Main Basic Concepts of Chemistry, Eighth Edition
Basic Concepts of Chemistry, Eighth EditionLeo J. Malone, Theodore Dolter
Engineers who need to have a better understanding of chemistry will benefit from this accessible book. It places a stronger emphasis on outcomes assessment, which is the driving force for many of the new features. Each section focuses on the development and assessment of one or two specific objectives. Within each section, a specific objective is included, an anticipatory set to orient the reader, content discussion from established authors, and guided practice problems for relevant objectives. These features are followed by a set of independent practice problems. The expanded Making it Real feature showcases topics of current interest relating to the subject at hand such as chemical forensics and more medical related topics. Numerous worked examples in the text now include Analysis and Synthesis sections, which allow engineers to explore concepts in greater depth, and discuss outside relevance.
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It’s all here: www.wileyplus.com TECHNICAL SUPPORT: A fully searchable knowledge base of FAQs and help documentation, available 24/7 Live chat with a trained member of our support staff during business hours A form to ﬁll out and submit online to ask any question and get a quick response Instructor-only phone line during business hours: 1.877.586.0192 FACULTY-LED TRAINING THROUGH THE WILEY FACULTY NETWORK: Register online: www.wherefacultyconnect.com Connect with your colleagues in a complimentary virtual seminar, with a personal mentor in your ﬁeld, or at a live workshop to share best practices for teaching with technology. 1ST DAY OF CLASS…AND BEYOND! Resources You & Your Students Need to Get Started & Use WileyPLUS from the first day forward. 2-Minute Tutorials on how to set up & maintain your WileyPLUS course User guides, links to technical support & training options WileyPLUS for Dummies: Instructors’ quick reference guide to using WileyPLUS Student tutorials & instruction on how to register, buy, and use WileyPLUS YOUR WileyPLUS ACCOUNT MANAGER: Your personal WileyPLUS connection for any assistance you need! SET UP YOUR WileyPLUS COURSE IN MINUTES! Selected WileyPLUS courses with QuickStart contain pre-loaded assignments & presentations created by subject matter experts who are also experienced WileyPLUS users. Interested? See and try WileyPLUS in action! Details and Demo: www.wileyplus.com MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page v BASIC CONCE PTS OF CH E M ISTRY 8th EDITION L E O J . M A LO N E St. Louis University T H E O D O R E O . D O LT E R Southwestern Illinois College John Wiley & Sons, Inc. MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page vi VICE PRESIDENT AND EXECUTIVE PUBLISHER ASSOCIATE PUBLISHER ACQUISITIONS EDITOR PROJECT EDITOR PRODUCTION SERVICES MANAGER PRODUCTION EDITOR EXECUTIVE MARKETING MANAGER CREATIVE DIRECTOR SENIOR PHOTO EDITOR SENIOR DESIGNER INTERIOR DESIGN COVER DESIGN EDITORIAL PROGRAM ASSISTANT SENIOR MEDIA EDITOR PRODUCTION SERVICES COVER IMAGES Kaye Pace Petra Recter Nicholas Ferrari Joan Kalkut Dorothy Sinclair Janet Foxman Amanda Wainer Harry Nolan Lisa Gee Kevin Murphy Brian Salisbury Hope Miller Catherine Donovan Thomas Kulesa Suzanne Ingrao/Ingrao Associates ©Corbis/Media Bakery This volume contains selected illustrations from the following texts, reprinted by permission from John Wiley and Sons, Inc. • Brady, James E.; Senese, Fred, Chemistry: Matter and Its Changes, Fourth Edition, ©2004. • Brady, James E.; Senese, Fred, Chemistry: Matter and Its Changes, Fifth Edition, ©2009. • Hein, Morris; Arena, Susan, Foundations of College Chemistry, Twelfth Edition, ©2007. • Murck, Barbara; Skinner, Brian, MacKenzie, Visualizing Geology, First Edition, ©2008. • Olmsted III, John; Williams, Gregory M., Chemistry, Fourth Edition, ©2006. • Pratt, Charlotte W.; Cornely, Kathleen, Essential Biochemistry, First Edition, ©2004. • Raymond, Kenneth, General, Organic, and Biological Chemistry: An Integrated Approach, Second Edition, ©2008. 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To order books or for customer service, please call 1-800-CALL WILEY (225-5945). Library of Congress Cataloging-in-Publication Data Malone Leo J., 1938Basic concepts of chemistry / Leo J. Malone, Theodore O. Dolter. – 8th ed. p. cm. ISBN 978-0-471-74154-1 (cloth) 1. Chemistry–Textbooks. I. Dolter, Theodore O., 1965- II. Title. QD31.3.M344 2010 540–dc22 2008036140 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page vii A B O U T T H E A U T H O R S LEO J. MALON E Leo Malone is a native of Kansas where he received his B.S. in Chemistry from Wichita State University in 1960 and M.S. in Chemistry in 1962. At WSU he worked under the direction of Dr. Robert Christian. He moved on to the University of Michigan where he received his Ph.D. in 1964 under the direction of Dr. Robert Parry. Dr. Malone began his teaching career at Saint Louis University in 1965 where he remained until his retirement as Professor Emeritus in 2005. Although his early research at SLU involved boron hydride chemistry, he eventually concentrated his efforts on the teaching of basic chemistry and in the field of chemical education. T H E O D O R E ( T E D ) O . D O LT E R Ted Dolter received his B.S. in Chemistry from St. Louis University in 1987, where he was a student of Dr. Malone’s. He went on to the University of Illinois where he received a Masters of Chemical Education in 1990. He concurrently earned a secondary teaching certificate, and it was there that he received most of his training in modern educational theory. After six years of teaching high school chemistry and evening courses at Southwestern Illinois College, he joined the faculty at SWIC full time. In 2004, he was elected to the Department Chair position, where he currently serves and is involved in the department’s outcomes assessment initiative. Professor Dolter’s background in educational training and his knowledge of the needs of the growing numbers of community college students compliment Dr. Malone’s years of traditional university educational experience. Together, they have produced a text that remains flexible and applicable to the rapidly changing face of today’s post-secondary student population. vii MALO_FM_i-1_hr2.qxd 13-10-2008 B R I E F PROLOGUE CHAPTER 1 CHAPTER 2 CHAPTER 3 CHAPTER 4 CHAPTER 5 CHAPTER 6 CHAPTER 7 CHAPTER 8 CHAPTER 9 11:52 Page viii C O N T E N T S Introduction to the Study of Chemistry 2 Measurements in Chemistry 14 Elements and Compounds 50 The Properties of Matter and Energy 78 The Periodic Table and Chemical Nomenclature 108 Chemical Reactions 136 Quantities in Chemistry 168 Quantitative Relationships in Chemical Reactions 196 Modern Atomic Theory 220 The Chemical Bond 252 The Gaseous State 292 CHAPTER 11 The Solid and Liquid States 330 CHAPTER 12 Aqueous Solutions 362 CHAPTER 13 Acids, Bases, and Salts 396 CHAPTER 14 Oxidation–Reduction Reactions 436 CHAPTER 15 Reaction Rates and Equilibrium 470 CHAPTER 16 Nuclear Chemistry 510 CHAPTER 17 Organic Chemistry (WEB) w-2 CHAPTER 18 Biochemistry (WEB) w-42 Foreword to the Appendices A-1 APPENDIX A Basic Mathematics A-1 APPENDIX B Basic Algebra A-10 APPENDIX C Scientific Notation A-19 APPENDIX D Graphs A-27 APPENDIX E Calculators A-31 APPENDIX F Glossary A-36 APPENDIX G Answers to Problems A-45 CHAPTER 10 viii MALO_FM_i-1_hr2.qxd 13-10-2008 11:51 Page ix C O N T E N T S PROLOGUE Science and the Magnificent Human Mind A B C 2 The Origin of Matter 4 The Mystery of Fire 9 The Scientific Method 10 CHAPTER 1 Measurements in Chemistry PA R T A 14 1-1 The Numerical Value of a Measurement 16 1-2 Significant Figures and Mathematical Operations 19 1-3 Expressing Large and Small Numbers: Scientific Notation MAKING IT REAL: Ted Williams and Significant Figures PA R T A S U M M A R Y PA R T B 16 THE NUMBERS USED IN CHEMISTRY 22 22 25 THE MEASUREMENTS USED IN CHEMISTRY 26 1-4 Measurement of Mass, Length, and Volume 26 1-5 Conversion of Units by the Factor-Label Method 30 MAKING IT REAL: Worlds from the Small to the Distant— Picometers to Terameters 31 1-6 Measurement of Temperature 38 PA R T B S U M M A R Y 41 Chapter Summary 41 Chapter Problems 43 CHAPTER 2 Elements and Compounds PA R T A 50 THE ELEMENTS AND THEIR COMPOSITION 2-1 The Elements 52 52 MAKING IT REAL: Iridium, the Missing Dinosaurs, and the Scientific Method 55 2-2 The Composition of Elements: Atomic Theory 56 2-3 Composition of the Atom 58 2-4 Atomic Number, Mass Number, and Atomic Mass 60 MAKING IT REAL: Isotopes and the History of Earth’s Weather PA R T A S U M M A R Y 62 64 ix MALO_FM_i-1_hr1.qxd x 7-10-2008 17:03 Page x CONTENTS PA R T B COMPOUNDS AND THEIR COMPOSITION 64 2-5 Molecular Compounds 2-6 Ionic Compounds 67 MAKING IT REAL: 64 Ionic Compounds and Essential Elements PA R T B S U M M A R Y Chapter Summary Chapter Problems 71 71 72 74 CHAPTER 3 The Properties of Matter and Energy PA R T A T H E P R O P E R T I E S O F M AT T E R 3-1 The Physical and Chemical Properties of Matter 3-2 Density—A Physical Property 84 MAKING IT REAL: PA R T A S U M M A R Y B 80 80 Identifying a Glass Shard from a Crime Scene by Density 3-3 The Properties of Mixtures PA R T 78 89 93 TH E PR OPE RTI ES OF E N E R GY 3-4 The Forms and Types of Energy 94 3-5 Energy Measurement and Specific Heat 94 96 MAKING IT REAL: Body Solutions—Lose Weight (actually money) While You Sleep 99 MAKING IT REAL: Dark Matter and Energy PA R T B S U M M A R Y Chapter Summary Chapter Problems 88 100 101 102 104 CHAPTER 4 The Periodic Table and Chemical Nomenclature PA R T A R E L AT I O N S H I P S A M O N G T H E E L E M E N T S A N D T H E P E R I O D I C TA B L E 110 4-1 The Origin of the Periodic Table 4-2 Using the Periodic Table 112 MAKING IT REAL: B 110 The Discovery of a Group VIIA Element, Iodine PA R T A S U M M A R Y PA R T 108 114 116 THE FORMULAS AND NAMES OF COMPOUNDS 116 4-3 Naming and Writing Formulas of Metal-Nonmetal Binary Compounds 117 4-4 Naming and Writing Formulas of Compounds with Polyatomic Ions 121 M A K I N G I T R E A L : Ionic Compounds in the Treatment of Disease 124 4-5 Naming Nonmetal-Nonmetal Binary Compounds 125 4-6 Naming Acids 127 PA R T B S U M M A R Y 129 Chapter Summary 130 Chapter Problems 132 MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xi CONTENTS CHAPTER 5 Chemical Reactions PA R T A 136 T H E R E P R E S E N TAT I O N O F C H E M I C A L CHANGES AND THREE TYPES OF CHANGES 138 5-1 Chemical Equations 138 5-2 Combustion, Combination, and Decomposition Reactions MAKING IT REAL: PA R T A S U M M A R Y PA R T B 143 Life Where the Sun Doesn’t Shine—Chemosynthesis I O N S I N W AT E R A N D H O W T H E Y R E A C T 5-3 The Formation of Ions in Water 148 5-4 Single-Replacement Reactions 150 5-5 Double-Replacement Reactions–Precipitation MAKING IT REAL: 146 147 153 Hard Water and Water Treatment 5-6 Double-Replacement Reactions–Neutralization PA R T B S U M M A R Y 161 Chapter Summary 162 Chapter Problems 164 1 47 158 159 CHAPTER 6 Quantities in Chemistry PA R T A 168 THE MEASUREMENT OF MASSES OF ELEMENTS AND COMPOUNDS 170 6-1 Relative Masses of Elements 170 6-2 The Mole and the Molar Mass of Elements 6-3 The Molar Mass of Compounds 177 PA R T A S U M M A R Y 181 PA R T B 173 THE COMPONENT ELEMENTS OF COMPOUNDS 182 6-4 The Composition of Compounds MAKING IT REAL: 182 Calcium in Our Diets—How Much Are You Getting? 6-5 Empirical and Molecular Formulas PA R T B S U M M A R Y 190 Chapter Summary 191 Chapter Problems 192 186 187 CHAPTER 7 Quantitative Relationships in Chemical Reactions 196 PA R T A M A S S R E L AT I O N S H I P S I N C H E M I C A L REACTIONS 198 7-1 Stoichiometry 198 7-2 Limiting Reactant 203 MAKING IT REAL: 7-3 Percent Yield Alcohol—The Limiting Reactant in Breathalyzers 208 PA R T A S U M M A R Y 210 207 xi MALO_FM_i-1_hr1.qxd xii 7-10-2008 17:03 Page xii CONTENTS PA R T B E N E R G Y R E L AT I O N S H I P S I N C H E M I C A L REACTIONS 211 7-4 Heat Energy in Chemical Reactions MAKING IT REAL: 213 214 PA R T B S U M M A R Y Chapter Summary Chapter Problems 211 Hydrogen—The Perfect Fuel 214 215 CHAPTER 8 Modern Atomic Theory PA R T A 220 TH E E N E R GY OF TH E E LECTR ON I N T H E AT O M 222 8-1 The Emission Spectra of the Elements and Bohr’s Model MAKING IT REAL: M A K I N G I T R E A L : Solving Crimes with Light 227 8-2 Modern Atomic Theory: A Closer Look at Energy Levels PA R T A S U M M A R Y 232 PA R T B 222 Roses Are Red; Violets Are Blue—But Why? 223 227 T H E P E R I O D I C TA B L E A N D E L E C T R O N C O N F I G U R AT I O N 233 8-3 Electron Configurations of the Elements 233 8-4 Orbital Diagrams of the Elements (Optional) 240 8-5 Periodic Trends 242 PA R T B S U M M A R Y 245 Chapter Summary 246 Chapter Problems 248 CHAPTER 9 The Chemical Bond PA R T A 252 C H E M I C A L B O N D S A N D T H E N AT U R E OF IONIC COMPOUNDS 254 9-1 Bond Formation and Representative Elements 9-2 Formation of Ions and Ionic Compounds 255 PA R T A S U M M A R Y 259 PA R T B 254 C H E M I C A L B O N D S A N D T H E N AT U R E OF MOLECULAR COMPOUNDS 260 9-3 The Covalent Bond 260 MAKING IT REAL: Nitrogen: From the Air to Proteins 263 9-4 Writing Lewis Structures 264 9-5 Resonance Structures 269 PA R T B S U M M A R Y 271 PA R T C THE DISTRIBUTION OF CHARGE IN CHEMICAL BONDS 272 MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xiii CONTENTS 9-6 9-7 9-8 9-9 Electronegativity and Polarity of Bonds Geometry of Simple Molecules 275 Polarity of Molecules 278 Formal Charge (Optional) 280 MAKING IT REAL: Enzymes—The Keys of Life 281 284 PA R T C S U M M A R Y Chapter Summary Chapter Problems 272 285 287 CHAPTER 10 The Gaseous State PA R T A 292 T H E N AT U R E O F T H E G A S E O U S S TAT E A N D T H E E F F E C T S O F CONDITIONS 294 10-1 The Nature of Gases and the Kinetic Molecular Theory M A K I N G I T R E A L : Ozone—Friend and Foe 296 10-2 The Pressure of a Gas 297 10-3 Charles’s, Gay-Lussac’s, and Avogadro’s Laws 301 PA R T A S U M M A R Y 309 PA R T B 294 R E L AT I O N S H I P S A M O N G Q U A N T I T I E S OF GASES, CONDITIONS, AND CHEMICAL REACTIONS 309 10-4 The Ideal Gas Law 310 10-5 Dalton’s Law of Partial Pressures 313 10-6 The Molar Volume and Density of a Gas MAKING IT REAL: 316 Defying Gravity—Hot-Air Balloons 319 10-7 Stoichiometry Involving Gases 319 PA R T B S U M M A R Y 321 Chapter Summary 322 Chapter Problems 324 CHAPTER 11 The Solid and Liquid States PA R T A 330 THE PROPERTIES OF CONDENSED S TAT E S A N D T H E F O R C E S I N V O LV E D 332 11-1 Properties of the Solid and Liquid States 332 11-2 Intermolecular Forces and Physical State 334 11-3 The Solid State: Melting Point 338 MAKING IT REAL: The Melting Point of Iron and the World Trade Center 341 PA R T A S U M M A R Y 342 xiii MALO_FM_i-1_hr1.qxd xiv 7-10-2008 17:03 Page xiv CONTENTS PA R T B T H E L I Q U I D S TAT E A N D C H A N G E S I N S TAT E 343 11-4 The Liquid State: Surface Tension, Viscosity, and Boiling Point 343 MAKING IT REAL: The Oceans of Mars 348 11-5 Energy and Changes in State 349 11-6 Heating Curve of Water 352 PA R T B S U M M A R Y 355 Chapter Summary 356 Chapter Problems 358 CHAPTER 12 Aqueous Solutions PA R T A 362 SOLUTIONS AND THE QUANTITIES I N V O LV E D 364 12-1 The Nature of Aqueous Solutions 364 12-2 The Effects of Temperature and Pressure on Solubility 367 MAKING IT REAL: Hyperbaric Therapy 369 12-3 Concentration: Percent by Mass 370 12-4 Concentration: Molarity 373 12-5 Stoichiometry Involving Solutions 377 PA R T A S U M M A R Y 381 PA R T B THE EFFECTS OF SOLUTES ON THE P R O P E R T I E S O F W AT E R 382 12-6 Electrical Properties of Solutions 382 12-7 Colligative Properties of Solutions 384 MAKING IT REAL: Osmosis in a Diaper PA R T B S U M M A R Y Chapter Summary Chapter Problems 389 390 390 392 CHAPTER 13 Acids, Bases, and Salts PA R T 13-1 13-2 13-3 13-4 A 396 A C I D S , B A S E S , A N D T H E F O R M AT I O N O F S A LT S 398 Properties of Acids and Bases 398 Brønsted–Lowry Acids and Bases 400 Strengths of Acids and Bases 404 Neutralization and the Formation of Salts MAKING IT REAL: 408 Salts and Fingerprint Imaging PA R T A S U M M A R Y 412 411 MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xv CONTENTS PA R T B THE MEASUREMENT OF ACID STRENGTH 412 13-5 Equilibrium of Water 13-6 The pH Scale 415 412 PA R T B S U M M A R Y PA R T C 419 S A LT S A N D O X I D E S A S A C I D S AND BASES 420 13-7 The Effect of Salts on pH—Hydrolysis 420 13-8 Control of pH—Buffer Solutions 423 MAKING IT REAL: The pH Balance in the Blood 13-9 Oxides as Acids and Bases MAKING IT REAL: 426 Acid Rain—The Price of Progress? PA R T C S U M M A R Y Chapter Summary Chapter Problems 425 428 428 429 431 CHAPTER 14 Oxidation–Reduction Reactions PA R T A 436 R E DOX R EACTIONS—TH E EXCHANG E 438 OF ELECTRONS 14-1 The Nature of Oxidation and Reduction and Oxidation States MAKING IT REAL: 438 Lightning Bugs (Fireflies)—Nature’s Little Night-Lights 14-2 Balancing Redox Equations: Oxidation State Method 444 14-3 Balancing Redox Equations: Ion-Electron Method 447 PA R T A S U M M A R Y 451 PA R T B S P O N TA N E O U S A N D N O N S P O N TA N E O U S R E DOX R EACTIONS 452 14-4 Predicting Spontaneous Redox Reactions 14-5 Voltaic Cells 457 MAKING IT REAL: 14-6 Electrolytic Cells 453 Fuel Cells—The Future Is (Almost) Here 462 PA R T B S U M M A R Y Chapter Summary Chapter Problems 464 465 466 CHAPTER 15 Reaction Rates and Equilibrium PA R T A 470 COLLISIONS OF MOLECULES AND R E A C T I O N S AT E Q U I L I B R I U M 472 15-1 How Reactions Take Place 472 15-2 Rates of Chemical Reactions 475 15-3 Equilibrium and Le Châtelier’s Principle MAKING IT REAL: 479 The Lake That Exploded PA R T A S U M M A R Y 484 483 462 443 xv MALO_FM_i-1_hr1.qxd xvi 7-10-2008 17:03 Page xvi CONTENTS PA R T B T H E Q U A N T I TAT I V E A S P E C T S O F R E A C T I O N S AT E Q U I L I B R I U M 485 15-4 The Equilibrium Constant 485 15-5 Equilibria of Weak Acids and Weak Bases in Water MAKING IT REAL: 15-6 Solubility Equilibria 496 497 PA R T B S U M M A R Y Chapter Summary Chapter Problems 489 Buffers and Swimming Pool Chemistry 502 502 505 CHAPTER 16 Nuclear Chemistry PA R T A 510 N A T U R A L LY O C C U R R I N G RADIOACTIVITY 512 16-1 Radioactivity 512 16-2 Rates of Decay of Radioactive Isotopes 16-3 The Effects of Radiation 518 MAKING IT REAL: 516 Radioactivity and Smoke Detectors 16-4 The Detection and Measurement of Radiation PA R T A S U M M A R Y 523 PA R T B 520 521 INDUCED NUCLEAR CHANGES AND THEIR USES 524 16-5 Nuclear Reactions 524 16-6 Applications of Radioactivity 526 16-7 Nuclear Fission and Fusion 529 MAKING IT REAL: Revisiting the Origin of the Elements PA R T B S U M M A R Y Chapter Summary Chapter Problems 534 535 537 C H A P T E R 17 ( W E B ) Organic Chemistry PA R T A w-2 HYDROCARBONS 17-1 Bonding in Organic Compounds 17-2 Alkanes w-8 17-3 Alkenes and Alkynes w-13 MAKING IT REAL: 17-4 Aromatic Compounds PA R T A w-4 w-4 The Age of Plastics w-17 SUMMARY w-19 w-16 534 MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xvii CONTENTS PA R T 17-5 17-6 17-7 17-8 B OTHER CLASSES OF ORGANIC COMPOUNDS W-20 Alcohols and Ethers w-20 Aldehydes and Ketones w-22 Amines w-24 Carboxylic Acids, Esters, and Amides MAKING IT REAL: w-28 w-29 PA R T B S U M M A R Y Chapter Summary Chapter Problems w-25 Aspirin—An Old Drug with a New Life w-30 w-32 CHAPTER 18 (WEB) Biochemistry PA R T A w-42 THREE BASIC TYPES OF BIOCHEMICAL COMPOUNDS w-44 18-1 Lipids w-44 MAKING IT REAL: Soap—Dissolves Away Fat 18-2 Carbohydrates w-49 18-3 Amino Acids and Proteins w-53 w-57 PA R T A S U M M A R Y PA R T B w-48 BIOCHEMICAL COMPOUNDS AND LIFE FUNCTIONS W-58 18-4 Enzymes w-58 18-5 Nucleic Acids and Genetics w-60 The Origin of Life MAKING IT REAL: w-65 PA R T B S U M M A R Y Chapter Summary Chapter Problems F O R E W O R D TO w-64 w-66 w-68 T H E A P P E N D I C E S APPENDIX A: B A S I C M AT H E M AT I C S APPENDIX B: BASIC ALG E B R A APPENDIX C: S C I E N T I F I C N O TAT I O N APPENDIX D: GRAPHS APPENDIX E: C A L C U L AT O R S APPENDIX F: G LOSSARY A-10 A-19 A-27 A-31 A-36 A P P E N D I X G : A N S W E R S TO C H A P T E R P R O B L E M S P H OTO C R E D I T S INDEX A-1 A-2 I-1 PC-1 A-45 xvii MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xviii MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xix P R E FA C E Leo Malone, sole author of the first seven editions, has joined forces with Ted Dolter to create Basic Concepts of Chemistry, Eighth Edition. Professor Dolter’s academic background in chemical education and professional duties as chairman of the chemistry program at Southwestern Illinois College uniquely qualifies him to integrate this new dimension of outcomes assessment into Basic Concepts of Chemistry. Although the new edition continues its focus on the preparatory and basic chemistry market, it now includes emphasis on chapter objectives and their assessment. Why Did We Write This Book? Basic Concepts of Chemistry was originally written in 1981 to address the needs of students planning to take the general chemistry course, but with little or no background in chemistry. Over the next seven editions, its mission has evolved, so that in this new eighth edition we have focused on integrating meaningful assessment and timely feedback into the book as well as the accompanying online course management course (WileyPLUS). This book has been used extensively in one semester, general-purpose courses, where professors find students at a variety of levels. For some of these students a main sequence in chemistry may follow, but for others the course precedes a semester of organic and biochemistry. Still others enroll to satisfy a science requirement or a one semester stand-alone chemistry requirement. The text was written at a level and with the functionality designed to accommodate the needs of each of these groups of students, by structuring itself so that an instructor could emphasize or omit certain clearly delineated sections. Basic Concepts of Chemistry Today Today, more and more students are entering post secondary education with a wider variety of learning styles and varied levels of preparedness. Recent data on student populations indicate that many of them are visual and kinesthetic learners and it is vital that textbook authors both recognize and integrate this pedagogy into their books. We have focused hard on accomplishing this goal. Furthermore, the students that take this course have very diverse math backgrounds and we have provided many valuable resources to allow those students with weak math skills to succeed in this course. To accommodate the visual and kinesthetic learner and to support those students with weaker math backgrounds, we have introduced several new features, principle among these is a focus on outcomes assessment. The Role of Outcomes Assessment in this Edition Surveys of programs across the country show that chemistry is being taught in numerous ways. From packed lecture halls to intimate classrooms, from Ph.D.s to adjunct instructors to teaching assistants, chemistry education is being delivered in multiple formats, often within the same institution. Outcomes Assessment is an xix MALO_FM_i-1_hr1.qxd xx 7-10-2008 17:03 Page xx P R E FA C E attempt to insure consistency in evaluating student achievement across these multiple formats. By delineating the expected outcomes or objectives for each chapter, and then devising assessment tools, such as homework and exam questions, lab experiments, group work, and the like, that are designed to target those specific objectives, schools can insure that all students in all sections are being served. By incorporating outcomes assessment into the curriculum, students can receive the same topical instruction and be evaluated against the same standard. Implementing and justifying an outcomes assessment program can be time consuming. To that end, the authors, having already been through an outcomes assessment program, have designed a text with objectives and assessments already in place, along with the required information needed to show how all of it ties together. Each Part within chapters includes a list of the relevant objectives for that chapter. PA R T A THE PROPERTIES O F M AT T E R OBJ ECTIVES SETTI NG A GOAL ■ You will learn how a sample of matter can be described by its properties and how they can be quantitatively expressed. 3-1 List and define several properties of matter and distinguish them as physical or chemical. 3-2 Perform calculations involving the density of liquids and solids. 3-3 (a) Describe the differences in properties between a pure substance and a mixture. (b) Perform calculations involving percent as applied to mixtures. These are measurable outcomes that the student should master by the completion of that part. Assessments of varying complexity follow each section so that the student, upon completion, can evaluate to what degree the material has been internalized. 4 - 3 ( a ) K N O W L E D G E : For which of the following metals must a charge be placed in parenthesis when naming one of its compounds? Co, Li, Sn, Al, Ba EXERCISE E X E R C I S E 4 - 3 ( b ) A N A LY S I S : (a) Li2O (b) CrI3 (c) PbS ASSESSING THE OBJECTIVE FOR SECTION 4-3 Name the following compounds. (d) Mg3N2 (e) Ni3P2 Provide the formula for the following chemicals. (c) tin(IV) bromide (d) calcium nitride E X E R C I S E 4 - 3 ( c ) A N A LY S I S : (a) aluminum iodide (b) iron(III) oxide Using an M to represent the metal and an X to represent the nonmetal, write theoretical formulas for all possible combinations of M and X with charges of 1, 2, 3 and 1, 2, and 3. EXERCISE 4-3(d) S Y N T H E S I S : For additional practice, work chapter problems 4-18, 4-20, 4-22, and 4-24. At the end of each chapter summary, there is an objectives grid which ties the objectives to examples within the sections, assessment exercises at the end each section, and relevant chapter problems at the end of each chapter. This grid has utility for both the student and instructor so that both can easily locate tools within the text to help address a specific student problem. MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xxi P R E FA C E OBJECTIVES SECTION YOU SHOU LD B E AB LE TO... EXAM PLES EXE RCISES CHAPTE R PROB LE MS 5-1 Write a chemical equation from a word description of the reaction. 5-1 1a, 1b, 1e, 2c 10, 11, 12, 13 Balance a simple chemical equation by inspection. 5-1, 5-2, 5-3 1c, 1d 2, 3, 4, 5 5-2 Classify certain chemical reactions as being combustion, combination, or decomposition reactions. 5-3 2a, 2b, 2c 14, 15, 16, 18, 19, 20, 21, 22, 23 5-3 Write the ions formed when ionic compounds or acids dissolve in water. 5-4 3a, 3b, 3c 24, 25, 26, 27 5-4 Given the activity series, complete several single-replacement reactions as balanced molecular, total ionic, and net ionic equations. 5-5 4a, 4b, 4c, 4d 28, 29, 30, 33 5-5 Given a table of solubility rules, determine whether a specific ionic compound is soluble or insoluble in water. 5-6 5a, 5b, 5c 34, 35, 40, 42 Write balanced molecular, total ionic, and net ionic equations for precipitation reactions. 5-7, 5-8, 5-9 5d, 5e 44, 45, 46, 47, 48, 49 Write balanced molecular, total ionic, and net ionic equations for neutralization reactions. 5-10 6a, 6b 55, 56, 57, 58 5-6 Other changes to the eighth edition include: • Emphasizing outcomes assessment, each Chapter Part now begins with Setting Goals, which serves to preview the important topics within that Part. Section Objectives are presented alongside these Goals so that students can realistically link the text’s goals to the objectives required of them. • Assessing the Objectives are a collection of problems that appear at the end of each section, and provide students with the opportunity to assess their understanding of each section’s objectives. The representative problems are divided into three cognitive levels: Knowledge, Analysis, and Synthesis. Each level is progressively more sophisticated and prompts the students to gauge their conceptual understanding of the section content. • Every concept in the text is clearly illustrated with one or more step by step examples. Most examples, in addition to a Procedure and Solution step, are followed by two new steps Analysis and Synthesis. The Analysis step discusses the problem in light of the reasonableness of the answer, or perhaps suggests an alternate way to solve the problem involving different learning modes. The concluding Synthesis step gives the student the opportunity to delve deeper, asking the student to extend their knowledge. These added steps promote critical thinking and facilitate deeper conceptual understanding. • Making it Real essays have been updated to present timely and engaging realworld applications, emphasizing to the student the relevance of the material they are learning. For example, in the high-interest field of forensics we describe how glass shards from crime scenes can be identified by their density in Chapter 3, and then in Chapter 8, explore how the refractive index of glass is also used as important evidence in solving crimes. In Chapter 7, we take a look at the chemical reactions involved in the breathalyzer and in Chapter 13, how salts are used to analyze fingerprints. • New to this edition are end of chapter Student Workshop activities. These are intended to cater to the many different student learning styles and to engage them in the practical aspect of the material discussed in the chapter. Each “Student Workshop” includes a statement of purpose and an estimated time for completion. xxi MALO_FM_i-1_hr1.qxd xxii 7-10-2008 17:03 Page xxii P R E FA C E Organization The Prologue is a unique feature which introduces the origin of science in general and chemistry in particular. There are no quizzes, exercises, or problems; rather, it is meant to be a relaxing, historical glimpse at the origin of this fascinating subject and how it now affects our lives. Our intent is build interest and engage the student in further study. We recognize the changing needs of students and balance that with the requirements to successfully study chemistry. As such, we continue to provide the necessary support for students continuing on in the study of chemistry. Chapter 1, Measurements in Chemistry, provides the necessary math tools in a nonthreatening way. In Chapter 2, Elements and Compounds, the elements are introduced starting from what we see and sense about us (the macroscopic) to the atoms of which they are composed and finally into the structure within the atom (the microscopic and submicroscopic.) We do the same for compounds in the second part of this chapter. Chapter 3, The Properties of Energy and Matter continues the discussion of matter and its properties. Some additional yet relevant math concepts such as density, percent composition, and specific heat are introduced in this chapter as properties of matter. Chapter 4, The Periodic Table and Chemical Nomenclature, allows us to draw in one of the primary tools of the chemist, the periodic table. We see its functionality and organization, and begin using it in a thorough discussion of how to name most common chemicals, whose structure was discussed in chapter 2. In Chapter 5, Chemical Reactions we discuss the broad range of chemical interactions that can occur. The quantitative aspects of chemistry are discussed in Chapter 6, Quantities in Chemistry and Chapter 7, Quantitative Relationships in Chemical Reactions. These chapters were split from a single, larger chapter in the 7th edition, and have been moved forward ahead of Chapter 8, Modern Atomic Theory and Chapter 9, The Chemical Bond. Still, the two latter chapters can be moved ahead of Chapter 5 without prejudice, depending on the preferences of the instructor, and the ease with which the material can be incorporated into the overall curriculum. Chapter 10, The Gaseous State, begins a three chapter in depth study of the states of matter by examining the unique and predictable behaviors of gases. This is followed by similar discussions of the condensed states of matter in Chapter 11, The Liquid and Solid States, which includes a thorough but understandable discussion of intermolecular forces and how those affect the properties of matter. This discussion continues in Chapter 12, Aqueous Solutions, where we discuss both the qualitative and quantitative aspects of solute-solvent interactions. This chapter serves as a wrap-up of the quantitative relationships introduced in Chapters 6 and 7. Chapter 13, Acids, Bases and Salts, begins a discussion of specific classes of chemicals, and goes into depth as regards the ways acids and bases can react together and with their environment. A second class of reaction is explored in depth in Chapter 14, Oxidation-Reduction Reactions. The relationship of these types of reactions to the creation of batteries and electrical currents is explained. The remaining chapters offer a survey of topics that are of general chemical interest, and are appropriate for those looking to expose their students to a broad set of topics. Chapter 15, Reaction Rate and Equilibrium, introduces the concepts of Kinetics and Equilibrium and gives a taste of the sophisticated mathematical treatment these topics receive. Chapter 16, Nuclear Chemistry, explores how radioactivity is a phenomenon associated with certain elements and isotopes. Chapter 17, Organic Chemistry, gives the briefest introduction to organic functional groups, structure, and bonding. Chapter 18, Biochemistry, gives a similar treatment to common biochemical structures like carbohydrates, proteins, lipids, and nucleic acids. MALO_FM_i-1_hr1.qxd 8-10-2008 15:27 Page xxiii P R E FA C E Supplements WileyPLUS with CATALYST WileyPLUS is a powerful online tool that provides a completely integrated suite of teaching and learning resources on one easy to use website. WileyPLUS integrates Wiley’s world-renowned content with media, including a multimedia version of the text, PowerPoint slides, digital image archive, online assessment, and more. WileyPLUS with CATALYST partners with the instructor to teach students how to think their way through problems, rather than rely on a list of memorized equations, by placing a strong emphasis on developing problem solving skills and conceptual understanding. WileyPLUS with CATALYST incorporates an online learning system designed to facilitate dynamic learning and retention of learned concepts. CATALYST was developed by Dr. Patrick Wegner (California State University, Fullerton) to promote conceptual understanding and visualization of chemical phenomena in undergraduate chemistry courses. CATALYST assignments have multiple levels of parameterization and test on key concepts from multiple points of view (visual, symbolic, graphical, quantitative). Hundreds of end-of-chapter problems are available for assignment, and all are available with multiple forms of problemsolving support. Study Guide/Solutions Manual by Leo J. Malone is available to accompany this text. In the Study Guide/Solutions Manual, the same topics in a specific section are also grouped in the same manner for review, discussion, and testing. In this manner, the Study Guide/Solutions Manual can be put to use before the chapter is completed. The Study Guide/Solutions Manual contains answers and worked-out solutions to all problems in green lettering in the text. Experiments in Basic Chemistry by Steven Murov and Brian Stedjee, Modesto Junior College. Taking an exploratory approach to chemistry, this hands-on lab manual for preparatory chemistry encourages critical thinking and allows students to make discoveries as they experiment. The manual contains 26 experiments that parallel text organization and provides learning objectives, discussion sections outlining each experiment, easy-to-follow procedures, post-lab questions, and additional exercises. Instructor’s Manual and Test Bank by Leo J. Malone, St Louis University; Ted Dolter and Steve Gentemann, Southwestern Illinois College; and Kyle Beran, University of TexasPermian Basin. The Instructor’s Manual consists of two parts; the first part includes hints and comments for each chapter by Ted Dolter, followed by daily lesson plans by Steve Gentemann. The second part of the manual contains answers and worked-out solutions to all chapter-end problems in the text by Leo Malone. The test bank by Kyle Beran consists of multiple choice, short answer, and fill in the blank questions. Instructor’s Manual for Experiments in Basic Chemistry, written by the lab manual authors, contains answers to post-lab questions, lists of chemicals needed, suggestions for other experiments, as well as suggestions for experimental set-ups. Power Point Lecture Slides, created by Wyatt Murphy, of Seton Hall University, these slides contain key topics from each chapter of the text, along with supporting artwork and figures from the text. The slides also contain assessment questions that can be used to facilitate discussions during lecture. Digital Image Archive. The text web site includes downloadable files of text images in JPEG format. Computerized Test Bank The IBM and Macintosh compatible version of the entire Test Bank has full editing features to help the instructor customize tests. Most of the resources listed above can also be accessed at www.wiley.com/ college/malone. xxiii MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xxiv MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xxv A C K N O W L E D G M E N T S A revision of this magnitude involves efforts spanning several years and requiring the input of many people. In particular, Dr. Malone thanks his colleagues at Saint Louis University for their helpful comments in previous editions of this text. He’s grateful to his wife Meg, who demonstrated patience and put up with occasional crabbiness during the new text’s preparation. Dr. Malone also appreciates the support of his children and their spouses: Lisa and Chris, Mary and Brian, Katie and Rob, and Bill. They and their eleven children were both a source of great inspiration and a large amount of noise. Professor Dolter thanks his general chemistry instructor, who provided a sound understanding of the basic principles needed in forming his craft. Although his professor (LJM) was a taskmaster, the end result was worth it. He’d also like to thank his colleagues at SWIC, who happily allowed him to bounce ideas off of them, and delighted in giving their advice. Professor Dolter is thankful for his wife Peggy, who endured the single-parent lifestyle many weekends during the writing of this text. A nod also goes to, Isabel and Zachary, who wondered if their dad was ever going to finish this book; they’re owed some dad-time. The authors also wish to thank the many people at John Wiley who helped and encouraged this project, especially Joan Kalkut for keeping us moving. In addition, we’d like to thank Nick Ferrari, our editor, for his support of this revision; Jennifer Yee, our supplements editor; Cathy Donovan, chemistry assistant extraordinaire; photo researcher, Lisa Gee; and Suzanne Ingrao of Ingrao Associates, who kept an eye on every production detail, and kindly made sure we kept on schedule. Kevin Murphy and Brian Salisbury did a wonderful job of creating the new design, which highlights the Outcomes Assessment focus of the text. Thank you all for remaining wonderfully patient in the face of missed deadlines and family conflicts. Finally, the following people offered many useful comments and suggestions for the development of the Eighth Edition: Jeanne C. Arquette, Phoenix College Gerald Berkowitz, Erie Community College Ken Capps, Central Florida Community College Brant Chapman, Bergen Community College Douglas S. Cody, Nassau Community College John J. Dolhun, Norwalk Community College Danae Quirk Dorr, Minnesota State University, Mankato Rob Fremland, San Diego Mesa College Amy Grant, El Camino College Paul R. Haberstroh, Mohave Community College Mary Hadley, Minnesota State University Alton Hassell, Baylor University Bettina Heinz, Palomar College Bruce E. Hodson, Baylor University Tracy Holbrook, Cape Fear Community College Larry Kolopajlo, Eastern Michigan University Virginia R. Kotlarz, Erie Community College Rosemary Leary, Estrella Community College Rich Lomneth, University of Nebraska at Omaha Kathy Mitchell, St. Petersburg College Krzysztof Ochwat, Wilbur Wright College Neil Palosaari, Inver Hills Community College Todd Rogers, Columbia Basin College Leo J. Malone Saint Louis University Theodore O. Dolter Southwestern Illinois College xxv MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xxvi MALO_FM_i-1_hr1.qxd 7-10-2008 17:03 Page xxvii BASIC CONCE PTS OF CH E M ISTRY MALO_c00_002-013hr.qxd 7-10-2008 10:58 Page 2 P R O L O G U E Science and the Magnificent Human Mind hat could be more peaceful than a campfire silhouetted by the night sky? Actually, the sky and the fire were the source of remarkable achievements of the human race but in different ways. Observations of the sky and the stars provided the keys, in an ongoing process, that are unlocking the secrets of space, time, and the history of the cosmos. The use of fire, an awesome force of nature, provided the protection and the warmth that allowed the human race to thrive in a hostile world. Eventually, the use of fire would be the instrument of huge advances in civilization. The Prologue relates how the study of the stars and the use of fire led us to the world of science that serves us so ably today. W MALO_c00_002-013hr.qxd A B C 9-09-2008 13:41 The Origin of Matter The Mystery of Fire The Scientific Method Page 3 A M O N G T H E A N I M A L K I N G D O M , only humans have the ability to take their minds beyond simple survival. We also analyze, ponder, and predict the future based on observations. This has led us to a remarkable understanding of all that we see and otherwise sense about us. So this Prologue is dedicated to how the wonderful workings of our minds have allowed us to establish the realm of modern science. In Section A, we examine how the first stirrings of curiosity about the night sky led eventually to the still developing understanding of what has happened since the beginning of time. As presented here, we are preempting the use of some terms and concepts that will be explained more thoroughly in later chapters. The readings in the Prologue are meant to tweak your interest, not necessarily to be learned. In Section B, we see how the taming of fire by our ancient ancestors propelled us into huge scientific discoveries and the basis of chemistry. Finally, in Section C, we take note of how science in general and chemistry in particular have progressed from random discoveries and serendipity to the complex technical world in which we exist today. After proceeding through the Prologue, we will build the topic of chemistry from the most basic substances of the universe to the complex world of chemistry that serves us in so many ways today. 3 MALO_c00_002-013hr.qxd 4 9-09-2008 PROLOGUE 13:41 Page 4 Science and the Magnificent Human Mind A T H E O R I G I N O F M AT T E R Somewhere in ancient time, many thousands of years ago, someone looked up at the night sky and wondered what this display of bright dots meant. It was a great landmark in our existence, as humans became able to expand their minds beyond just the concerns of everyday survival and existence. With the power of abstract reasoning, our earliest ancestors began to observe, consider, and speculate about the world around them. Surely the glittering display of bright stars in the heavens would have attracted the attention of their newly inquisitive minds. One can only imagine what they must have thought they were observing. They probably sensed that something very vast and mysterious was involved, but they would not have known that the secrets of our very existence are indeed “written in the stars.” What cosmologists have garnered from the night sky in just the past few decades has given us a tantalizing yet still incomplete understanding of the beginning, evolution, and ultimate destiny of our entire universe. From observations of the cosmos, many of the mysteries of the origin of all that we see, from the paper in front of us to the farthest reach of the cosmos in infinite space, have been revealed. On a small piece of dust in the universe, called Earth, we peer out into distant space and back into ancient time. We observe the flickering points of light that we call stars—the visible flashes from distant suns, some like our own. Magnification of the heavens tells us that some of what appear as individual stars to the naked eye are actually groups of stars called galaxies, each containing hundreds of billions of individual stars. It was the motions of these galaxies in the heavens that provided modern scientists with the clues about the origin of everything. One observation divulged that groups of galaxies seem to be pushing away from each other, indicating a dynamic, continually expanding universe. A logical conclusion from this is that the galaxies were closer together in the past. In fact, if we go back a little less than 14 billion years, the entire cosmos was coalesced into a single, infinitely dense point known as the singularity. The spontaneous expansion of this point (which is referred to as “the big bang”) marked the beginning of time and space. At the very start of time, the two components of the universe—the stars, planets, and other forms of matter (which has mass) as well as the heat, light, and other forms of energy (which has no mass)— were to evolve from the singularity. How the singularity came to be and what was present before time began is unknown to science and may never be known. But, immediately after the big bang, there was only energy and unbelievable heat. It wasn’t for another 10,000 years that our infant universe expanded and cooled enough so that some of the energy of this nascent system evolved into the basic building blocks of nature. The first matter was composed of three basic particles known as protons, neutrons, and electrons, which evolved from energy and even more fundamental particles. At first they existed independently in the hot, dense universe. These particles exist in the world of the submicroscopic—they are way too small to see with even the most powerful magnification. The proton carries a positive electrical charge; the neutron, about the same mass as a proton, carries no charge. The third particle, the electron, tiny compared to protons and neutrons (about 1/2000 the mass), carries a negative charge equal but opposite to the charge on the proton. From these three particles, the entire stuff of the universe would eventually evolve. About 400,000 years after the big bang, a hugely significant event occurred. The particles slowed down enough so that the attractive forces between a positively charged proton and a negatively charged electron could hold the two particles MALO_c00_002-013hr.qxd 9-09-2008 13:41 Page 5 A The Origin of Matter together. Significantly, the electron and proton did not directly attach to each other. Instead, the electron settled into a stable orbit around the central proton. Why this happened is not easily explained but is understood in the realm of quantum mechanics. Quantum mechanics is the science that deals with the forces involved in the very small dimensions of these particles. For now we can accept some results of more complex theories without going into detail. A model of the hydrogen atom, with an electron in a set orbit, was first advanced by Niels Bohr in 1923. It compares the orbiting of the electron around the proton to the motion of the Earth around the sun. In fact, the nature of the electron in the atom is now known to be more complex, but this classical orbiting model serves us well at this point, so we will use it. The proton and the electron together now formed a neutral atom. Normal matter is composed of variations of these tiny particles called atoms. The smallness of atoms is a stretch for the human mind to comprehend. In fact, the period at the end of this sentence contains a number of atoms comparable to the number of grains of sand in the Sahara Desert (about 1017, or one hundred million billion atoms). The proton is the center of this tiny two-particle universe and is known as the nucleus of the atom. The vast volume of the atom is empty space in which the electron exists. If the minute size of the atom isn’t hard enough to imagine, the dimensions within the atom itself are equally difficult for our modest and limited minds to fathom. Imagine that the nucleus was the size of a basketball. In that case, the electron, which defines the total size of the atom, would exist in a volume with a two-mile radius. This model represents an atom of the element hydrogen, which accounted for 90% of the atoms initially formed in the big bang. An element is a basic form of matter. – Hydrogen atom + What of the other 10% of the matter that was formed? Some of the nuclei of hydrogen contained one neutron as well as one proton. This form of hydrogen is often referred to as deuterium or heavy hydrogen, but it is not a unique element. About one out of 30,000 hydrogen atoms are actually deuterium atoms. Atoms of a certain element that have a specific number of neutrons are known as isotopes. So, initially, the element hydrogen existed as a mixture of two isotopes, normal hydrogen and a very small amount of deuterium. The earliest universe contained another type of nucleus that had two protons and two neutrons. When combined with two electrons, these nuclei formed the atoms of a second element known as helium. The atoms of a specific element have a definite number of protons in the nucleus, and that is what determines the identity of an element. At this point in time, essentially only two elements, hydrogen and helium, existed in the entire cosmos. It is believed that there may also have been trace amounts of a third element, known as lithium, among the first atoms formed after the big bang. Lithium is identified by the presence of three protons along with four neutrons in the 5 MALO_c00_002-013hr.qxd 6 9-09-2008 PROLOGUE 13:41 Page 6 Science and the Magnificent Human Mind nuclei of its atoms. The three other atoms in the primeval universe are illustrated below. – + ++ – – Deuterium Helium D, He, Li + ++ – – – Lithium Chemistry makes use of a good amount of convenient symbolism. The elements are represented by symbols that are usually the first one or two letters of their English, Latin, or, in one case, German, names. Thus H stands for hydrogen, He for helium, and Li for lithium. To represent the information about the content of an isotope’s nucleus, we use isotopic notation. The number in the upper-left-hand corner is known as the mass number, which is the total number of protons and neutrons. The number in the lower-left-hand corner is the atomic number, which is the number of protons in that specific element. The atomic number and the element’s symbol are redundant because each element has a specific atomic number. 1 1H 2 1H 4 2He 7 3Li The complete list of elements, along with their symbols, is shown inside the front cover. For a time after the formation of the original neutral atoms, the universe turned completely dark. However, about 1 billion years after the big bang, some of the hydrogen and helium began to gather into individual clouds of gas. We are not sure why this happened, but it did. However, this was a significant event because within the regions of gas, an elementary attractive force of nature, gravity, began to have its way. Gravity caused some of the individual clouds of gas to contract. Changes began to occur in the clouds as the atoms moved closer together. As the clouds contracted, the temperature within increased dramatically. Heat relates to the velocity of the atoms. Heat causes expansion, which actually counteracts gravity. However, gravity continued to predominate in the huge cloud, so further contraction and heating occurred. Crushing pressures and high temperature began to build in the center of the cloud. In the dynamic, churning center of the cloud, the extremely hot hydrogen nuclei, now stripped of their orbiting electrons, collided frequently with each other. However, the fact that they had the same electrical charge meant that they actually MALO_c00_002-013hr.qxd 9-09-2008 13:41 Page 7 A The Origin of Matter did not touch but were repelled from each other (like charges repel; unlike charges attract). At some point, however, a phenomenal event happened in the evolution of our cosmos. Colliding protons had enough velocity and energy to overcome the repulsive forces between the two nuclei, thus merging or fusing together to form a single nucleus. This process is called nuclear fusion. Some of the mass of the two fusing nuclei converted back into energy (i.e., Einstein’s law, E = mc2). It was like starting a campfire. Once the fire starts, it continues until the wood is consumed. The heat generated from the fusion of the atoms within the cloud was enough to counteract the pull of gravity, thus stabilizing the size of the cloud. The cloud of gas began to glow and, at that time, a star was born. The universe began to light up and appear much like we see it today, except that the stars were much closer together. (See Figure P-1.) Fusion powers all of the stars, including our own sun. (Nuclear fusion has only been understood since the late 1930s.) + 2 H A Typical Star Our sun is a typical star, generating massive amounts of energy from the fusion of hydrogen to form helium. FIGURE P-1 ++ + Deuterium fusion 4 2He 2 H The fusion of protons to form helium occurs in several steps that are somewhat complex. The fusion of deuterium nuclei to form a helium nucleus, which was mentioned previously, however, occurs in one simple step and is illustrated below. Many of the earliest stars were massive (many times larger than our own sun) and used up their hydrogen fuel in the core of the star in the course of several million years. Our own sun uses its fuel much more slowly, so even though it is over 4 billion years old, it will go on at this rate for many more billion years. So far, however, in our early universe, the number of elements had not changed—just a minuscule increase in the amount of helium as a result of fusion. It is what happened next in the stars that led to the formation of heavier elements. As the supply of hydrogen began to diminish in the core of the star, the fusion of protons began to wane and no longer supplied enough energy to keep the size of the star stable. So again gravity predominated and contraction recommenced. With the increasing pressure came increasing temperatures. Eventually the heat was high enough and the nuclei crushed together enough to cause the helium nuclei (with a ⫹2 charge) to fuse to form the first elements heavier than lithium. (Stars in this stage are known as red giants.) This process occurs at a higher temperature than the proton fusion because of the higher nuclear charge to be overcome by the colliding nuclei. The fusion of helium in a series of steps eventually led to heavier elements such as carbon (mass number 12) and oxygen (mass number 16). In time, the helium was exhausted and the contraction-heating process took over once again. Another stage of elemental formation would begin, forming even heavier elements such as aluminum and silicon. Each stage of this cycle was a result of higher temperatures and higher pressures within the star and led to the creation of heavier and heavier elements. 7 MALO_c00_002-013hr.qxd 8 9-09-2008 PROLOGUE Page 8 Science and the Magnificent Human Mind A Supernova The bright star in the center of the photo is actually an exploding star. Heavy elements are being formed in this explosion. FIGURE P-2 13:41 This process of fusion, contraction, higher temperature, and pressure followed by more fusion only goes so far. The fusing of lighter elements to form elements up to the mass of iron (26 protons and 30 neutrons) releases energy. Formation of any element heavier than that does not release energy, so the fusion process stops abruptly at that point. It is as if iron forms the ashes of the nuclear fire. When a fire is reduced to ashes, the fire goes out. However, in the stepwise evolution of a star, the first 26 or 27 elements were formed. Yet we have many other familiar elements that are much heavier than iron, such as gold and uranium. What is their origin if not from the interior of a star? The spectacular results of what happens when a huge star exhausted the fuel in its now mainly iron core is what produced the heaviest of the elements. Other messages from space have given us insight into creation of the heavier elements. In 1987, an extremely bright star was found in the heavens from an observatory in Chile. Only an ordinary dim star had been there the night before. The astronomers became immediately aware that they were witnessing the explosion of a star known as a supernova. (See Figure P-2.) This phenomenon had been previously known but was now being witnessed. Apparently, the star had suddenly exhausted the supply of fuel for fusion in its core. Without an energy source to counteract gravity, the star again collapsed. This time the collapse did not stop, causing densities, temperatures, and pressures to go to the extreme. But in a matter of seconds, the collapsing star rebounded in a cataclysmic explosion, propelling the outer layers of the star into outer space along with a huge flux of neutrons (formed when electrons are forced into a proton). Elements such as iron dramatically increased their mass by adding neutrons during and after the explosion. The more massive atoms formed at this time eventually underwent nuclear changes that produced elements with higher and higher atomic numbers such as silver, lead, and gold. To summarize the sequence of events: (1) A star explodes, sending elements formed by fusion in the star rushing into space along with huge numbers of neutrons. (2) The atoms of the original elements absorb neutrons, increasing the atomic mass. (3) The heavier elements undergo nuclear changes, leading to elements with high atomic numbers. (The heaviest naturally occurring element found on Earth is uranium-238.) For billions of years, giant clouds of hydrogen have formed and contracted into new generations of stars. Each generation had more and more of the heavier elements. (In fact, astronomers have identified stars with few heavy elements, indicating that they date to near the beginning of time.) Blasted by the force of supernovae, this matter drifted through cold, dark space. About 4.6 billion years ago, a cloud of hydrogen containing the dust and debris from previous stars condensed to form our sun, with enough star dust left over to form eight (or more) planets and many other smaller solid bodies trapped in perpetual orbits around this star. On the third planet out from this ordinary star, atoms of some of the lighter elements assembled into living systems. It sounds somewhat melodramatic, but we are indeed children of the stars. The Origin of the Chemical Bond So far, we have encroached into the disciplines of astronomy and physics. Chemistry came into being when atoms began to bond to each other. Let’s return to the early universe, about the time clouds of neutral hydrogen atoms (nuclei and orbiting electrons) were beginning to form. At first, the new hydrogen atoms were very hot. When two hydrogen atoms collided, they bounced away from each other like recoiling billiard balls. When they cooled sufficiently, however, another important event occurred. The two neutral atoms stuck together. The electrons of the two atoms acted like glue, holding the two atoms together. The sharing of electrons between two atoms is known as a covalent chemical bond or simply a chemical bond. If it weren’t for the fact that two atoms are more stable bonded together than existing apart, the universe would still be just a collection of MALO_c00_002-013hr.qxd 9-09-2008 13:41 Page 9 B The Mystery of Fire 9 gaseous atoms—no continents, no oceans, no moons, no us. The two hydrogen atoms joined together to form a molecule. A molecule is composed of two or more atoms chemically bonded together. This is illustrated by the formula H2, where the subscript 2 indicates the number of hydrogen atoms present in the molecule. The hydrogen molecule is the primeval molecule. It is the way hydrogen exists except at a very high temperature that forces the atoms apart. As the universe became enriched in other elements, chemical bonds formed between other elements. In the farthest reaches of space, we have detected many other molecules that have formulas such as H2CO (formaldehyde whose molecules contain two hydrogens, one carbon, and one oxygen), HCN (hydrogen cyanide), H2O (water), NH3(ammonia), and even more complex species. Like the primeval molecule, H2, the atoms in these molecules are held together by chemical bonds. (There is another type of bond that held lithium and hydrogen together in the early universe called an ionic bond. It will be described in Chapter 2.) On Earth, we find molecules ranging from the simplest two-atom hydrogen molecule to those of DNA, which contain millions of atoms. In Chapter 1, we begin our journey into chemistry by emphasizing mathematical skills related to chemistry. In Chapter 2, we then examine the types of matter found in our beautiful planet with its air, oceans, and solid earth. We will then develop and master the topic one step at a time while continuing to emphasize the “big picture.” B THE MYSTERY OF FIRE At about the same time (give or take 100,000 years) that humans may have started to wonder about the meaning of the night sky, they did something more immediately practical with their new ability to reason. It would change their destiny and order in the realm of all other animals. They tamed and put to use one of the most powerful forces in nature: fire. It is difficult to imagine how our ancient ancestors could have managed without fire. Humans do not have sharp night vision like the raccoon, but fire brought light to the long, dark night. We have no protective fur like the deer, but fire lessened the chill of winter. We do not have sharp teeth or powerful jaws like the lion, but fire rendered meat tender. Humans are not as strong or as powerful as the other large animals, but fire repels even the most ferocious of beasts. It seems reasonable to suggest that the taming of fire was one of the most monumental events in the history of the human race. The use of fire made our species dominant over all others. Let’s fast-forward in time to near the end of the Stone Age, about 10,000 years ago, when fire became the agent that launched us into the world of chemistry. In the Stone Age, weapons and utensils were fashioned from rocks and a few chunks of copper metal (an element) that were found in nature. Copper was superior to stone because pounding could easily shape it into fine points and sharp blades. Unfortunately, native copper was quite rare. But about 7000 years ago this changed. Anthropologists speculate that some resident of ancient Persia found copper metal in the ashes remaining from a hot charcoal fire. The free copper had not been there before, so it must have come from a green stone called malachite (see Figure P-3), which probably lined the fire pit. Imagine the commotion that this discovery must have caused. Hot coals could transform a particular stone into a valuable metal. Fire was the key that launched the human population into the age of metals. The recovery of metals from their ores is now a branch of chemical science called F I G U R E P - 3 Malachite Malachite is a metallurgy. The ancient Persians must have considered this discovery a dra- copper ore. When heated with charcoal, it matic example of the magic of fire. forms metallic copper. MALO_c00_002-013hr.qxd 10 9-09-2008 PROLOGUE 13:41 Page 10 Science and the Magnificent Human Mind Other civilizations used chemistry in various ways. About 3000 B.C., the Egyptians learned how to dye cloth and embalm their dead through the use of certain chemicals found in nature. They were very good at what they did. In fact, we can still determine from ancient mummies the cause of death and even diseases the person may have had. The Egyptians were good chemists, but they had no idea why any of these procedures worked. Every chemical process they used was discovered by accident. Around 400 B.C., while some Greeks were speculating about their various gods, philosophers were trying to understand and describe nature. These great thinkers argued about why things occurred in the world around them, but they were not inclined (or able) to check out their ideas by experimentation or to put them to practical use. At the time, however, people believed that there were four basic elements of nature—earth, air, water, and fire. Everything else was simply a specific combination of these basic elements. Of the original four elements, fire was obviously the most mysterious. It was the transforming element; that is, it had the capacity to change one substance into another (e.g., certain rocks into metals). We now call such transformations “chemistry.” Fire itself consists of the hot, glowing gases associated with certain chemical changes. If fire is a result of an ongoing chemical transformation, then it is reasonable to suggest that chemistry and many significant advances in the human race are very much related. The early centuries of the Middle Ages (A.D. 500–1600) in Europe are sometimes referred to as the Dark Ages because of the lack of art and literature and the decline of central governments. The civilizations that Egypt, Greece, and Rome had previously built began to decline. Chemistry, however, began to grow during this period, especially in the area of experimentation. Chemistry was then considered a combination of magic and art rather than a science. Many of those who practiced chemistry in Europe were known as alchemists. Some of these alchemists were simply con artists who tried to convince greedy kings that they could transform cheaper metals such as lead and zinc into gold. Gold was thought to be the perfect metal. Such a task was impossible, of course, so many of these alchemists met a drastic fate for their lack of success. However, all was not lost. Many important laboratory procedures such as distillation and crystallization were developed. Alchemists also discovered or prepared many previously unknown chemicals, which we now know as elements and compounds. Modern chemistry has its foundation in the late 1700s when the use of the analytical balance became widespread. Chemistry then became a quantitative science in which theories had to be correlated with the results of direct laboratory experimentation. From these experiments and observations came the modern atomic theory, first proposed by John Dalton around 1803. This theory, in a slightly modified form, is still the basis of our understanding of nature today. Dalton’s theory gave chemistry the solid base from which it could serve humanity on an impressive scale. Actually, most of our understanding of chemistry has evolved in the past 100 years. In a way, this makes chemistry a very young science. However, if we mark the beginning of chemistry with the use of fire, it is also the oldest science. From the ancient Persians five millennia ago, to the Egyptians, to the alchemists of the Middle Ages, various cultures have stumbled on assorted chemical procedures. In many cases, these were used to improve the quality of life. With the exception of the Greek philosophers, there was little attention given to why a certain process worked. The “why” is very important. In fact, the tremendous explosion of scientific knowledge and applications in the past 200 years can be attributed to how science is now approached. This is called the scientific method, which we will discuss next. C THE SCIENTIFIC METHOD In ancient times, scientific advances were discovered by accident. This still occurs to some extent, but we have made great strides in how we approach science such that most modern advances occur by design. Consider the case of tamoxifen, a chem- MALO_c00_002-013hr.qxd 9-09-2008 13:41 Page 11 C The Scientific Method 11 ical that is saving the lives of thousands of women in the United States alone. It is thought to dramatically reduce the chances of recurrence of breast cancer, a frightening disease that now strikes about one in nine American women. In 1998, the Food and Drug Administration (FDA) approved use of the drug to prevent breast cancer in women with a high risk of the disease. But the drug also has undesirable side effects. It may increase the chances of other types of cancer in some women and, in a few cases, causes depression, irritability, and short-term memory loss. However, knowing how tamoxifen works led scientists to produce an improved drug. In December 2004, the drug anastrazole was found to be at least as effective as tamoxifen but with fewer side effects. It is now under large-scale testing. How tamoxifen was discovered in the first place and what led to the potentially improved drug are examples of how the scientific method improves our lives. But the first step in the scientific method is a long way from producing a useful drug. It simply involves making observations and gathering data. As an example, imagine that we are the first to make a simple observation about nature—“the sun rises in the east and sets in the west.” This never seems to vary and, as far as we can tell from history, it has always been so. In other words, our scientific observation is strictly reproducible. So now we ask “Why?” We are ready for a hypothesis. A hypothesis is a tentative explanation of observations. The first plausible hypothesis to explain our observations was advanced by Claudius Ptolemy, a Greek philosopher, in A.D. 150. He suggested that the sun, as well as the rest of the universe, revolves around the Earth from east to west. That made sense. It certainly explained the observation. In fact, this concept became an article of religious faith in much of the Western world. However, Ptolemy’s hypothesis did not explain other observations known at the time, which included the movement of the planets across the sky and the phases of the moon. Sometimes new or contradictory evidence means a hypothesis, just like a brokendown old car, must either receive a major overhaul or be discarded entirely. In 1543, a new hypothesis was proposed. Nicolaus Copernicus explained all of the observations about the sun, moon, and planets by suggesting that Earth and the other planets orbit around the sun instead of vice versa. Even though this hypothesis explained the mysteries of the heavenly bodies, it was considered extremely radical and even heretical at the time. (It was believed that God made Earth the center of the universe.) In 1609, a Venetian scientist by the name of Galileo Galilei built a telescope to view ships still far out at sea. When he turned the telescope up to the sky, he eventually produced almost unquestionable proof that Copernicus was correct. Galileo is sometimes credited with the beginning of the modern scientific method because he provided direct experimental data in support of a concept. The hypothesis had withstood the challenge of experiments and thus could be considered a theory. A theory is a well established hypothesis. A theory should predict the results of future experiments or observations. The next part of this story comes in 1684, when an English scientist named Sir Isaac Newton stated a law that governs the motion of planets around the sun. A law is a concise scientific statement of fact to which no exceptions are known. Newton’s law of universal gravitation states that planets are held by gravity in stationary orbits F I G U R E P - 4 The Solar System The Copernican theory became the basis of a natural law of the universe. around the sun. (See Figure P-4.) MALO_c00_002-013hr.qxd 12 9-09-2008 PROLOGUE 13:41 Page 12 Science and the Magnificent Human Mind In summary, these were the steps that led to a law of nature: 1. Reproducible observations (the sun rises in the east) 2. A hypothesis advanced by Ptolemy and then a better one by Copernicus 3. Experimental data gathered by Galileo in support of the Copernican hypothesis and eventual acceptance of the hypothesis as a theory 4. The statement by Newton of a universal law based on the theory Variations on the scientific method serve us well today as we pursue an urgent search for cures of diseases. An example follows. The Scientific Method in Action The Pacific Yew The bark of this tree is a source of an anticancer drug known as Taxol. FIGURE P-5 The healing power of plants and plant extracts has been known for thousands of years. For example, ancient Sumerians and Egyptians used willow leaves to relieve the pain of arthritis. We now know that extracts of the common willow contain a drug very closely related to aspirin. This is the observation that starts us on our journey to new drugs. An obvious hypothesis comes from this observation, namely, that there are many other useful drugs among the plants and soils of the world. We should be able to find them. There are several recent discoveries that support this hypothesis. For example, the rosy periwinkle is a common tropical plant not too different from thousands of other tropical plants except that this one saves lives. The innocent-looking plant contains a powerful chemical called vincristine, which can cure childhood leukemia. Another relatively new drug called Taxol has been extracted from the Pacific yew tree. (See Figure P-5.) Taxol is effective in treating ovarian cancer and possibly breast cancer. Others include cyclosporine, isolated from a fungus in 1957, which made organ transplants possible, and digoxin, isolated from the foxglove plant, used for treatment of heart failure. In fact, many of the best-selling medicines in the United States originated from plants and other natural sources. Besides those mentioned, other drugs treat conditions such as high blood pressure, cancer, glaucoma, and malaria. The search for effective drugs from natural sources and newly synthesized compounds is very active today. These chemicals are screened for potential anticancer, antiarthritic, and anti-AIDS activity. Since the greatest variety of plants, molds, and fungi are found in tropical forests, these species are receiving the most attention. The introduction of a new medicine from a plant involves the following steps. 1. Collection of materials. “Chemical prospectors” scour the backwoods of the United States and the tropical forests such as those in Costa Rica, collecting and labeling samples of leaves, barks, and roots. Soil samples containing fungi and molds are also collected and carefully labeled. 2. Testing of activity. Scientists at several large chemical and pharmaceutical companies make extracts of the sample in the laboratory. These extracts are run through a series of chemical tests to determine whether there is any antidisease activity among the chemicals in the extract. New methods such as high-throughput-screening (HTS) allow certain chemical companies to screen thousands of chemicals in a single day. If there is antidisease activity, it is considered a “hit” and the extract is taken to the next step. 3. Isolation and identification of the active ingredient. The next painstaking task is to separate the one chemical that has the desired activity from among the “soup” of chemicals present. Once that’s done, the particular structure of the active chemical must be determined. A hypothesis is then advanced about what part of the structure is important and how the chemical works. The hypothesis is tested by attempting to make other more effective drugs (or ones with fewer side effects) based on the chemical’s structure. It is then determined whether the chemical or a modified version of it is worth further testing. MALO_c00_002-013hr.qxd 9-09-2008 13:41 Page 13 C The Scientific Method 4. Testing on animals. If the chemical is considered promising, it is now ready to be tested on animals. This is usually done in government and university labs under strictly controlled conditions. Scientists study toxicity, side effects, and the chemical’s activity against the particular disease for which it is being tested. If, after careful study, the chemical is considered both effective and safe, it is ready for the next step. 5. Testing on humans. The final step is the careful testing on humans in a series of clinical trials carefully monitored by agencies such as the FDA. Effectiveness, dosage, and long-term side effects are carefully recorded and evaluated. All told, it currently takes from 10 to 15 years for a new drug to make it all the way from research and development to market. If a chemical with the desired activity is randomly discovered, only about one in 1000 may actually find its way into general use. Still, the process works. Many chemicals active against cancer and even AIDS (one has been isolated from the mulberry tree) are now in the pipeline for testing. There is some urgency in all of this. Not only are we anxious to cure specific diseases, but the tropical forests that contain the most diverse plants are disappearing at an alarming rate. In any case, nature is certainly our most important chemical laboratory. At this time, most of the drugs that originated from synthetic or natural sources are considered cases of “serendipity.” We are now moving more toward the concept of “rational drug design.” Here, the goal is to identify the active sites on the molecules of diseases such as viruses, tumors, or bacteria. The next step is to deliberately synthesize a drug that attaches to that active site and either destroys or otherwise alters the disease molecules. This sounds easy, but it is not. It requires that we know more about the structure and geometry of these disease molecules. We can then advance hypotheses as to how designed molecules would interact. This is the direction in which pharmaceutical chemists are heading, however. The scientific method has produced cures for many diseases that have plagued the human race for thousands of years. Eventually, it may lead to a cure or vaccine for AIDS. Our modern scientific methods also produce materials for space travel, all sorts of plastics and synthetic fibers, microchips for computers, and processes for genetic engineering. Just a century ago, everything was made out of stone, wood, glass, metal, or natural fibers (wool, cotton, and silk). Our modern society could hardly function on those materials alone. 13 MALO_c01_014-049hr.qxd 12-09-2008 12:40 Page 14 C H A P T E R 1 Measurements in Chemistry T o help fly and land this large aircraft safely, a huge number of dials and gauges are displayed in the cockpit. Ground speed, temperature, cabin pressure, altitude, and location are just a few of the measurements that must be continually available to the experienced pilot. To a large degree, the study of nature in general and chemistry in particular is based on observations. But there is much more. We require reproducible, quantitative measurements. How measurements in chemistry are expressed and manipulated are the subjects of this chapter. MALO_c01_014-049hr.qxd 9-09-2008 13:42 Page 15 PA R T A THE NUMBERS USED IN CHEMISTRY 1-1 The Numerical Value of a Measurement 1-2 Significant Figures and Mathematical Operations MAKING IT REAL Ted Williams and Significant Figures 1-3 Expressing Large and Small Numbers: Scientific Notation PA R T B THE MEASUREMENTS USED IN CHEMISTRY 1-4 Measurement of Mass, Length, and Volume MAKING IT REAL Worlds from the Small to the Distant—Picometers to Terameters 1-5 Conversion of Units by the Factor-Label Method 1-6 Measurement of Temperature S E T T I N G T H E S TA G E Before we were even aware of our own existence, we were being subjected to measurements. Within the first few minutes of our lives, we were placed on a scale and against a tape measure to provide our first weight and length. Years later, as adults, we now find ourselves immersed in a complex world that measures just about anything that lends itself to being measured. For example, it is hard to conceive of being able to operate a modern automobile without a speedometer as well as temperature and fuel gauges. The more expensive the car, the more measurements that are reported by more gauges and dials. If one pays enough, a global positioning satellite will even measure where you are and tell you how to get where you are going. Pilots, carpenters, artists, teachers, and most other professionals and skilled workers are usually involved in some type of measurement. So chemists are hardly unique in their reliance on measurements. Chemistry is a science that requires us to deal with all the stuff that we see around us. This stuff, which we call matter, is subject to the laws of nature. Many of these laws originate from reproducible quantitative measurements. Measurements naturally contain numbers. The quality, meaning, magnitude, and manipulation of the numbers we use in chemistry form the beginning point of our study. Our journey into the actual concepts of chemistry begins in the next chapter. If you are not in at least fair physical shape, playing a strenuous sport is not fun—it is exhausting and probably frustrating. Likewise, doing chemistry can be frustrating if you are not in at least fair mathematical shape. It is likely that most students need at least a bit of a mathematical workout to get into shape. For some, a simple review will do, and that is provided in the text. At appropriate points in this chapter, you will also be referred to a specific appendix in the back of the book for more extensive review. Review appendixes include basic arithmetical operations (Appendix A), basic algebra operations (Appendix B), and scientific notation (Appendix C). Also, Appendix E can aid you in the use of calculators for the mathematical operations found in the text. If you are worried about the math, you are not alone. Just remember that this text was written with your concerns in mind. Measurements consist of two parts—a number and a specific unit. We will discuss these two parts separately. In Part A, we will address questions about the numerical quantity of a measurement. The units that are used in the measurement are then discussed in Part B. 15 MALO_c01_014-049hr.qxd 16 12-09-2008 CHAPTER 1 12:41 Page 16 Measurements in Chemistry PA R T A THE NUMBERS USED IN CHEMISTRY OBJ ECTIVES SETTI NG A GOAL ■ You will learn how to apply and manipulate measurements to produce scientifically meaningful outcomes. 1-1 (a) Describe the difference between accuracy and precision. (b) Determine the number of significant figures in a measurement. 1-2 Perform arithmetic operations, rounding the answer to the appropriate number of significant figures. 1-3 (a) Write very large or small measurements in scientific notation. (b) Perform arithmetic operations involving scientific notation. 䉴 OBJECTIVES FOR SECTION 1-1 (a) Describe the difference between accuracy and precision. (b) Determine the number of significant figures in a measurement. 1-1 T H E N U M E R I C A L VA L U E O F A M E A S U R E M E N T A H E A D ! Much of science is based on numbers. How reliable are the numbers and what do they really tell us? In this section, we will evaluate the quality and reliability of the numbers that are part of a measurement. ■ LOOKING 1-1.1 The Qualities of a Number We will start this chapter with a formal definition of a measurement. A measurement determines the quantity, dimensions, or extent of something, usually in comparison to a specific unit. A unit is a definite quantity adopted as a standard of measurement. Thus, a measurement (e.g., 1.23 meters) consists of two parts: a numerical quantity (1.23) followed by a specific unit (meters). First let’s consider the numerical value of a measurement. Assume that the evening news informs us that 12,000 people gathered for a concert. Did they mean exactly 12,000? Not really—actually, it was just an estimate. Two other experts may have estimated the same crowd at 13,000 and 11,000, respectively. This means that the original estimate had an uncertainty of ⫾1000. Thus only the 1 and 2 are considered significant in this estimate. The three zeros simply tell us the magnitude of the number. In a measurement, a significant figure is a digit that is either reliably known or closely estimated. In the number 12,000, we can assume the 1 is reliable and reproducible from any number of estimates, but the 2 is estimated. The zeros are not significant since they actually have no specific numerical meaning. Thus, in our example, there are two significant figures: the 1 and the 2. The number of significant figures or digits in a measurement is simply the number of measured digits and refers to the precision of the measurement. Precision relates to the degree of reproducibility or uncertainty of the measurement. Indeed, all measured values have an uncertainty that is expressed in the last significant figure to the right. Now assume the same crowd at the concert is seated in the bleachers of a stadium instead of milling about. In this case, a more precise estimate is possible since the exact capacity of the stadium is known. The crowd can now be estimated at between 12,400 and 12,600, or an average of 12,500. This is a measurement with three significant figures. The 1 and 2 are now reliable, but the third significant figure, the 5, is estimated. The extra significant figure means that the uncertainty is now reduced to ⫾100. The more significant figures in a measurement, the more precise it is. If the crowd went through a turnstile before entering the stadium, an even more precise number could be given. Notice that the significant figure farthest to the right in a measurement is estimated. MALO_c01_014-049hr.qxd 9-09-2008 13:42 Page 17 1-1 The Numerical Value of a Measurement 17 Participants in the sport of riflery (target shooting) are judged on two points: how close the bullet holes are to each other (the pattern) and how close the pattern is to the center of the target known as the bull’s-eye. The precision of the contestant’s shooting is measured by the tightness of the pattern. How close the pattern is to the High accuracy Low accuracy Low accuracy bull’s-eye is a measure of the shooter’s High precision Low precision High precision accuracy. Accuracy in a measurement refers to how close the measurement is to the true value. Usually, the more precise the meas- F I G U R E 1 - 1 Precision and urement, the more accurate it is—but not always. In our example, if a certain com- Accuracy High precision does not petitor has a faulty sight on the rifle, the shots may be close together (precise) but necessarily mean high accuracy. off center (inaccurate). (See Figure 1-1.) Accuracy in measurements depends on how carefully the instrument of measurement has been calibrated (compared to a reliable standard). For example, what if we attempted to measure length with a plastic ruler that became warped after being left in the hot sun? We obviously would not obtain accurate readings. We would need to recalibrate the ruler by comparing its length divisions to a reliable standard. 1-1.2 Zero as a Significant Figure It would be easy to determine the number of significant figures in a measurement if it were not for the number zero. Unfortunately, zero serves two functions: as a reliable or estimated digit, or simply as a marker to locate the decimal point (such as the three zeros in the estimated crowd of 12,000 people). Since the zeros look alike in both cases, it is important for us to know whether a zero is significant or is there simply to locate the decimal point. The following rules can be used to tell us about zero. Digits that are underlined are significant. 1. When a zero is between other nonzero digits, it is significant. 709 has three significant figures. Zeros between two nonzero digits are always siginificant. 2. Zeros to the right of a nonzero digit and to the right of the decimal point are significant. 8.0 has two significant figures, just as 7.9 and 8.1 do. 7.900 has four significant figures. There is no value difference between 8.0 and just 8. Why, then, is the zero added? Quite simply because it is an estimated digit and should be included. 3. Zeros to the left of the first nonzero digit are not significant. 0.0078 and 0.45 both have two significant figures; 0.04060 has four significant figures. In this case, the zeros to the left of the digit are simply showing the decimal place and are not measured or estimated digits. Therefore, they are not significant. 4. Zeros to the left of an implied decimal point may or may not be significant. In most cases, they are not. The crowd of 12,000 has two significant figures, as does 6600. Just as in the above case, the zeros to the left are decimal place holders, not actual measurements. What if the zero in a number such as 890 is actually an estimated digit and thus significant? This is a tough question. Some texts use a line over the zero to indicate that it is significant (e.g., 890), and others simply place a decimal point after the zero (e.g., 890.). As we will see in Section 1-3, there is a solution to this dilemma. In most problems used in this text, measurements are expressed to three significant figures. Therefore, in calculations where other numbers have three significant figures, we will assume that numbers such as 890 also have three significant figures. MALO_c01_014-049hr.qxd 18 9-09-2008 CHAPTER 1 EXAMPLE 13:42 Page 18 Measurements in Chemistry 1-1 Evaluating Zero as a Significant Figure How many significant figures are in the following measurements? What is the uncertainty in each of the measurements? (a) 1508 cm (b) 300.0 ft (c) 20.003 lb (d) 0.00705 gal PROCEDURE To determine the number of significant figures, refer to the rules regarding zero that were listed. Since these numbers all involve measurements, the last significant figure to the right is estimated. This digit indicates the uncertainty of the measurement. SOLUTION (a) The zero between the two nonzero digits is significant. There are four significant figures. The uncertainty is in the last digit to the right, so is 1 cm. (b) The zero to the right of the decimal point is significant because it is displayed. Therefore, the other two zeros are also significant because they lie between significant figures. There are four significant figures. The uncertainty is in the last zero to the right, so is 0.1 ft. (c) All the zeros are between nonzero digits, so they are all significant. There are five significant figures. The uncertainty is in the last digit to the right, so is 0.001 lb. (d) The three zeros to the left of the first nonzero digit are not significant. The zero between the two nonzero digits is significant. Thus, there are three significant figures. The uncertainty is in the last digit to the right, so is 0.00001 gal. A N A LY S I S Be certain not to confuse the concept of “significant” with the idea of “important.” In the measurement 0.00705 gallons, the two zeros immediately following the decimal are most assuredly important to the value of the number. Without them, the value changes. But significant refers to a measurement. In that particular example, the measurement doesn’t start until you reach the 7. Therefore, the zeros, while necessary, are not significant. SYNTHESIS The more significant figures there are in a measurement, the more precise it is. The closest the Earth and sun ever get to one another is 147,098,000 km. The uncertainty is 1000 km. The distance between New York and Philadelphia is 127 km, known with a precision to the nearest kilometer. One would assume that knowing a distance to a kilometer would be more precise than to the nearest 1000 kilometers. And yet, because the measured distance to the sun has six significant figures in it, it is 1000 times more precise than the measured driving distance between the two cities. Which of the four measurements in the problem is the most precise? 20.003 lb. It has more significant figures than any of the others. ASSESSING THE OBJECTIVES FOR SECTION 1-1 1 - 1 ( a ) K N O W L E D G E : Students in different class sections attempted to measure the mass of a 100.0-gram object. Describe the series of measurements as precise, precise and accurate, or neither. (a) class 1: 94.2 g, 93.8 g, 94.4 g, 94.0 g (b) class 2: 94.3 g, 89.7 g, 102.4 g, 97.8 g (c) class 3: 100.2 g, 100.0 g, 99.8 g, 99.8 g EXERCISE You are determining the boiling point of an unknown compound in degrees Celsius. On three successive attempts, you record 145.5°C, 145.8°C, and 146.0°C. Are your data precise? Are your data accurate? Is there extra information needed to make either of those claims? EXERCISE 1-1(b) SYNTHESIS: E X E R C I S E 1 - 1 ( c ) A N A LY S I S : in the following measurements: (a) 45.00 oz (b) 0.045 lbs Determine the number of significant figures (c) 45000 s (d) 0.450 in. 1 - 1 ( d ) S Y N T H E S I S : Two models of analytical balance are available for purchase. The first measures to 0.01 gram. The second is more EXERCISE MALO_c01_014-049hr.qxd 9-09-2008 13:42 Page 19 1-2 Significant Figures and Mathematical Operations 19 expensive, but measures to 0.0001 gram. How many significant figures will each give when measuring the mass of an object of about 25 grams? What considerations would you include in determining which model to buy? (Throughout the text, answers to all Assessing the Objectives exercises can be found at the end of each chapter.) For additional practice, work chapter problems 1-1, 1-3, 1-4, and 1-6. 1-2 SIGNIFICANT FIGURES AND M AT H E M AT I C A L O P E R AT I O N S 䉴 OBJECTIVE FOR SECTION 1-2 Perform arithmetic operations, rounding the answer to the appropriate number of significant figures. L O O K I N G A H E A D ! In science we are continually adding, multiplying, or performing other calculations involving various measurements. Often these measurements involve different degrees of precision, so we need to understand how to report the results of such calculations. ■ For under $10 we can own a small calculator that can almost instantly carry out any calculation we may encounter in general chemistry. This device is truly phenomenal, especially to older scientists, who years ago had to carry out these calculations using a slide rule. (This was a simple but effective device that performed many of the calculations found on an electronic calculator but not as quickly or as precisely.) The use of the calculator does have one serious drawback, however. It does not necessarily report the answer to a calculation involving measurements to the proper precision or number of significant figures. For example, 7.8 divided by 2.3 reads 3.3913043 on a standard eight-digit display. However, if the numbers represented measurements known to only two significant figures (e.g., 7.8 lb and 2.3 qt), then the calculator has created the illusion that these numbers were known to a much greater precision. Since the calculator does not express the answer to the calculation with the proper precision, we must know how to prune the answer so that the reported value is honest and appropriate. 1-2.1 Rules for Addition and Subtraction and Rounding Off There are two sets of rules for properly expressing the result of a mathematical operation: one applies to addition and subtraction and the other applies to multiplication and division. We will discuss the rule for addition and subtraction first. When numbers are added or subtracted, the answer is expressed to the same number of decimal places as the measurement with the fewest decimal places. Or, in other words, the summation must have the same degree of uncertainty as the measurement with the most uncertainty (e.g., 100 has more uncertainty than 10 and 0.1 more than 0.01). This is illustrated by the following summation. 10.6871 1.42 12.1071 = (four decimal places, or uncertainty of ; 0.0001) (two decimal places, or uncertainty of ; 0.01) 12.11(two decimal places, or uncertainty of ; 0.01) Notice that 1.42 and the answer have the same uncertainty. Therefore, expressing the 71 in the summation has no meaning and cannot be included except for rounding-off purposes. The calculator does not give the answer to the proper number of decimal places. The rules for rounding off a number are as follows (the examples are all to be rounded off to three significant figures). 1. If the digit to be dropped is less than 5, simply drop that digit (e.g., 12.44 is rounded down to 12.4). The calculator does not give the answer to the proper number of decimal places or significant figures. MALO_c01_014-049hr.qxd 20 9-09-2008 CHAPTER 1 13:42 Page 20 Measurements in Chemistry 2. If the digit to be dropped is 5 or greater, increase the precedin