetallic

MolecularMolecular Ice, IIce, I22 DipoleDipole

Ind. dipoleInd. dipole

NetworkNetwork DiamondDiamond ExtendedExtendedGraphiteGraphite covalentcovalent

6767


Network SolidsNetwork Solids

DiamondDiamond

GraphiteGraphite

6868


Network SolidsNetwork Solids

A comparison of diamond (pure carbon) A comparison of diamond (pure carbon) with silicon.with silicon.

6969


Properties of SolidsProperties of Solids

1. Molecules, atoms or 1. Molecules, atoms or ions locked into a ions locked into a

CRYSTAL LATTICECRYSTAL LATTICE2. Particles are CLOSE 2. Particles are CLOSE

togethertogether

3. STRONG IM forces3. STRONG IM forces

4. Highly ordered, rigid, 4. Highly ordered, rigid, incompressibleincompressible

ZnS, zinc sulfideZnS, zinc sulfide

7070


Crystal LatticesCrystal Lattices• Regular 3-D arrangements of equivalent Regular 3-D arrangements of equivalent

LATTICE POINTS in space.LATTICE POINTS in space.• Lattice points define Lattice points define UNIT CELLSUNIT CELLS

– smallest repeating internal unit that has the symmetry smallest repeating internal unit that has the symmetry characteristic of the solid. characteristic of the solid.

7171


Cubic Unit CellsCubic Unit Cells

All anglesare 90 degrees

All sidesequal length

There are 7 basic crystal systems, but we are There are 7 basic crystal systems, but we are

only concerned withonly concerned with CUBICCUBIC..

7272


Cubic Unit Cells of Cubic Unit Cells of MetalsMetalsFigure 13.27Figure 13.27

Simple cubic (SC)Simple cubic (SC) Body-Body-

centered centered cubic (BCC)cubic (BCC)

Face-Face-centered centered cubic (FCC)cubic (FCC)

7373


Cubic Unit Cells of Cubic Unit Cells of MetalsMetalsFigure 13.27Figure 13.27

7474


Units Cells for MetalsUnits Cells for Metals


7575


• E atom is at a corner of a unit cell and is shared among 8 unit cells.

• Each edge is shared with 4 cells• Each face is part of two cells.

Simple Cubic Unit Simple Cubic Unit CellCell


7676


Atom Packing in Unit Atom Packing in Unit CellsCells

Assume atoms are hard spheres and that crystals are built Assume atoms are hard spheres and that crystals are built by by PACKINGPACKING of these spheres as efficiently as possible. of these spheres as efficiently as possible.

7777


Atom Packing in Unit Atom Packing in Unit CellsCells

Assume atoms are hard spheres and that crystals are built Assume atoms are hard spheres and that crystals are built by by PACKINGPACKING of these spheres as efficiently as possible. of these spheres as efficiently as possible.

7878


Atom Packing in Unit CellsAtom Packing in Unit Cells

7979


Crystal Lattices—Crystal Lattices—Packing of Atoms or IonsPacking of Atoms or Ions

• FCC is more efficient FCC is more efficient

than either BC or SC.than either BC or SC.

• Leads to layers of Leads to layers of

atoms.atoms.

8080


Packing of C60 molecules. They are arranged at the lattice points of a FCC lattice.

Crystal Lattices—Crystal Lattices—Packing of Atoms or IonsPacking of Atoms or Ions

8181


Number of Atoms per Unit Number of Atoms per Unit CellCell

Unit Cell Type Unit Cell Type Net Number AtomsNet Number Atoms SC SC BCCBCC FCCFCC

112244

8282


Atom Sharing Atom Sharing at Cube Faces and Cornersat Cube Faces and Corners

Atom shared in corner --> 1/8 inside each unit cell

Atom shared in face --> 1/2 inside each unit cell

8383


Simple Ionic CompoundsSimple Ionic Compounds

Lattices of many simple ionic solids are built Lattices of many simple ionic solids are built by taking a SC or FCC lattice of ions of one by taking a SC or FCC lattice of ions of one type and placing ions of opposite charge in type and placing ions of opposite charge in the holes in the lattice.the holes in the lattice.

EXAMPLE:EXAMPLE: CsCl has a SC lattice of Cs CsCl has a SC lattice of Cs++ ions ions with Clwith Cl-- in the center. in the center.

8484


Simple Ionic CompoundsSimple Ionic Compounds

CsCl unit cell has a SC lattice of ClCsCl unit cell has a SC lattice of Cl-- ions with Cs ions with Cs++ in the center. in the center.

1 unit cell has 1 Cs1 unit cell has 1 Cs++ ion ion plusplus

(8 corners)(1/8 Cl(8 corners)(1/8 Cl-- per corner) = 1 net Cl per corner) = 1 net Cl-- ion. ion.

8585


Two Views of CsCl Unit Two Views of CsCl Unit CellCell

•Lattice can be SC lattice of Cl- with Cs+ in hole•OR SC lattice of Cs+ with Cl- in hole•Either arrangement leads to formula of 1 Cs+ and 1 Cl- per unit cell

8686


Simple Ionic Simple Ionic CompoundsCompounds

Salts with formula Salts with formula MX can have SC MX can have SC structure — but not structure — but not salts with formula salts with formula MXMX22 or M or M22XX

8787


NaCl ConstructionNaCl Construction

FCC lattice of Cl- with Na+ in holes

NaNa++ in in octahedral octahedral holesholes

8888


Octahedral Holes - FCC Octahedral Holes - FCC LatticeLattice

8989


The Sodium Chloride The Sodium Chloride LatticeLattice

NaNa++ ions are in ions are in OCTAHEDRALOCTAHEDRAL holes holes in a face-centered in a face-centered cubic lattice of Clcubic lattice of Cl-- ions.ions.

9090


Many common salts have FCC arrangements Many common salts have FCC arrangements of anions with cations in of anions with cations in OCTAHEDRAL OCTAHEDRAL HOLESHOLES — e.g., salts such as CA = NaCl — e.g., salts such as CA = NaCl

•• FCC lattice of anions ----> 4 AFCC lattice of anions ----> 4 A--/unit cell/unit cell

•• CC++ in octahedral holes ---> 1 C in octahedral holes ---> 1 C++ at center at center

+ [12 edges • 1/4 C+ [12 edges • 1/4 C++ per edge] per edge]

= 4 C= 4 C++ per unit cell per unit cell

The Sodium Chloride The Sodium Chloride LatticeLattice

9191


Comparing NaCl and Comparing NaCl and CsClCsCl

• Even though their formulas have one cation and one anion, the lattices of CsCl and NaCl are different.

• The different lattices arise from the fact that a Cs+ ion is much larger than a Na+ ion.

9292


Common Ionic SolidsCommon Ionic Solids

Titanium dioxide, Titanium dioxide, TiOTiO22

There are 2 net There are 2 net TiTi4+4+ ions and 4 ions and 4 net Onet O2- 2- ions per ions per unit cell.unit cell.

9393


Common Ionic SolidsCommon Ionic Solids• Zinc sulfide, ZnSZinc sulfide, ZnS

• The SThe S2-2- ions are in ions are in TETRAHEDRALTETRAHEDRAL holes in the Znholes in the Zn2+2+ FCC lattice.FCC lattice.

• This gives 4 net This gives 4 net ZnZn2+2+ ions and 4 ions and 4 net Snet S2-2- ions. ions.

9494


Common Ionic Common Ionic SolidsSolids

• Fluorite or CaF2

• FCC lattice of Ca2+ ions

• This gives 4 net Ca2+ ions.

• F- ions in all 8 tetrahedral holes.

• This gives 8 net F- ions.

9595


Barium titanate, a perovskite

Barium titanate, a perovskite

Ba2+

Ti4+

BaTiO3

9696


CommoCommon Ionic n Ionic SolidsSolids

Magnesium silicate, Magnesium silicate, MgSiOMgSiO33

9797


BiotiteBiotiteBiotiteBiotite•Layers of linked octahedra of MgO6 and FeO6.•Layers of linked SiO4 tetrahedra.•K ions between layers

9898


Phase DiagramsPhase Diagrams

9999


TRANSITIONS TRANSITIONS BETWEEN BETWEEN PHASESPHASESSection 13.10Section 13.10

Lines connect all conditions of T and P where Lines connect all conditions of T and P where EQUILIBRIUM exists between the phases on either side EQUILIBRIUM exists between the phases on either side of the line.of the line.

(At equilibrium particles move from liquid to gas as fast (At equilibrium particles move from liquid to gas as fast as they move from gas to liquid, for example.)as they move from gas to liquid, for example.)

100100


Phase Diagram for WaterPhase Diagram for Water

Solid phaseSolid phase

Liquid phaseLiquid phase

Gas phaseGas phase

101101


Phase Equilibria — WaterPhase Equilibria — WaterSolid-liquidSolid-liquid

Gas-Gas-LiquidLiquid

Gas-Gas-SolidSolid

102102


Triple Point Triple Point — Water— Water

At the At the TRIPLE POINTTRIPLE POINT all all three phases are in three phases are in equilibrium.equilibrium.

103103


Phases Phases Diagrams—Diagrams—

Important Points Important Points for Waterfor Water

T(˚C)T(˚C) P(mmHg)P(mmHg)

Normal boil point Normal boil point 100100 760760

Normal freeze pointNormal freeze point 00 760760

Triple point Triple point 0.00980.0098 4.58 4.58

104104


Critical T and PCritical T and P

.

LIQUID

GAS

Pcritical

Hig

h P

ress

ure

High Temperature

Tcritical

Note that linegoes straight up

Above critical T Above critical T no liquid exists no liquid exists no matter how no matter how high the high the pressure.pressure.

Above critical T Above critical T no liquid exists no liquid exists no matter how no matter how high the high the pressure.pressure.

As P and T increase, you finally reach the As P and T increase, you finally reach the

CRITICAL TCRITICAL T and and PP

105105


Critical T and PCritical T and PCOMPDCOMPD TTcc((ooC)C) PPcc(atm)(atm)

HH22OO 374374 218218

COCO22 3131 7373

CHCH44 -82-82 4646

Freon-12Freon-12 112112 4141(CCl(CCl22FF22))

Notice that TNotice that Tcc and P and Pcc depend on depend on

intermolecular forces.intermolecular forces.

106106


Solid-Liquid EquilibriaSolid-Liquid EquilibriaIn any system, if you increase P the In any system, if you increase P the DENSITYDENSITY will go will go

up. up.

Therefore — as P goes up, equilibrium favors phase Therefore — as P goes up, equilibrium favors phase

with the larger density (or with the larger density (or SMALLERSMALLER volume/gram).volume/gram).

Liquid HLiquid H22OOSolid HSolid H22OO

DensityDensity 1 g/cm1 g/cm33 0.917 g/cm0.917 g/cm33

cmcm33/gram/gram 11 1.091.09

LIQUID H2OICEfavored atlow P

favored athigh P


favored athigh P

107107


Solid-Liquid EquilibriaSolid-Liquid Equilibria

Raising the pressure at Raising the pressure at constant T causes constant T causes water to melt.water to melt.

The NEGATIVE SLOPE The NEGATIVE SLOPE of the S/L line is of the S/L line is unique to Hunique to H22O. O.

Almost everything Almost everything else has positive else has positive slope.slope.

SolidH2O

LiquidH2O

P

T

760mmHg

0 ÞC

Normalfreezingpoint


favored athigh P


favored athigh P

108108


Solid-Solid-Liquid Liquid

EquilibriaEquilibria

The behavior of water The behavior of water under pressure is an under pressure is an example of example of

LE CHATELIER’S LE CHATELIER’S PRINCIPLEPRINCIPLE

At Solid/Liquid At Solid/Liquid equilibrium, raising P equilibrium, raising P squeezes the solid. squeezes the solid.

It responds by going to It responds by going to phase with greater phase with greater density, i.e., the liquid density, i.e., the liquid phase.phase.

SolidH2O

LiquidH2O

P

T

760mmHg

0 ÞC

Normalfreezingpoint

109109


Solid-Vapor EquilibriaSolid-Vapor EquilibriaAt P < 4.58 mmHg and T < 0.0098 ˚CAt P < 4.58 mmHg and T < 0.0098 ˚C

solid Hsolid H22O can go directly to vapor. This O can go directly to vapor. This

process is called process is called SUBLIMATIONSUBLIMATION

This is how a frost-free refrigerator works.This is how a frost-free refrigerator works.

110110


COCO22 Phase Diagram Phase Diagram

111111


COCO22 Phases Phases

Separate phases

Increasing pressure

More pressure

Supercritcal CO2

Figure 13.41

1 © 2006 brooks/cole - thomson chemistry and chemical reactivity 6th edition john c. kotz paul m....

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