Principles of chemistry 3e by nivaldo j tro 1

iv 3 Molecules, Compounds, and Chemical Equations 76 10 Chemical Bonding II: Molecular Shapes, Valence Bond Theory, and 11 Liquids, Solids, and Intermolecular Forces 428 Appendix

The labels on top (1A, 2A, etc.) are common American usage The labels below these (1, 2, etc.) are those recommended

by the International Union of Pure and Applied Chemistry

Atomic masses in brackets are the masses of the longest-lived or most important isotope of radioactive elements.

*Element 117 is currently under review by IUPAC.

a Mass of longest-lived or most important isotope.

b The names of these elements have not yet been decided.

List of Elements with Their Symbols and Atomic Masses

Element Symbol NumberAtomic Atomic Mass

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Library of Congress Cataloging-in-Publication Data

Tro, Nivaldo J.

Principles of Chemistry : a molecular approach / Nivaldo J Tro, WestmontCollege Third edition.

p cm

ISBN 978-0-321-97194-4

1 Chemistry, Physical and theoretical Textbooks 2 Chemistry, Physical and theoretical Study and

teaching (Higher) I Title.

To Michael, Ali, Kyle, and Kaden

About the Author

Nivaldo Tro is a professor of chemistry at Westmont College

in Santa Barbara, California, where he has been a faculty member since 1990 He received his Ph.D in chemistry from Stanford University for work on developing and using optical techniques to study the adsorption and desorption of mole-cules to and from surfaces in ultrahigh vacuum He then went

on to the University of California at Berkeley, where he did postdoctoral research on ultrafast reaction dynamics in solu-tion Since coming to Westmont, Professor Tro has been awarded grants from the American Chemical Society Petroleum Research Fund, from the Research Corporation, and from the National Science Foundation to study

the dynamics of various processes occurring in thin adlayer films adsorbed on dielectric surfaces He has been

honored as Westmont’s outstanding teacher of the year three times and has also received the college’s

out-standing researcher of the year award Professor Tro lives in Santa Barbara with his wife, Ann, and their four children, Michael, Ali, Kyle, and Kaden In his leisure time, Professor Tro enjoys mountain biking, surfing, reading to his children, and being outdoors with his family

iv

3 Molecules, Compounds, and Chemical Equations 76

10 Chemical Bonding II: Molecular Shapes, Valence Bond Theory, and

11 Liquids, Solids, and Intermolecular Forces 428

Appendix I: Common Mathematical Operations in Chemistry A-1

Appendix IV: Answers to In-Chapter Practice Problems A-42

Brief Contents

Contents

1.2 The Scientific Approach to Knowledge 5

The States of Matter: Solid, Liquid, and Gas 7 Classifying

Matter According to Its Composition: Elements, Compounds,

and Mixtures 8

1.4 Physical and Chemical Changes and

1.5 Energy: A Fundamental Part of Physical and

The Standard Units 13 The Meter: A Measure of Length 14

The Kilogram: A Measure of Mass 14 The Second: A

Measure of Time 14 The Kelvin: A Measure of

Temperature 14 Prefix Multipliers 16 Derived Units: Volume

and Density 17 Volume 17 Density 18 Calculating

Density 18

Counting Significant Figures 21 Exact Numbers 22

Significant Figures in Calculations 23 Precision and

Accuracy 24

Converting from One Unit to Another 25 General

Problem-Solving Strategy 27 Units Raised to a Power 29

Problems Involving an Equation 30

Key Terms 33 Key Concepts 33 Key Equations and

Relationships 34 Key Learning Objectives 34

Problems by Topic 34 Cumulative Problems 38

Challenge Problems 39 Conceptual Problems 40

Questions for Group Work 41 Answers to Conceptual

Connections 41

2.1 imaging and Moving individual Atoms 43

2.2 Modern Atomic Theory and the laws

The Law of Conservation of Mass 45 The Law of Definite Proportions 46 The Law of Multiple Proportions 47 John Dalton and the Atomic Theory 48

Cathode Rays 49 Millikan’s Oil Drop Experiment:

The Charge of the Electron 50

2.5 Subatomic Particles: Protons, Neutrons, and

Elements: Defined by Their Numbers of Protons 53 Isotopes: When the Number of Neutrons Varies 54 Ions: Losing and Gaining Electrons 56

2.6 Finding Patterns: The Periodic law and

Ions and the Periodic Table 59

2.7 Atomic Mass: The Average Mass of an

2.8 Molar Mass: Counting Atoms by Weighing Them 62

The Mole: A Chemist’s “Dozen” 62 Converting between Number of Moles and Number of Atoms 63 Converting between Mass and Amount (Number of Moles) 64

Ionic Bonds 79 Covalent Bonds 80

3.3 representing Compounds: Chemical Formulas

Types of Chemical Formulas 80 Molecular Models 82

3.4 An Atomic-level view of Elements and Compounds 82

3.5 ionic Compounds: Formulas and Names 86

Writing Formulas for Ionic Compounds 87 Naming Ionic

Compounds 87 Naming Binary Ionic Compounds

Containing a Metal That Forms Only One Type of Cation 89

Naming Binary Ionic Compounds Containing a Metal That

Forms More Than One Kind of Cation 90 Naming Ionic

Compounds Containing Polyatomic Ions 91 Hydrated Ionic

Compounds 92

3.6 Molecular Compounds: Formulas and Names 93

Naming Molecular Compounds 93 Naming Acids 94

Naming Binary Acids 95 Naming Oxyacids 95

3.7 Formula Mass and the Mole Concept

Molar Mass of a Compound 97 Using Molar Mass

to Count Molecules by Weighing 97

Conversion Factors from Chemical Formulas 101

3.9 determining a Chemical Formula from

Calculating Molecular Formulas for

Compounds 104 Combustion Analysis 105

3.10 Writing and Balancing Chemical Equations 107

Writing Balanced Chemical Equations 109

3.11 organic Compounds 111

Key Terms 114 Key Concepts 114 Key Equations

and Relationships 115 Key Learning Objectives 116

Problems by Topic 117 Cumulative Problems 120

Challenge Problems 121 Conceptual Problems 122

Questions for Group Work 122 Answers to Conceptual

Connections 122

4.1 Climate Change and the Combustion of Fossil Fuels 125

4.2 reaction Stoichiometry: How Much

Making Pizza: The Relationships Among Ingredients 127 Making Molecules: Mole-to-Mole Conversions 128 Making Molecules: Mass-to-Mass Conversions 128

4.3 limiting reactant, Theoretical Yield, and

Limiting Reactant, Theoretical Yield, and Percent Yield from Initial Reactant Masses 133

4.4 Solution Concentration and Solution Stoichiometry 137

Solution Concentration 138 Using Molarity in Calculations 139 Solution Stoichiometry 143

4.5 Types of Aqueous Solutions and Solubility 144

Electrolyte and Nonelectrolyte Solutions 145 The Solubility

of Ionic Compounds 146

4.7 representing Aqueous reactions: Molecular, ionic,

4.8 Acid–Base and Gas-Evolution reactions 154

Acid–Base Reactions 154 Gas-Evolution Reactions 157

5.1 Breathing: Putting Pressure to Work 177

5.2 Pressure: The result of Molecular Collisions 178

Pressure Units 179

Contents vii

5.3 The Simple Gas laws: Boyle’s law, Charles’s law,

Boyle’s Law: Volume and Pressure 181 Charles’s Law:

Volume and Temperature 183 Avogadro’s Law: Volume and

Amount (in Moles) 185

5.5 Applications of the ideal Gas law: Molar volume,

Molar Volume at Standard Temperature and Pressure 189

Density of a Gas 189 Molar Mass of a Gas 191

5.6 Mixtures of Gases and Partial Pressures 192

Collecting Gases over Water 196

5.7 Gases in Chemical reactions: Stoichiometry

Molar Volume and Stoichiometry 200

5.8 Kinetic Molecular Theory: A Model for Gases 201

The Nature of Pressure 202 Boyle’s Law 202 Charles’s

Law 202 Avogadro’s Law 202 Dalton’s Law 202

Temperature and Molecular Velocities 203

5.9 Mean Free Path, diffusion, and

5.10 real Gases: The Effects of Size and intermolecular

The Effect of the Finite Volume of Gas Particles 207 The Effect

of Intermolecular Forces 208 Van der Waals Equation 209

Key Terms 210 Key Concepts 210 Key Equations and

Relationships 211 Key Learning Objectives 211

Problems by Topic 212 Cumulative Problems 215

Challenge Problems 217 Conceptual Problems 218

Questions for Group Work 218 Answers to Conceptual

Connections 219

6.2 The Nature of Energy: Key definitions 222

Units of Energy 224

6.3 The First law of Thermodynamics: There is

Internal Energy 225

Heat 230 Thermal Energy Transfer 232 Work:

6.7 Constant-Pressure Calorimetry: Measuring 𝚫Hrxn 242

6.8 Hess’s law and other relationships

The Wave Nature of Light 265 The Electromagnetic Spectrum 267 Interference and Diffraction 268 The Particle Nature of Light 270

7.3 Atomic Spectroscopy and the Bohr Model 273

7.4 The Wave Nature of Matter: The de Broglie Wavelength, the Uncertainty Principle, and indeterminacy 275

The de Broglie Wavelength 276 The Uncertainty Principle 277 Indeterminacy and Probability Distribution Maps 279

viii Contents

Trends in First Ionization Energy 325 Exceptions to Trends in First Ionization Energy 328 Trends in Second and

Successive Ionization Energies 328

8.8 Electron Affinities and Metallic Character 329

Electron Affinity 329 Metallic Character 330

Solutions to the Schrödinger Equation for the Hydrogen

Atom 281 Atomic Spectroscopy Explained 285

(l=2) 291 f Orbitals (l=3) 292 The Phase of

Orbitals 292 The Shapes of Atoms 292

Key Terms 293 Key Concepts 294 Key Equations and

Relationships 294 Key Learning Objectives 295

Problems by Topic 295 Cumulative Problems 296

Challenge Problems 297 Conceptual Problems 298

Questions for Group Work 298 Answers to Conceptual

Connections 298

8.2 The development of the Periodic Table 302

8.3 Electron Configurations: How Electrons

Electron Spin and the Pauli Exclusion Principle 304

Sublevel Energy Splitting in Multielectron Atoms 304

Electron Spatial Distributions and Sublevel Splitting 306

Electron Configurations for Multielectron Atoms 308

8.4 Electron Configurations, valence Electrons, and the

Orbital Blocks in the Periodic Table 312 Writing an

Electron Configuration for an Element from Its Position in

the Periodic Table 313 The Transition and Inner Transition

8.7 ions: Electron Configurations, Magnetic Properties,

ionic radii, and ionization Energy 321

Electron Configurations and Magnetic Properties of

Ions 321 Ionic Radii 322 Ionization Energy 325

9.3 representing valence Electrons with dots 344

9.4 ionic Bonding: lewis Symbols and

Ionic Bonding and Electron Transfer 345 Lattice Energy: The Rest of the Story 346 Trends in Lattice Energies: Ion Size 347 Trends in Lattice Energies: Ion Charge 347 Ionic Bonding: Models and Reality 348

9.5 Covalent Bonding: lewis Structures 349

Single Covalent Bonds 349 Double and Triple Covalent Bonds 350 Covalent Bonding: Models and Reality 350

9.6 Electronegativity and Bond Polarity 351

Electronegativity 352 Bond Polarity, Dipole Moment, and Percent Ionic Character 353

9.7 lewis Structures of Molecular Compounds and

Writing Lewis Structures for Molecular Compounds 356 Writing Lewis Structures for Polyatomic Ions 357

Resonance 358 Formal Charge 360

9.9 Exceptions to the octet rule: odd-Electron Species, incomplete octets, and Expanded octets 363

Odd-Electron Species 363 Incomplete Octets 363 Expanded Octets 364

Contents ix

10.8 Molecular orbital Theory: Electron delocalization 409

Linear Combination of Atomic Orbitals (LCAO) 410 Period Two Homonuclear Diatomic Molecules 413

9.10 Bond Energies and Bond lengths 365

Bond Energy 366 Using Average Bond Energies to Estimate

Enthalpy Changes for Reactions 367 Bond Lengths 369

9.11 Bonding in Metals: The Electron Sea Model 370

Key Terms 372 Key Concepts 372 Key Equations and

Relationships 373 Key Learning Objectives 373

Problems by Topic 373 Cumulative Problems 375

Challenge Problems 376 Conceptual Problems 377

Questions for Group Work 377 Answers to Conceptual

Connections 377

Molecular Shapes, valence

Bond Theory, and Molecular

10.1 Artificial Sweeteners: Fooled by Molecular Shape 379

10.2 vSEPr Theory: The Five Basic Shapes 380

Two Electron Groups: Linear Geometry 381 Three Electron

Groups: Trigonal Planar Geometry 381 Four Electron

Groups: Tetrahedral Geometry 381 Five Electron Groups:

Trigonal Bipyramidal Geometry 382 Six Electron Groups:

Octahedral Geometry 383

10.3 vSEPr Theory: The Effect of lone Pairs 384

Four Electron Groups with Lone Pairs 384 Five Electron

Groups with Lone Pairs 386 Six Electron Groups with

Lone Pairs 387

10.4 vSEPr Theory: Predicting Molecular Geometries 388

Representing Molecular Geometries on Paper 391

Predicting the Shapes of Larger Molecules 391

10.5 Molecular Shape and Polarity 392

10.6 valence Bond Theory: orbital overlap as a

10.7 valence Bond Theory: Hybridization of

sp3 Hybridization 399 sp2 Hybridization and Double

Bonds 400 sp Hybridization and Triple Bonds 404 sp3d

and sp3d2 Hybridization 405 Writing Hybridization and

Changes between States 432

11.3 intermolecular Forces: The Forces That Hold

Dispersion Force 433 Dipole–Dipole Force 435 Hydrogen Bonding 437 Ion–Dipole Force 439

11.4 intermolecular Forces in Action: Surface Tension,

Surface Tension 441 Viscosity 441 Capillary Action 442

11.5 vaporization and vapor Pressure 442

The Process of Vaporization 442 The Energetics of Vaporization 443 Heat of Vaporization 444 Vapor Pressure and Dynamic Equilibrium 445 Temperature Dependence of Vapor Pressure and Boiling Point 447 The Clausius–Clapeyron Equation 448 The Critical Point: The Transition to an Unusual State of Matter 450

Sublimation 451 Fusion 452 Energetics of Melting and Freezing 452

The Major Features of a Phase Diagram 454 Regions 454 Lines 455 The Triple Point 455 The Critical Point 455 Navigation within a Phase Diagram 456

x Contents

11.9 Water: An Extraordinary Substance 456

11.10 Crystalline Solids: Unit Cells and Basic Structures 457

Closest-Packed Structures 461

11.11 Crystalline Solids: The Fundamental Types 463

Molecular Solids 464 Ionic Solids 464 Atomic

Solids 465

11.12 Crystalline Solids: Band Theory 467

Key Terms 469 Key Concepts 469 Key Equations and

Relationships 470 Key Learning Objectives 471

Problems by Topic 471 Cumulative Problems 475

Challenge Problems 476 Conceptual

Problems 476 Questions for Group Work 477 Answers

to Conceptual Connections 477

12.1 Thirsty Solutions: Why You Should Not drink

12.2 Types of Solutions and Solubility 481

Nature’s Tendency toward Mixing: Entropy 481 The Effect

of Intermolecular Forces 482

12.3 Energetics of Solution Formation 485

Aqueous Solutions and Heats of Hydration 486

12.4 Solution Equilibrium and Factors Affecting

The Temperature Dependence of the Solubility of

Solids 489 Factors Affecting the Solubility of Gases in

Water 490

12.5 Expressing Solution Concentration 492

Molarity 493 Molality 494 Parts by Mass and Parts by

Volume 494 Mole Fraction and Mole Percent 495

12.6 Colligative Properties: vapor Pressure lowering,

Freezing Point depression, Boiling Point Elevation,

Vapor Pressure Lowering 498 Vapor Pressures of Solutions

Containing a Volatile (Nonelectrolyte) Solute 501 Freezing

Point Depression and Boiling Point Elevation 502

13.1 Catching lizards 519

13.2 The rate of a Chemical reaction 520

13.3 The rate law: The Effect of Concentration on

The Half-Life of a Reaction 533

13.5 The Effect of Temperature on reaction rate 536

Arrhenius Plots: Experimental Measurements of the Frequency Factor and the Activation Energy 538 The Collision Model: A Closer Look at the Frequency Factor 541

13.6 reaction Mechanisms 542

Rate Laws for Elementary Steps 542 Rate-Determining Steps and Overall Reaction Rate Laws 543 Mechanisms with a Fast Initial Step 544

Contents xi

Problems by Topic 552 Cumulative Problems 557

Challenge Problems 559 Conceptual Problems 560

Questions for Group Work 561 Answers to Conceptual

Connections 561

14.1 Fetal Hemoglobin and Equilibrium 563

14.2 The Concept of dynamic Equilibrium 565

14.3 The Equilibrium Constant (K) 566

Expressing Equilibrium Constants for Chemical

Reactions 567 The Significance of the Equilibrium

Constant 568 Relationships between the Equilibrium

Constant and the Chemical Equation 569

14.4 Expressing the Equilibrium Constant in Terms

Units of K 572

14.5 Heterogeneous Equilibria: reactions involving

14.6 Calculating the Equilibrium Constant from

Measured Equilibrium Concentrations 574

14.7 The reaction Quotient: Predicting the direction

14.8 Finding Equilibrium Concentrations 579

Finding Equilibrium Concentrations When We Are Given the

Equilibrium Constant and All but One of the Equilibrium

Concentrations of the Reactants and Products 579

15.2 The Nature of Acids and Bases 604

15.3 definitions of Acids and Bases 605

The Arrhenius Definition 606 The Brønsted–Lowry Definition 606

Finding Equilibrium Concentrations When We Are Given the Equilibrium Constant and Initial Concentrations or Pressures 580 Simplifying Approximations in Working Equilibrium Problems 584

14.9 le Châtelier’s Principle: How a System at Equilibrium responds to disturbances 588

The Effect of a Concentration Change on Equilibrium 588 The Effect of a Volume (or Pressure) Change on

Equilibrium 590 The Effect of a Temperature Change on Equilibrium 591

15.4 Acid Strength and the Acid ionization

Strong Acids 608 Weak Acids 609 The Acid Ionization

Constant (Ka) 610

The pH Scale: A Way to Quantify Acidity and Basicity 613

pOH and Other p Scales 615

15.6 Finding the [H 3 o∙] and pH of Strong and

Strong Acids 616 Weak Acids 616 Polyprotic Acids 620 Percent Ionization of a Weak Acid 622

Strong Bases 624 Weak Bases 624 Finding the [OH-]and pH of Basic Solutions 626

15.8 The Acid–Base Properties of ions and Salts 627

Anions as Weak Bases 628 Cations as Weak Acids 631

Classifying Salt Solutions as Acidic, Basic, or Neutral 632

15.9 Acid Strength and Molecular Structure 634

Binary Acids 634 Oxyacids 635

15.10 lewis Acids and Bases 636

Molecules That Act as Lewis Acids 637 Cations That Act

as Lewis Acids 638

Key Terms 639 Key Concepts 639 Key Equations and

Relationships 640 Key Learning Objectives 640

Problems by Topic 640 Cumulative Problems 643

Challenge Problems 644 Conceptual Problems 645

Questions for Group Work 645 Answers to Conceptual

Connections 645

16.1 The danger of Antifreeze 647

16.2 Buffers: Solutions That resist pH Change 648

Calculating the pH of a Buffer Solution 650

The Henderson–Hasselbalch Equation 651 Calculating pH

Changes in a Buffer Solution 654 The Stoichiometry

Calculation 654 The Equilibrium Calculation 655 Buffers

Containing a Base and Its Conjugate Acid 657

16.3 Buffer Effectiveness: Buffer range and

Relative Amounts of Acid and Base 659 Absolute

Concentrations of the Acid and Conjugate

Base 659 Buffer Range 660 Buffer Capacity 661

16.4 Titrations and pH Curves 662

The Titration of a Strong Acid with a Strong Base 663

The Titration of a Weak Acid with a Strong Base 666

The Titration of a Weak Base with a Strong Acid 672

The Titration of a Polyprotic Acid 672 Indicators:

pH-Dependent Colors 673

16.5 Solubility Equilibria and the Solubility

Ksp and Molar Solubility 675 Ksp and Relative

Solubility 677 The Effect of a Common Ion on

Solubility 677 The Effect of pH on Solubility 679

16.6 Precipitation 680

16.7 Complex ion Equilibria 681

17.1 Nature’s Heat Tax: You Can’t Win and You

17.2 Spontaneous and Nonspontaneous Processes 695

17.3 Entropy and the Second law of Thermodynamics 696

Entropy 697 The Entropy Change Associated with a Change in State 702

17.4 Heat Transfer and Changes in the Entropy of the

The Temperature Dependence of ∆Ssurr 704 Quantifying Entropy Changes in the Surroundings 704

17.5 Gibbs Free Energy 706

The Effect of ∆H, ∆S, and T on Spontaneity 708

17.6 Entropy Changes in Chemical reactions:

17.8 Free Energy Changes for Nonstandard States: The relationship between 𝚫G∙rxn and 𝚫Grxn 719

The Free Energy Change of a Reaction Under Nonstandard Conditions 720 Standard Conditions 720 Equilibrium Conditions 721 Other Nonstandard Conditions 721

17.9 Free Energy and Equilibrium: relating 𝚫G∙rxn to the

Contents xiii

Key Terms 725 Key Concepts 726 Key Equations and

Relationships 726 Key Learning Objectives 727

Problems by Topic 727 Cumulative Problems 730

Challenge Problems 731 Conceptual Problems 732

Questions for Group Work 732 Answers to Conceptual

Connections 733

18.1 Pulling the Plug on the Power Grid 735

18.2 Balancing oxidation–reduction Equations 736

18.3 voltaic (or Galvanic) Cells: Generating Electricity from

Electrochemical Cell Notation 741

18.4 Standard Electrode Potentials 742

Predicting the Spontaneous Direction of an Oxidation–

Reduction Reaction 747 Predicting Whether a Metal Will

Dissolve in Acid 749

18.5 Cell Potential, Free Energy, and

The Relationship between ∆G° and E°cell 750

The Relationship between E°cell and K 751

18.6 Cell Potential and Concentration 753

Concentration Cells 756

18.7 Batteries: Using Chemistry to Generate Electricity 757

Dry-Cell Batteries 757 Lead–Acid Storage Batteries 758

Other Rechargeable Batteries 758 Fuel Cells 759

18.8 Electrolysis: driving Nonspontaneous Chemical

Stoichiometry of Electrolysis 763

18.9 Corrosion: Undesirable redox reactions 764

Preventing Corrosion 766

Key Terms 767 Key Concepts 767 Key Equations and

Relationships 768 Key Learning Objectives 769

Problems by Topic 769 Cumulative Problems 772

Challenge Problems 773 Conceptual Problems 774

Questions for Group Work 774 Answers to Conceptual

19.3 The valley of Stability: Predicting the Type of

Magic Numbers 785 Radioactive Decay Series 785

19.4 The Kinetics of radioactive decay and

The Integrated Rate Law 787 Radiocarbon Dating: Using Radioactivity to Measure the Age of Fossils and

Artifacts 788 Uranium>Lead Dating 790

19.5 The discovery of Fission: The Atomic Bomb and

Nuclear Power: Using Fission to Generate Electricity 793

19.6 Converting Mass to Energy: Mass defect and

Mass Defect 795

19.7 Nuclear Fusion: The Power of the Sun 797

19.8 The Effects of radiation on life 798

Acute Radiation Damage 798 Increased Cancer Risk 798 Genetic Defects 798 Measuring Radiation Exposure 798

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To the Student

As you begin this course, I invite you to think about your

reasons for enrolling in it Why are you taking general

chemistry? More generally, why are you pursuing a college

education? If you are like most college students taking

gen-eral chemistry, part of your answer is probably that this

course is required for your major and that you are pursuing

a college education so you can get a good job someday

While these are good reasons, I suggest a better one I think

the primary reason for your education is to prepare you to

live a good life You should understand chemistry—not for

what it can get you—but for what it can do for you

Understanding chemistry, I believe, is an important source

of happiness and fulfillment Let me explain

Understanding chemistry helps you to live life to its

full-est for two basic reasons The first is intrinsic: Through an

understanding of chemistry, you gain a powerful appreciation

for just how rich and extraordinary the world really is The

second reason is extrinsic: Understanding chemistry makes

you a more informed citizen—it allows you to engage with

many of the issues of our day In other words, understanding

chemistry makes you a deeper and richer person and makes

your country and the world a better place to live These

rea-sons have been the foundation of education from the very

beginnings of civilization

How does chemistry help prepare you for a rich life and

conscientious citizenship? Let me explain with two examples

My first one comes from the very first page of Chapter 1 of

this book There, I ask the following question: What is the

most important idea in all of scientific knowledge? My

answer to that question is this: The properties of matter are

determined by the properties of molecules and atoms That

simple statement is the reason I love chemistry We humans

have been able to study the substances that compose the world

around us and explain their behavior by reference to particles

so small that they can hardly be imagined If you have never

realized the remarkable sensitivity of the world we can see to

the world we cannot, you have missed out on a fundamental

truth about our universe To have never encountered this truth

is like never having read a play by Shakespeare or seen a

sculpture by Michelangelo—or, for that matter, like never

having discovered that the world is round It robs you of an

amazing and unforgettable experience of the world and the

human ability to understand it

My second example demonstrates how science literacy

helps you to be a better citizen Although I am largely

sympa-thetic to the environmental movement, a lack of science

lit-eracy within some sectors of that movement, and the resulting

anti-environmental backlash, creates confusion that impedes

real progress and opens the door to what could be

misin-formed policies For example, I have heard conservative

pun-dits say that volcanoes emit more carbon dioxide—the most

significant greenhouse gas—than does petroleum tion I have also heard a liberal environmentalist say that we have to stop using hairspray because it is causing holes in the ozone layer that will lead to global warming Well, the claim about volcanoes emitting more carbon dioxide than petroleum combustion can be refuted by the basic tools you will learn to use in Chapter 4 of this book We can easily show that volca-noes emit only 1/50th as much carbon dioxide as petroleum combustion As for hairspray depleting the ozone layer and thereby leading to global warming: The chlorofluorocarbons that deplete ozone have been banned from hairspray since

combus-1978, and ozone depletion has nothing to do with global warming anyway People with special interests or axes to grind can conveniently distort the truth before an ill-informed public, which is why we all need to be knowledgeable

So this is why I think you should take this course Not just to satisfy the requirement for your major, and not just to get a good job someday, but also to help you to lead a fuller life and to make the world a little better for everyone I wish you the best as you embark on the journey to understand the world around you at the molecular level The rewards are well worth the effort

To the Professor

First and foremost, thanks to all of you who adopted this book

in its first and second editions You helped to make this book successful and I am grateful beyond words Second, I have listened carefully to your feedback on the previous edition The changes you see in this edition are a direct result of your input, as well as my own experience in using the book in my general chemistry courses If you have acted as a reviewer or have contacted me directly, you are likely to see your sugges-tions reflected in the changes I have made The goal of this

edition remains the same: to present a rigorous and ble treatment of general chemistry in the context of relevance.

accessi-Teaching general chemistry would be much easier if all of our students had exactly the same level of preparation and ability But alas, that is not the case Even though I teach at a relatively selective institution, my courses are populated with students with

a range of backgrounds and abilities in chemistry The challenge

of successful teaching, in my opinion, is therefore figuring out how to instruct and challenge the best students while not losing those with lesser backgrounds and abilities My strategy has always been to set the bar relatively high, while at the same time providing the motivation and support necessary to reach the high bar That is exactly the philosophy of this book We do not have

to compromise away rigor in order to make chemistry accessible

to our students In this book, I have worked hard to combine rigor with accessibility—to create a book that does not dilute the con-tent, yet can be used and understood by any student willing to put

in the necessary effort

Preface

xvi Preface

Principles of Chemistry: A Molecular Approach is first a

student-oriented book My main goal is to motivate students

and get them to achieve at the highest possible level As we all

know, many students take general chemistry because it is a

requirement; they do not see the connection between

chemis-try and their lives or their intended careers Principles of

Chemistry: A Molecular Approach strives to make those

con-nections consistently and effectively Unlike other books,

which often teach chemistry as something that happens only

in the laboratory or in industry, this book teaches chemistry in

the context of relevance It shows students why chemistry is

important to them, to their future careers, and to their world

Second, Principles of Chemistry: A Molecular Approach

is a pedagogically-driven book In seeking to develop

prob-lem-solving skills, a consistent approach (Sort, Strategize,

Solve, and Check) is applied, usually in a two- or three-column

format In the two-column format, the left column shows the

student how to analyze the problem and devise a solution

strategy It also lists the steps of the solution, explaining the

rationale for each one, while the right column shows the

imple-mentation of each step In the three-column format, the left

column outlines a general procedure for solving an important

category of problems that is then applied to two side-by-side

examples This strategy allows students to see both the general

pattern and the slightly different ways in which the procedure

may be applied in differing contexts The aim is to help

stu-dents understand both the concept of the problem (through the

formulation of an explicit conceptual plan for each problem)

and the solution to the problem.

Third, Principles of Chemistry: A Molecular Approach is a

visual book Wherever possible, images are used to deepen the

student’s insight into chemistry In developing chemical

prin-ciples, multipart images help to show the connection between

everyday processes visible to the unaided eye and what atoms

and molecules are actually doing Many of these images have

three parts: macroscopic, molecular, and symbolic This

combi-nation helps students to see the relationships between the

for-mulas they write down on paper (symbolic), the world they see

around them (macroscopic), and the atoms and molecules that

compose that world (molecular) In addition, most figures are

designed to teach rather than just to illustrate They are rich with

annotations and labels intended to help the student grasp the

most important processes and the principles that underlie them

The resulting images contain significant amounts of

informa-tion but are also uncommonly clear and quickly understood

Fourth, Principles of Chemistry: A Molecular Approach is

a “big picture” book At the beginning of each chapter, a short

introduction helps students to see the key relationships between

the different topics they are learning Through focused and

concise narrative, I strive to make the basic ideas of every

chapter clear to the student Interim summaries are provided at

selected spots in the narrative, making it easier to grasp (and

review) the main points of important discussions And to make

sure that students never lose sight of the forest for the trees,

each chapter includes several Conceptual Connections, which

ask them to think about concepts and solve problems without

doing any math I want students to learn the concepts, not just

plug numbers into equations to churn out the right answer

Principles of Chemistry: A Molecular Approach is, lastly, a book that delivers the core of the standard chemistry curriculum, without sacrificing depth of coverage Through our research, we have determined the topics that most faculty do not teach and we have eliminated them When writing a brief book, the temptation

is great to cut out the sections that show the excitement and

rel-evance of chemistry; we have not done that here Instead, we

have cut out pet topics that are often included in books simply to satisfy a small minority of the market We have also eliminated extraneous material that does not seem central to the discussion The result is a lean book that covers core topics in depth, while still demonstrating the relevance and excitement of these topics

I hope that this book supports you in your vocation of teaching students chemistry I am increasingly convinced of the importance of our task Please feel free to email me with any questions or comments about the book

Nivaldo J Trotro@westmont.edu

What’s New in This Edition?

The third edition has been extensively revised and contains many more small changes than I can detail here Below is a list of the most significant changes from the previous edition

• More robust media components have been added, including

80 Interactive Worked Examples, 39 Key Concept Videos,

14 additional Pause & Predict videos, 33 PHET tions, and 5 new Mastering simulations with tutorials

simula-• Each chapter now has a 10–15 question multiple-choice end-of-chapter Self-Assessment Quiz Since many colleg-

es and universities use multiple-choice exams, and because standardized final exams are often multiple choice, stu-dents can use these quizzes to both assess their knowledge

of the material in the chapter and to prepare for exams These quizzes are also available on mobile devices

• Approximately 100 new end-of-chapter group work questions have been added to encourage small group work

in or out of the classroom

• Approximately 45 new end-of-chapter problems have been added

• New conceptual connections have been added and many from the previous edition have been modified In addition,

to support active, in class, learning, these questions are now available in Learning Catalytics

• All data have been updated to the most recent available See for example:

Section 1.7 The Reliability of a Measurement in which

the data in the table of carbon monoxide tions in Los Angeles County (Long Beach) have been updated

concentra-Figure 4.2 Carbon Dioxide Concentrations in the sphere is updated to include information through 2013

Atmo-Figure 4.3 Global Temperature is updated to include

in-formation through 2013

Figure 4.19 U.S Energy Consumption is updated to

in-clude the most recent available information

Preface xvii

• Many figures and tables have been revised for clarity See,

for example:

Figure 3.6 Metals Whose Charge Is Invariant in

Section 3.5 This replaces Table 3.2 Metals Whose

Charge Is Invariant from One Compound to Another

The weather map in Section 5.2 has been replaced, and

the caption for the weather map has been simplified

and linked more directly to the text discussion

Figure 7.3 Components of White Light has been

re-placed with a corrected image of light passing through

a prism

Figure 7.4 The Color of an Object and Figure 7.17 The

Quantum-Mechanical Strike Zone both have updated

photos

The orbital diagram figure in Section 7.5 Quantum

Mechanics and the Atom that details the various

princi-pal levels and sublevels has been replaced with an

up-dated version that is more student-friendly and easier

to navigate

Figure 8.2 Shielding and Penetration is modified so

that there is a clear distinction between parts a and b

Figure 10.15 Molecular Orbital Energy Diagrams for

Second-Row Homonuclear Diatomic Molecules now

has magnetic properties and valence electron

configu-ration information

Figure 12.10 Solubility and Temperature Data for

Na2SO4 have been deleted from the graph, and data

Ce2(SO4)3 have been added to the graph

Figure 13.11 Thermal Energy Distribution is modified

It is now noted in the caption that Ea is a constant and

does not depend on temperature; new notations have

also been added to the figure

Table 15.5 Acid Ionization Constants for Some

Mono-protic Weak Acids at 25 °C has been modified to

in-clude pKa values

The unnumbered photo of a fuel cell car in Section

18.1 Pulling the Plug on the Power Grid has been

re-placed with an updated image of a newer fuel cell car

•

In Section 10.5 and throughout Chapter 11, the use of elec-trostatic potential maps has been expanded See, for

ex-ample, Figures 11.6, 11.7, 11.9, and 11.10

• In Section 10.8 Molecular Orbital Theory: Electron

De-localization in the subsection on Linear Combination of

Atomic Orbitals (LCAO), a discussion of molecular orbital

electron configuration has been added

• New chapter-opening art, briefer introductory material,

and a new first section (11.1 Water, No Gravity) replace

Section 11.1

• In Section 13.4 The Integrated Rate Law: The Dependence

of Concentration on Time, the derivation to integrate the

differential rate law to obtain the first-order integrated rate

law is now shown in a margin note

•

Some new in-chapter examples have been added, includ-ing Example 4.14 WritSome new in-chapter examples have been added, includ-ing Equations for Acid–Base actions Involving a Weak Acid and Example 9.9 Drawing Resonance Structures and Assigning Formal Charge for Organic Compounds

Re-Acknowledgments

The book you hold in your hands bears my name on the cover, but I am really only one member of a large team that care-fully crafted this book Most importantly, I thank my editor, Terry Haugen, who has become a friend and colleague Terry

is a skilled and competent editor He has given me direction, inspiration, and most importantly, loads of support I am just

as grateful for my program manager, Jessica Moro, and ect manager, Beth Sweeten, who have worked tirelessly behind the scenes to bring this project to completion I con-tinue to be grateful for Jennifer Hart in her new role oversee-ing development Jennifer, your guidance and wisdom are central to the success of my projects, and I am eternally grate-ful I am also grateful to Caitlin Falco who helped with orga-nizing reviews, as well as numerous other tasks associated with keeping the team running smoothly I also thank Erin Mulligan, who has now worked with me on many projects Erin is an outstanding developmental editor who not only worked with me on crafting and thinking through every word but is now also a friend and fellow foodie I am also grateful

proj-to Adam Jaworski Adam has become a fantastic leader at Pearson and a friend to me Thanks also to Dave Theisen, who has been selling my books for 15 years and has become a great friend Dave, I appreciate your tireless efforts, your pro-fessionalism, and your in-depth knowledge of my work And

of course, I am continually grateful for Paul Corey, with whom I have now worked for over 14 years and a dozen books Paul is a man of incredible energy and vision, and it is

my great privilege to work with him Paul told me many years ago (when he first signed me on to the Pearson team) to dream big, and then he provided the resources I needed to make

those dreams come true Thanks, Paul I would also like to

thank my first editor at Pearson, Kent Porter-Hamann Kent and I spent many good years together writing books, and I continue to miss her presence in my work

I am also grateful to my marketing managers, Will Moore and Chris Barker, who have helped to develop a great market-ing campaign for my books and are all good friends I am deeply grateful to Gary Hespenheide for crafting the design of this text I would like to thank Beth Sweeten and the rest of the Pearson production team I also thank Francesca Monaco and her co-workers at CodeMantra I am a picky author and Francesca is endlessly patient and a true professional I am also greatly indebted to my copy editor, Betty Pessagno, for her dedication and professionalism, and to Lauren McFalls, for her exemplary photo research I owe a special debt of gratitude to Quade and Emiko Paul, who continue to make my

xviii Preface

ideas come alive in their art Thanks also to Derek Bacchus

for his work on the cover and with design

I would like to acknowledge the help of my colleagues

Allan Nishimura, Michael Everest, Kristi Lazar, Steve

Contakes, David Marten, and Carrie Hill, who have supported

me in my department while I worked on this book Double

thanks to Michael Everest for also authoring the Questions for

Group Work I am also grateful to those who have supported

me personally First on that list is my wife, Ann Her love

rescued a broken man fifteen years ago and without her, none

of this would have been possible I am also indebted to my

children, Michael, Ali, Kyle, and Kaden, whose smiling faces

and love of life always inspire me I come from a large Cuban

family whose closeness and support most people would envy

Thanks to my parents, Nivaldo and Sara; my siblings, Sarita,

Mary, and Jorge; my siblings-in-law, Nachy, Karen, and John;

my nephews and nieces, Germain, Danny, Lisette, Sara, and

Kenny These are the people with whom I celebrate life

I would like to thank all of the general chemistry students

who have been in my classes throughout my years as a

profes-sor at Westmont College You have taught me much about

teaching that is now in this book I would also like to express

my appreciation to Michael Tro, who also helped in

manu-script development, proofreading, and working new

prob-lems

Lastly, I am indebted to the many reviewers whose ideas

are embedded throughout this book They have corrected me,

inspired me, and sharpened my thinking on how best to teach

this subject we call chemistry I deeply appreciate their

com-mitment to this project Thanks also to Frank Lambert for

helping us all to think more clearly about entropy and for his

review of the entropy sections of the book Last but by no

means least, I would like to record my gratitude to Brian

Gute, Milton Johnston, Jessica Parr, and John Vincent whose

alertness, keen eyes, and scientific astuteness help make this

a much better book

reviewers

Patrice Bell, Georgia Gwinnett College

Sharmaine Cady, East Stroudsburg University

James Cleveland, Northeast State Community College

Chris Collinson, Rochester Institute of Technology

Charlie Cox, Stanford University

Brent Cunningham, James Madison University

Bridget Decker, University of Wyoming-Laramie

William Deese, Louisiana Tech University

Dawn Del Carlo, University of Northern Iowa

Steve Everly, Lincoln Memorial University

Daniel Finnen, Shawnee State University

Paul Fischer, Macalester College

David Geiger, The State University of New York (Geneseo)

Patricia Goodson, University of Wyoming

Burt Hollandsworth, Harding University

Matthew Horn, Utah Valley University

Mary Elizabeth Kinsel, Southern Illinois University

Gerald Korenowski, Rensselaer Polytechnic Institute

Hoitung Leung, University of Virginia

Clifford Padgett, Armstrong State University Andrew Price, Temple University

Jennifer Schwartz Poehlmann, Stanford University Anthony Smith, Walla Walla University

Thomas Sorensen, University of Wisconsin (Milwaukee) Kara Tierney, Monroe Community College

Rosie Walker, Metropolitan State University of Denver

Accuracy reviewers

Brian Gute, University of Minnesota, Duluth Milton Johnston, University of South Florida Jessica Parr, University of Southern California John Vincent, University of Alabama

Previous Edition reviewers

Patricia G Amateis, Virginia Tech T.J Anderson, Francis Marion University Paul Badger, Robert Morris University Yiyan Bai, Houston Community College Maria Ballester, Nova Southeastern University Rebecca Barlag, Ohio University

Shuhsien Batamo, Houston Community College (Central Campus)

Craig A Bayse, Old Dominion University Maria Benavides, University of Houston, Downtown Charles Benesh, Wesleyan College

Silas C Blackstock, University of Alabama Justin Briggle, East Texas Baptist University Ron Briggs, Arizona State University Katherine Burton, Northern Virginia Community College David A Carter, Angelo State University

Linda P Cornell, Bowling Green State University, Firelands Charles T Cox, Jr., Georgia Institute of Technology

David Cunningham, University of Massachusetts, Lowell Michael L Denniston, Georgia Perimeter College Ajit S Dixit, Wake Technical Community College David K Erwin, Rose-Hulman Institute of Technology Giga Geme, University of Central Missouri

Vincent P Giannamore, Nicholls State University Pete Golden, Sandhills Community College Robert A Gossage, Acadia University Susan Hendrickson, University of Colorado (Boulder) Angela Hoffman, University of Portland

Andrew W Holland, Idaho State University Narayan S Hosmane, Northern Illinois University Jason C Jones, Francis Marion University Jason A Kautz, University of Nebraska, Lincoln Chulsung Kim, Georgia Gwinnett College Scott Kirkby, East Tennessee State University Richard H Langley, Stephen F Austin State University Christopher Lovallo, Mount Royal College

Eric Malina, University of Nebraska, Lincoln David H Metcalf, University of Virginia Dinty J Musk, Jr., Ohio Dominican University Edward J Neth, University of Connecticut MaryKay Orgill, University of Nevada, Las Vegas

Preface xix

Gerard Parkin, Columbia University

BarJean Phillips, Idaho State University

Nicholas P Power, University of Missouri

Changyong Qin, Benedict College

William Quintana, New Mexico State University

Valerie Reeves, University of New Brunswick

Dawn J Richardson, Collin College

Thomas G Richmond, University of Utah

Melinda S Ripper, Butler County Community College

Jason Ritchie, The University of Mississippi

Christopher P Roy, Duke University

Jamie Schneider, University of Wisconsin (River Falls)

John P Scovill, Temple University

Thomas E Sorensen, University of Wisconsin, Milwaukee

Vinodhkumar Subramaniam, East Carolina University

Dennis Swauger, Ulster County Community College

Ryan Sweeder, Michigan State University

Chris Syvinski, University of New England

Dennis Taylor, Clemson University

David Livingstone Toppen, California State University,

Northridge

Harold Trimm, Broome Community College

Tommaso A Vannelli, Western Washington University

Kristofoland Varazo, Francis Marion University

Susan Varkey, Mount Royal College

Joshua Wallach, Old Dominion University

Clyde L Webster, University of California, Riverside

Wayne Wesolowski, University of Arizona Kurt Winkelmann, Florida Institute of Technology Edward P Zovinka, Saint Francis University

Previous Edition Accuracy reviewers

Margaret Asirvatham, University of Colorado, Boulder Rebecca Barlag, Ohio University

Angela Hoffman, University of Portland Louis Kirschenbaum, University of Rhode Island Richard Langley, Stephen F Austin State University Kathleen Thrush Shaginaw, Particular Solutions, Inc Sarah Siegel, Gonzaga University

Steven Socol, McHenry County College

Focus Group Participants

Yiyan Bai, Houston Community College Silas Blackstock, University of Alabama Jason Kautz, University of Nebraska (Lincoln) Michael Mueller, Rose-Hulman Institute of Technology Tom Pentecost, Grand Valley State University

Andrew Price, Temple University Cathrine Reck, Indiana University Sarah Siegel, Gonzaga University Shusien Wang-Batamo, Houston Community College Lin Zhu, Indiana University–Purdue University Indianapolis

Chemistry through Relevancy

Chemistry is relevant to every process occurring around us at every second Niva

Tro helps students understand this connection by weaving specific, vivid examples

throughout the text and media that tell the story of chemistry Every chapter begins

with a brief story showing how chemistry is relevant to all people, at every moment.

Visualizing Chemistry

Student-friendly, multipart images include macroscopic, molecular, and symbolic perspectives with the goal of connecting you to what you see and experience (macroscopic) with the molecules responsible for that world (molecular) and with the way chemists represent those molecules (symbolic) Illustrations include extensive labels and annotations

to highlight key elements and to help differentiate the most critical information (white box) to secondary information (beige box).

11 Liquids, Solids, and Intermolecular

forces that exist

among the particles

that compose matter.

429

WE LEARNED IN CHAPTER 1 THAT matter exists primarily in three states: solid, liquid, and gas In Chapter 5,

we examined the gas state In this chapter

we turn to the solid and liquid states, known collectively as the condensed states (or condensed phases) The solid and liquid states are more similar to each other than they are to the gas state In the gas state, the constituent particles—atoms or molecules—are separated by large distances and do not interact with each other very much In the condensed states, the constituent particles are close together and exert moderate to strong attractive forces on one another Whether a substance is a solid, liquid, or gas at room temperature depends on the magnitude of the attractive forces among the constituent particles In this chapter, we will see how the properties of a particular atom or molecule determine the magnitude of those attractive forces.

11.1 Water, No Gravity

In the space station there are no spills When an astronaut squeezes a full water bottle, the water squirts out like it does on Earth, but instead of falling to the floor and forming a the blob stops oscillating and forms a nearly perfect sphere Why?

It’s a wild dance floor there at the molecular level.

11.4 Intermolecular Forces in Action: Surface Tension, Viscosity, and Capillary Action 440

11.5 Vaporization and Vapor Pressure 442

11.6 Sublimation and Fusion 451

11.7 Heating Curve for Water 453

11.8 Phase Diagrams 454

11.9 Water: An Extraordinary Substance 456

11.10 Crystalline Solids: Unit Cells and Basic Structures 457

11.11 Crystalline Solids: The Fundamental Types 463

11.12 Crystalline Solids: Band Theory 467

Key Learning Objectives 471

160 Chapter 4 Chemical Quantities and Aqueous Reactions

However, redox reactions need not involve oxygen Consider, for example, the tion between sodium and chlorine to form sodium chloride (NaCl), depicted in FiguRe 4.17 ▲

fundamental definition of reduction is the gain of electrons.

The transfer of electrons, however, need not be a complete transfer (as occurs in the

formation of an ionic compound) for the reaction to qualify as oxidation–reduction For example, consider the reaction between hydrogen gas and chlorine gas:

H 2(g)+ Cl 2(g) S 2 HCl(g)

Even though hydrogen monochloride is a molecular compound with a covalent bond, and even though the hydrogen has not completely transferred its electron to chlorine during the reaction, you can see from the electron density diagrams ( FiguRe 4.18 ◀ ) that hydrogen

has lost some of its electron density—it has partially transferred its electron to chlorine

Therefore, in this reaction, hydrogen is oxidized and chlorine is reduced and the reaction

is a redox reaction.

NaCl(s)

Electron transfer

Electrons are transferred from sodium to chlorine, forming sodium chloride.

Sodium is oxidized and chlorine is reduced.

Oxidation–Reduction Reaction without Oxygen

▲ FiguRe 4.17 Oxidation–Reduction without Oxygen When sodium reacts with chlorine, electrons

are transferred from the sodium to the chlorine, resulting in the formation of sodium chloride In this redox reaction, sodium is oxidized and chlorine is reduced.

The reaction between sodium and oxygen

forms other oxides as well.

A helpful mnemonic is O I L R I G—Oxidation

Is Loss; Reduction Is Gain.

▲ FiguRe 4.18 Redox with Partial

Electron Transfer When hydrogen

bonds to chlorine, the electrons are

unevenly shared, resulting in an

increase of electron density (reduction)

for chlorine and a decrease in electron

density (oxidation) for hydrogen.

Interactive Problem-Solving Strategy

A unique yet consistent step-by-step format encourages logical thinking

throughout the problem-solving process rather than simply memorizing

formulas.

unique problem-solving strategies interactive, bringing

his award-winning teaching directly to all students using

his text In these digital, mobile versions, students are

instructed how to break down problems using Tro’s proven

Sort, Strategize, Solve, and Check technique.

Icons appear next to examples indicating a digital version is available in the etext and on mobile devices via a QR code located here, and on the back cover of your textbook.

4.2 Reaction Stoichiometry: How Much Carbon Dioxide? 129 Solution

We follow the conceptual plan to solve the problem, beginning with g C8H18 and

cancel-ing units to arrive at g CO2:

3.7 * 10 15 g C8H18*114.22 g C1 mol C8H18

8 H18* 16 mol CO2

2 mol C8H18*44.01 g CO1 mol CO2

2 = 1.1 * 10 16 g CO2The world’s petroleum combustion produces 1.1 * 10 16 g CO2 (1.1 * 10 13 kg) per year

In comparison, volcanoes produce about 2.0 * 10 11 kg CO 2 per year * In other words,

volcanoes emit only 2.0* 10 11 kg

1.1 * 10 13 kg * 100% = 1.8% as much CO 2 per year as leum combustion The argument that volcanoes emit more carbon dioxide than fossil fuel

petro-combustion is blatantly incorrect Examples 4.1 and 4.2 provide additional practice with

stoichiometric calculations.

The percentage of CO 2 emitted by volcanoes relative to all fossil fuels is even less than 2% because CO 2 is also emitted by the combustion of coal and natural gas.

* Gerlach, T M., Present-day CO 2 emissions from volcanoes; Eos, Transactions, American Geophysical Union,

Vol 72, No 23, June 4, 1991, pp 249 and 254–255

ExamPlE 4.1 Stoichiometry

During photosynthesis, plants convert carbon dioxide and water into glucose (C 6 H 12 O 6 ) according to the reaction:

6 CO 2(g)+ 6 H 2O(l) ˚˚˚˚sunlight "

6 O 2(g)+ C 6 H 12 O 6(aq)

Suppose a particular plant consumes 37.8 g CO 2 in one week Assuming that there is more than enough water present to

react with all of the CO 2 , what mass of glucose (in grams) can the plant synthesize from the CO 2 ?

SORT The problem gives the mass

of carbon dioxide and asks you to

find the mass of glucose that can

be produced.

GIVEN 37.8 g CO 2

FIND g C6 H 12 O 6

STRATEGIZE The conceptual plan

fol-lows the general pattern of mass

A S amount A (in moles) S

amount B (in moles) S mass B

From the chemical equation, you

can deduce the relationship

between moles of carbon dioxide

and moles of glucose Use the

molar masses to convert between

grams and moles.

molar mass C 6 H 12 O 6 = 180.16 g>mol

SOLVE Follow the conceptual plan

to solve the problem Begin with g

CO 2 and use the conversion factors

CHECK The units of the answer are correct The magnitude of the answer (25.8 g) is less than the initial mass of

CO 2 (37.8 g) This is reasonable because each carbon in CO 2 has two oxygen atoms associated with it, while in C 6 H 12 O 6

each carbon has only one oxygen atom associated with it and two hydrogen atoms, which are much lighter than oxygen

Therefore the mass of glucose produced should be less than the mass of carbon dioxide for this reaction.

FOR PRACTICE 4.1

Magnesium hydroxide, the active ingredient in milk of magnesia, neutralizes stomach acid, primarily HCl, according to the

reaction:

Mg(OH) 2(aq) + 2 HCl(aq) S 2 H2O(l)+ MgCl 2(aq)

What mass of HCl, in grams, is neutralized by a dose of milk of magnesia containing 3.26 g Mg (OH) 2 ?

M04_TRO1944_03_SE_C04_124-175v4.0.8.indd 129 17/10/14 11:12 AM

Magnesium hydroxide, the active ingredient in milk of magnesia, neutralizes stomach acid, primarily HCl, according to the

A Focus on Conceptual

Understanding

Key Concept Videos

with both 2D and 3D animations to create a dynamic on-screen viewing

and learning experience These short videos include narration and brief

live-action clips of author Niva Tro explaining the key concepts of each

chapter.

Each of the examples we examined in Section 10.2 has only bonding electron groups around the central atom What happens in molecules that have lone pairs around the cen-tral atom as well? These lone pairs also repel other electron groups, as we see in the examples that follow

Four Electron Groups with Lone Pairs

The Lewis structure of ammonia is shown here:

H

The central nitrogen atom has four electron groups (one lone pair and three bonding pairs) that repel one another If we do not distinguish between bonding electron groups and lone

pairs, we find that the electron geometry—the geometrical arrangement of the electron

groups—is still tetrahedral, as we expect for four electron groups However, the

molecu-lar geometry—the geometrical arrangement of the atoms—is trigonal pyramidal, as

shown here

KEY CONCEPT VIDEO

VSEPR Theory: The Effect

of Lone Pairs

Electron geometry:

tetrahedral

Molecular geometry:

trigonal pyramidal

NH

Lone pair

NH

Use the Lewis structure, or any one of the resonance structures, to determine the num- ber of electron groups around the central atom.

O

O –

The nitrogen atom has three electron groups.

Based on the number of electron groups, determine the geometry that minimizes the repulsions between the groups.

The electron geometry that minimizes the repulsions between three electron groups is trigonal planar

Because there are no lone pairs on the central atom, the molecular geometry is also trigonal planar.

Since the three bonds are equivalent, they each exert the same repulsion on the other two and the molecule has three equal bond angles of 120°.

FOR PRACTICE 10.1

Determine the molecular geometry of CCl4.

Continued from the previous page—

O

OO

Conceptual Connections

Conceptual Connections are strategically placed to reinforce

conceptual understanding of the most complex concepts

the ACS-exam and MCAT

style to help students

optimize the use of

quizzing to improve their

understanding and class

performance.

The Self Assessment

Quizzes are also

Molar Volume and Stoichiometry

In Section 5.5, we saw that, under standard temperature and pressure, 1 mol of an ideal gas occupies 22.4 L Consequently, if a reaction is occurring at or near standard tempera- ture and pressure, we can use 1 mol = 22.4 L as a conversion factor in stoichiometric calculations, as demonstrated in Example 5.13.

example 5.13 Using Molar Volume in Gas Stoichiometric Calculations

How many grams of water form when 1.24 L of H 2 gas at STP completely reacts with O 2 ?

2 H2(g)+ O 2(g) S 2 H 2O(g)

SORT You are given the volume of hydrogen gas

(a reactant) at STP and asked to determine the

mass of water that forms upon complete

reaction.

GIVEN 1.24 L H 2

FIND g H2O

STRATEGIZE Since the reaction occurs under

standard temperature and pressure, you can

convert directly from the volume (in L) of

hydro-gen gas to the amount in moles Then use the

stoichiometric relationship from the balanced

equation to find the number of moles of water

that forms Finally, use the molar mass of water

to obtain the mass of water.

CONCEPTUAL PLAN

g H 2 O mol H 2 O

CHECK The units of the answer are correct The magnitude of the answer (0.998 g) is about 1>18 of the molar mass of water,

roughly equivalent to the approximately 1 >22 of a mole of hydrogen gas given, as expected for a 1:1 stoichiometric

relation-ship between number of moles of hydrogen and number of moles of water.

FOR PRACTICE 5.13

How many liters of oxygen (at STP) are required to form 10.5 g of H2O?

2 H 2(g)+ O 2(g) S 2 H 2O(g)

CONCEPTUAL

CONNECTION 5.5 PRESSURE AND NUMBER OF MOLES

Nitrogen and hydrogen react to form ammonia according to the equation:

N2(g)+ 3 H 2(g) L 2 NH 3(g)

Consider the representations shown here of the initial mixture of reactants and the resulting mixture after the reaction has been allowed to react for some time.

If the volume is kept constant, and nothing is added to the reaction mixture, what happens to the total pressure during the course of the reaction?

(a) The pressure increases.

(b) The pressure decreases.

(c) The pressure does not change.

M05_TRO1944_03_SE_C05_176-219v4.0.3.indd 200 30/07/14 1:11 PM

724 Chapter 17 Free Energy and Thermodynamics

ExamplE 17.10 The Equilibrium Constant and 𝚫𝚫G∙rxn

Use tabulated free energies of formation to calculate the equilibrium constant for the following reaction at 298 K:

N 2 O 4(g)L 2 NO 2(g)

SOLuTiON

Begin by looking up (in Appendix IIB) the standard free energies of formation for each reactant and product.

reactant or product 𝚫𝚫G∙f (kJ>mol)

Calculate K from ΔG°rxn by solving

Equation 17.15 for K and substituting the

values of ΔG° rxn and temperature.

ΔG°rxn=-RT ln K

ln K = - ΔG°rxn

RT

= -2.8 * 10 3 J >mol 8.314 Jmol # K (298 K) = -1.13

The reaction A(g) L B(g) has an equilibrium constant that is less than one What

can you conclude about ΔG° rxn for the reaction?

(a) ΔG°rxn = 0 (b) ΔG°rxn 6 0 (c) ΔG°rxn 7 0

Self-assessment Quiz

Q1 Which reaction is most likely to have a positive ΔSsys ?

a SiO2(s) + 3 C(s) S SiC(s) + 2 CO(g)

b 6 CO2(g) + 6 H2O(g) S C6 H 12 O 6(s) + 6 O2(g)

c CO(g) + Cl 2(g) S COCl2(g)

d 3 NO2(g) + H 2O(l) S 2 HNO 3(l) + NO(g)

Q2 Consider the signs for ΔHrxn and ΔS rxn for several different reactions In which case is the reaction spontaneous at all temperatures?

a.ΔHrxn6 0; ΔSrxn6 0 b.ΔHrxn7 0; ΔSrxn 7 0

c.ΔHrxn6 0; ΔSrxn 7 0 d ΔHrxn7 0; ΔSrxn 6 0

Q3 Arrange the gases—F2 , Ar, and CH 3 F—in order of

increas-ing standard entropy (S°) at 298 K.

a F2 6 Ar 6 CH 3F b CH3 F 6 F 2 6 Ar

c CH3 F 6 Ar 6 F 2 d Ar 6 F 2 6 CH 3 F

Q4 For a certain reaction ΔHrxn = 54.2 kJ Calculate the change

in entropy for the surroundings (ΔS surr ) for the reaction at 25.0 °C (Assume constant pressure and temperature.)

Q1 A chemist mixes sodium with water and witnesses a violent

reaction between the metal and water This is best classified as:

a an observation b a law

c a hypothesis d a theory Q2 This image represents a particulate view of a sample of mat-

ter Classify the sample according to its composition.

a The sample is a pure element.

b The sample is a homogeneous mixture.

c The sample is a compound.

d The sample is a heterogeneous mixture.

Q3 Which change is a physical change?

a wood burning b iron rusting

c dynamite exploding d gasoline evaporating Q4 Which property of rubbing alcohol is a chemical property?

a its density (0.786 g>cm 3 )

b its flammability

c its boiling point (82.5 °C)

d its melting point (-89 °C)

Q5 Convert 85.0 °F to K.

a 181.1 K b 358 K c 29.4 K d 302.6 K Q6 Express the quantity 33.2* 10 -4 m in mm.

figures.

(8.01 - 7.50)>3.002

a 0.1698867 b 0.17 c 0.170 d 0.1700 Q10 Convert 1285 cm2 to m 2

a 1.285* 10 7 m 2

b 12.85 m2

c 0.1285 m2

d 1.285* 10 5 m 2

Q11 The first diagram shown here depicts a compound in its

liq-uid state Which of the diagrams that follow best depicts the compound after it has evaporated into a gas?

Q12 Three samples, each of a different substance, are weighed

and their volume is measured The results are tabulated here

List the substances in order of decreasing density.

Substance I 10.0 g 10.0 mL Substance II 10.0 kg 12.0 L Substance III 12.0 mg 10.0 mL

a III 7 II 7 I b I7 II 7 III

c III 7 I 7 II d II7 I 7 III

Q13 A solid metal sphere has a radius of 3.53 cm and a mass of

1.796 kg What is the density of the metal in g >cm 3 ? (The

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1 Matter, Measurement, and

(the linked red and

black spheres) as well

as oxygen.

WHAT DO YOU THINK Is THe mOsT

important idea in all of human knowledge? There are, of course, many possible answers to this question—some practical, some philosophical, and some scientific If we limit ourselves only to

scientific answers, mine would be this: The

properties of matter are determined by the properties of molecules and atoms Atoms

and molecules determine how matter behaves—if they were different, matter would be different The properties of water molecules, for example, determine how water behaves; the properties of sugar molecules determine how sugar behaves;

and the molecules that compose our bodies determine how our bodies behave The understanding of matter at the molecular level gives us unprecedented control over that matter For example, our understanding of the details of the molecules that compose living organisms has revolutionized biology over the last 50 years

The most incomprehensible thing about the universe is that it is

comprehensible.

—Albert Einstein (1879–1955)

Changes and Physical and

of Physical and Chemical

Key Learning Objectives 34

The air over most U.S cities, including my own, contains at least some pollution A significant component of that pollution is carbon monoxide, a colorless gas emitted in the

exhaust of cars and trucks Carbon monoxide gas is composed of carbon monoxide molecules, each of which contains a carbon atom and an oxygen atom held together by a

chemical bond Atoms are the submicroscopic particles that constitute the fundamental

building blocks of ordinary matter However, free atoms are rare in nature; instead, they

bind together in specific geometric arrangements to form molecules.

4 Chapter 1 Matter, Measurement, and Problem Solving

The properties of the substances around us depend on the atoms and molecules that

compose them, so the properties of carbon monoxide gas depend on the properties of carbon monoxide molecules Carbon monoxide molecules happen to be just the right size

and shape, and happen to have just the right chemical properties, to fit neatly into cavities within hemoglobin—the oxygen-carrying molecule in blood—that normally carry oxy-gen molecules (Figure 1.1 ▲ ) Consequently, carbon monoxide diminishes the oxygen-carrying capacity of blood Breathing air containing too much carbon monoxide (greater than 0.04% by volume) can lead to unconsciousness and even death because not enough oxygen reaches the brain Carbon monoxide deaths have occurred, for example, as a result of running an automobile in a closed garage or using a propane burner in an enclosed space for too long In smaller amounts, carbon monoxide causes the heart and lungs to work harder and can result in headache, dizziness, weakness, and confusion.Cars and trucks emit a closely related molecule, called carbon dioxide, in far greater quantities than carbon monoxide The only difference between carbon dioxide and carbon monoxide is that carbon dioxide molecules contain two oxygen atoms instead of just one This extra oxygen atom dramatically affects the properties of the gas We breathe much more carbon dioxide—which composes 0.04% of air and is a product of our own respira-tion as well—than carbon monoxide, yet it does not kill us Why? Because the presence of the second oxygen atom prevents carbon dioxide from binding to the oxygen-carrying site

in hemoglobin, making it far less toxic Although high levels of carbon dioxide (greater than 10% of air) can be toxic for other reasons, lower levels can enter the bloodstream with

no adverse effects Such is the molecular world Any differences between molecules—such

as the presence of the extra oxygen atom in carbon dioxide compared to carbon monoxide—results in differences between the substances that the molecules compose

As another example, consider two other closely related molecules, water and hydrogen peroxide:

In the study of chemistry, atoms are often

portrayed as colored spheres, with each

color representing a different kind of atom

For example, a black sphere represents a

carbon atom, a red sphere represents an

oxygen atom, and a white sphere represents

a hydrogen atom For a complete color code

of atoms, see Appendix IIA.

Oxygen atom

Carbon

atom

Carbon monoxide molecule

Oxygen atom

Oxygen

atom

Carbon

atom

Carbon dioxide molecule

Hemoglobin, the oxygen-carrying molecule in red blood cells

Carbon monoxide can bind

to the site on hemoglobin that normally carries oxygen.

▲  Figure 1.1 Binding of Oxygen and Carbon Monoxide to Hemoglobin Hemoglobin, a large protein

molecule, is the oxygen carrier in red blood cells Each subunit of the hemoglobin molecule contains

an iron atom to which oxygen binds Carbon monoxide molecules can take the place of oxygen, thus reducing the amount of oxygen reaching the body’s tissues.

Hydrogen atoms

Oxygen atom

Hydrogen atoms

Oxygen atoms

KEY CONCEPT VIDEO

Atoms and Molecules

1.2 The Scientific Approach to Knowledge 5

A water molecule is composed of one oxygen atom and two hydrogen atoms A hydrogen

peroxide molecule is composed of two oxygen atoms and two hydrogen atoms This

seem-ingly small molecular difference results in a huge difference in the properties of water and

hydrogen peroxide Water is the familiar and stable liquid we all drink and bathe in Hydrogen

peroxide, in contrast, is an unstable liquid that, in its pure form, burns the skin on contact and

is used in rocket fuel When you pour water onto your hair, your hair simply becomes wet

However, if you put hydrogen peroxide in your hair—which you may have done if you have

ever bleached your hair—a chemical reaction occurs that turns your hair blonde

The details of how specific atoms bond to form a molecule—in a straight line, at a

particular angle, in a ring, or in some other pattern—as well as the type of atoms in the

molecule, determine everything about the substance that the molecule composes If we

want to understand the substances around us, we must understand the atoms and

mole-cules that compose them—this is the central goal of chemistry A good simple definition

of chemistry is, therefore,

Chemistry—the science that seeks to understand the behavior of matter

by studying the behavior of atoms and molecules.

Scientific knowledge is empirical—it is based on observation and experiment Scientists

observe and perform experiments on the physical world to learn about it Some

observa-tions and experiments are qualitative (noting or describing how a process happens), but

many are quantitative (measuring or quantifying something about the process) For

example, Antoine Lavoisier (1743–1794), a French chemist who studied combustion,

made careful measurements of the mass of objects before and after burning them in

closed containers He noticed that there was no change in the total mass of material

within the container during combustion Lavoisier made an important observation about

the physical world

Observations often lead a scientist to formulate a hypothesis, a tentative

interpreta-tion or explanainterpreta-tion of the observainterpreta-tions For example, Lavoisier explained his

observa-tions on combustion by hypothesizing that when a substance burns, it combines with a

component of air A good hypothesis is falsifiable, which means that it makes predictions

that can be confirmed or refuted by further observations Hypotheses are tested by

exper-iments, highly controlled procedures designed to generate observations that can confirm

or refute a hypothesis The results of an experiment may support a hypothesis or prove it

wrong If it is proven wrong, the hypothesis must be modified or discarded

In some cases, a series of similar observations can lead to the development of a

scientific law, a brief statement that summarizes past observations and predicts future

ones For example, Lavoisier summarized his observations on combustion with the law

of conservation of mass, which states, “In a chemical reaction, matter is neither created

nor destroyed.” This statement summarizes Lavoisier’s observations on chemical

reac-tions and predicts the outcome of future observareac-tions on reacreac-tions Laws, like

hypothe-ses, are also subject to experiments, which can add support to them or prove them wrong

Scientific laws are not laws in the same sense as civil or governmental laws Nature

does not follow laws in the way that we obey the laws against speeding or running a red

light Rather, scientific laws describe how nature behaves—they are generalizations

about what nature does For that reason, some people find it more appropriate to refer to

them as principles rather than laws.

One or more well-established hypotheses may form the basis for a scientific theory

A scientific theory is a model for the way nature is and tries to explain not merely what

nature does, but why As such, well-established theories are the pinnacle of scientific

knowledge, often predicting behavior far beyond the observations or laws from which

they were developed A good example of a theory is the atomic theory proposed by

English chemist John Dalton (1766–1844) Dalton explained the law of conservation of

mass, as well as other laws and observations of the time, by proposing that matter is

com-posed of small, indestructible particles called atoms Since these particles merely

rear-range in chemical changes (and do not form or vanish), the total amount of mass remains

The hydrogen peroxide used as an antiseptic

or bleaching agent is considerably diluted.

Antoine Lavoisier Lavoisier, who also made significant contributions to agriculture, industry, education, and government administration, was executed during the French Revolution.

In Dalton’s time, atoms were thought to be indestructible Today, because of nuclear reactions, we know that atoms can be broken apart into their smaller components.

6 Chapter 1 Matter, Measurement, and Problem Solving

the same Dalton’s theory is a model for the physical world—it gives us insight into how

nature works, and therefore explains our laws and observations.

Finally, the scientific approach returns to observation to test theories For example, scientists can test the atomic theory by trying to isolate single atoms, or by trying to image them (both of which, by the way, have already been accomplished) Theories are validated

by experiments; however, theories can never be conclusively proven because some new observation or experiment always has the potential to reveal a flaw Notice that the scien-tific approach to knowledge begins with observation and ends with observation, because an experiment is simply a highly controlled procedure for generating critical observations designed to test a theory or hypothesis Each new set of observations has the potential to refine the original model Figure 1.2 ▲ is one way to map the scientific approach to knowl-edge Scientific laws, hypotheses, and theories are all subject to continued experimentation

If a law, hypothesis, or theory is proved wrong by an experiment, it must be revised and tested with new experiments Over time, poor theories and laws are eliminated or corrected and good theories and laws—those consistent with experimental results—remain

Established theories with strong experimental support are the most powerful pieces

of scientific knowledge You may have heard the phrase, “That is just a theory,” as if ries are easily dismissible Such a statement reveals a deep misunderstanding of the nature of a scientific theory Well-established theories are as close to truth as we get in science The idea that all matter is made of atoms is “just a theory,” but it has over 200 years of experimental evidence to support it It is a powerful piece of scientific knowl-edge on which many other scientific ideas have been built

theo-One last word about the scientific approach to knowledge: Some people wrongly imagine science to be a strict set of rules and procedures that automatically leads to inar-guable, objective facts This is not the case Even the diagram of the scientific approach

to knowledge in Figure 1.2 is only an idealization of real science, useful to help us see key distinctions Doing real science requires hard work, care, creativity, and even a bit of luck Scientific theories do not just fall out of data—they are crafted by men and women

of great genius and creativity A great theory is not unlike a master painting, and many see a similar kind of beauty in both

Test Confirm

(or revise law)

Confirm (or revise hypothesis)

Confirm (or revise theory)

Test Test

Hypothesis

Law

Theory

The Scientific Approach to Knowledge

▲  Figure 1.2 The Scientific Approach

COnCEPTUAL

COnnECTiOn 1.1 LAwS And THEORiES

Which statement best explains the difference between a law and a theory?

(a) A law is truth, whereas a theory is mere speculation.

(b) A law summarizes a series of related observations, whereas a theory gives the

underlying reasons for them

(c) A theory describes what nature does, whereas a law describes why nature does it.

You can find the answers to conceptual

connection questions at the end of each

chapter.

1.3 The Classification of Matter 7

Matter is anything that occupies space and has mass This book, your desk, your chair,

and even your body are all composed of matter Less obviously, the air around you is also

matter—it too occupies space and has mass We often call a specific instance of matter—

such as air, water, or sand—a substance We classify matter according to its state—solid,

liquid, or gas—and according to its composition

The States of Matter: Solid, Liquid, and Gas

Matter exists in three different states: solid, liquid, and gas In solid matter, atoms

or molecules pack closely to each other in fixed locations Although the atoms and

molecules in a solid vibrate, they do not move around or past each other Consequently,

a solid has a fixed volume and rigid shape Ice, aluminum, and diamond are examples

of solids Solid matter may be crystalline, in which case its atoms or molecules are

arranged in patterns with long-range, repeating order (Figure 1.3 ▶), or it may be

amorphous, in which case its atoms or molecules do not have any long-range order

Examples of crystalline solids include table salt and diamond; the well-ordered

geo-metric shapes of salt and diamond crystals reflect the well-ordered geogeo-metric

arrangement of their atoms Examples of amorphous solids include glass and most

plastics

In liquid matter, atoms or molecules pack about as closely as they do in solid matter,

but are free to move relative to each other, giving liquids a fixed volume but not a fixed

shape Liquids assume the shape of their container Water, alcohol, and gasoline are

substances that are liquids at room temperature

Crystalline:

Regular 3-dimensional pattern

Diamond

C (s, diamond)

▲  Figure 1.3 Crystalline Solids

Diamond is a crystalline solid composed of carbon atoms arranged in

a regular, repeating pattern.

The state of matter changes from solid to liquid to gas with increasing temperature.

Solid matter Liquid matter Gaseous matter

although the atoms or molecules are closely packed, they can move past one another,

allowing the liquid to flow and assume the shape of its container In a gas, the atoms or

molecules are widely spaced, making gases compressible as well as fluid.

8 Chapter 1 Matter, Measurement, and Problem Solving

Variable composition?

Mixture Pure Substances

Compound Element

Yes

Yes

Matter

In gaseous matter, atoms or molecules have a lot of space

between them and are free to move relative to one another, making

gases compressible (Figure 1.4 ◀) When you squeeze a balloon or sit down on an air mattress, you force the atoms and molecules into a smaller space, so that they are closer together Gases always assume

the shape and volume of their container Substances that are gases at

room temperature include helium, nitrogen (the main component of air), and carbon dioxide

Classifying Matter According to its Composition: Elements, Compounds, and Mixtures

In addition to classifying matter according to its state, we can

clas-sify it according to its composition, that is, the kinds and amounts

of substances that compose it The following chart classifies matter according to its composition:

Solid–not compressible Gas–compressible

The first division in the classification of matter depends on whether or not its position can vary from one sample to another For example, the composition of distilled

com-(or pure) water never varies—it is always 100% water and is therefore a pure substance,

a substance composed of only a single type of atom or molecule In contrast, the composition of sweetened tea can vary considerably from one sample to another, depend-ing, for instance, on the strength of the tea or how much sugar has been added Sweetened

tea is an example of a mixture, a substance composed of two or more different types of

atoms or molecules that can be combined in continuously variable proportions

▲  Figure 1.4 The Compressibility of Gases Gases can be

compressed—squeezed into a smaller volume—because there is

so much empty space between atoms or molecules in the

gaseous state.

1.4 Physical and Chemical Changes and Physical and Chemical Properties 9

All known elements are listed in the periodic table in the inside front cover of this book.

We can categorize pure substances into two types—elements and

compounds—depend-ing on whether or not they can be broken down into simpler substances The helium in a

blimp or party balloon is an example of an element, a substance that cannot be chemically

broken down into simpler substances Water is an example of a compound, a substance

com-posed of two or more elements (hydrogen and oxygen) in fixed, definite proportions On

Earth, compounds are more common than pure elements because most elements combine

with other elements to form compounds

We can also categorize mixtures into two types—heterogeneous and homogeneous—

depending on how uniformly the substances within them mix Wet sand is an example of a

heterogeneous mixture, one in which the composition varies from one region to another

Sweetened tea is an example of a homogeneous mixture, one with the same composition

throughout Homogeneous mixtures have uniform compositions because the atoms or

mol-ecules that compose them mix uniformly Heterogeneous mixtures are made up of distinct

regions because the atoms or molecules that compose them separate Here again we see

that the properties of matter are determined by the atoms or molecules that compose it

COnCEPTUAL COnnECTiOn 1.2

PURE SUBSTAnCES And MixTURES

Let a small circle represent an atom of one type of element and a small square represent

an atom of a second type of element Make a drawing of: (a) a pure substance composed

of the two elements (in a one-to-one ratio); (b) a homogeneous mixture composed of

the two elements; and (c) a heterogeneous mixture composed of the two elements.

and Chemical Properties

Every day we witness changes in matter: ice melts, iron rusts, gasoline burns, fruit ripens,

and water evaporates What happens to the molecules that compose these samples of

mat-ter during such changes? The answer depends on the type of change Changes that almat-ter

only state or appearance, but not composition, are physical changes The atoms or

mole-cules that compose a substance do not change their identity during a physical change For

example, when water boils, it changes its state from a liquid to a gas, but the gas remains

composed of water molecules, which means that this is a physical change (Figure 1.5 ▼ )

H 2O(g)

H 2O(l)

Water molecules change from liquid

to gaseous state: physical change.

◀  Figure 1.5 Boiling, a Physical Change When water boils, it turns

into a gas but does not alter its chemical identity—the water molecules are the same in both the liquid and gaseous states Boiling is a physical change, and the boiling point

of water is a physical property.

You can find the answers to conceptual connection questions at the end of each chapter.

10 Chapter 1 Matter, Measurement, and Problem Solving

A physical change results in a different form

of the same substance, while a chemical

change results in a completely different

substance.

Iron atoms

Iron oxide

(rust)

▲  Figure 1.6 Rusting, a Chemical

Change When iron rusts, the iron

atoms combine with oxygen atoms to

form a different chemical substance, a

compound called iron oxide Rusting

is a chemical change, and the tendency

of iron to rust is a chemical property.

In contrast, changes that alter the composition of matter are chemical changes

During a chemical change, atoms rearrange, transforming the original substances into different substances For example, the rusting of iron is a chemical change (Figure 1.6 ◀) The atoms that compose iron (iron atoms) combine with oxygen molecules from air to form iron oxide, the orange substance we normally call rust Figure 1.7 ▶ illustrates some other examples of physical and chemical changes

Physical and chemical changes are manifestations of physical and chemical

proper-ties A physical property is one that a substance displays without changing its tion, whereas a chemical property is one that a substance displays only by changing its

composi-composition via a chemical change For example, the smell of gasoline is a physical

property—gasoline does not change its composition when it exhibits its odor The mability of gasoline, however, is a chemical property—gasoline does change its composi-tion when it burns, turning into completely new substances (primarily carbon dioxide and water) Physical properties include odor, taste, color, appearance, melting point, boiling point, and density Chemical properties include corrosiveness, flammability, acidity, and toxicity

flam-The differences between physical and chemical changes are not always apparent Only chemical examination can confirm whether a particular change is physical or chem-ical In many cases, however, we can identify chemical and physical changes based on what we know about the changes Changes in the state of matter, such as melting or boil-ing, or changes in the physical condition of matter, such as those that result from cutting

or crushing, are typically physical changes Changes involving chemical reactions—often evidenced by heat exchange or color changes—are chemical changes

You can find the answers to For Practice and

For More Practice problems in Appendix IV.

ExamPlE 1.1 Physical and Chemical Changes and Properties

Is each change physical or chemical? Which kind of property (chemical or physical) is demonstrated in each case?

(a) the evaporation of rubbing alcohol (b) the burning of lamp oil

(c) the bleaching of hair with hydrogen peroxide (d) the forming of frost on a cold night

SOLUTiOn

(a) When rubbing alcohol evaporates, it changes from liquid to gas, but it remains alcohol—this is a physical change The volatility (ability to evaporate easily) of alcohol is a physical property.

(b) Lamp oil burns because it reacts with oxygen in air to form carbon dioxide and water—this is a chemical change The flammability of lamp oil is a chemical property.

(c) Applying hydrogen peroxide to hair changes pigment molecules in hair that give it color—this is a chemical change The susceptibility of hair to bleaching is a chemical property.

(d) Frost forms on a cold night because water vapor in air changes its state to form solid ice—this is a physical change The temperature at which water freezes is a physical property.

FOR PRACTiCE 1.1

Is each change physical or chemical? Which kind of property (chemical or physical) is demonstrated in each case?

(a) A copper wire is hammered flat.

(b) A nickel dissolves in acid to form a blue-green solution.

(c) Dry ice sublimes (changes into a gas) without melting.

(d) A match ignites when struck on a flint.

1.4 Physical and Chemical Changes and Physical and Chemical Properties 11

C 12 H 22 O 11(s)

Solid sugar

C 12 H 22 O 11(aq)

Dissolved sugar molecules

Propane gas burning:

Physical Change and Chemical Change

CHEMiCAL And PHySiCAL CHAnGES

The diagram in the right margin represents liquid water molecules in a pan Which

of the diagrams shown below best represents the water molecules after they have

been vaporized by the boiling of liquid water?