Preview Chemistry The Central Science, 3rd Edition by Theodore L. Brown, H. Eugene LeMay, Bruce E. Bursten, Catherine Murphy, Patrick Woodward, Steven Langford, Dalius Sagatys, Adrian Georg (2013)

Preview Chemistry The Central Science, 3rd Edition by Theodore L. Brown, H. Eugene LeMay, Bruce E. Bursten, Catherine Murphy, Patrick Woodward, Steven Langford, Dalius Sagatys, Adrian Georg (2013) Preview Chemistry The Central Science, 3rd Edition by Theodore L. Brown, H. Eugene LeMay, Bruce E. Bursten, Catherine Murphy, Patrick Woodward, Steven Langford, Dalius Sagatys, Adrian Georg (2013) Preview Chemistry The Central Science, 3rd Edition by Theodore L. Brown, H. Eugene LeMay, Bruce E. Bursten, Catherine Murphy, Patrick Woodward, Steven Langford, Dalius Sagatys, Adrian Georg (2013) Preview Chemistry The Central Science, 3rd Edition by Theodore L. Brown, H. Eugene LeMay, Bruce E. Bursten, Catherine Murphy, Patrick Woodward, Steven Langford, Dalius Sagatys, Adrian Georg (2013)

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Visit www.pearson.com.au/masteringchemistry for a full suite of learning resources including your Pearson eText, tutorials with guided hints and instant, personalised feedback, and interactive versions of the text end-of-chapter questions T H E C E N T R A L S C I E N C E S C I E N C E Remove the barriers to learning, one concept at a time, with MasteringChemistry Used by over a million science students, the Mastering platform is the most effective and widely used online tutorial, homework and assessment system for the sciences C E N T R A L MasteringChemistry CHEMISTRY B R O W N • L E M A Y • B U R S T E N • M U R P H Y RD W O O D WA R D • L A N G F O R D • S A G AT Y S • G E O R G E E D I T I O N BROWN • LEMAY BURSTEN • MURPHY WOODWARD • LANGFORD SAGATYS • GEORGE RD E D I T I O N Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e Brown full cover.indd 26/06/13 2:04 PM C HE MIS T RY R D E D I T I O N Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e To our families for their love, support and understanding and to our students, whose enthusiasm and curiosity have inspired us to undertake this project Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e C HE MIS T RY T H E C E N T R A L S C I E N C E B R O W N • L E M A Y • B U R S T E N • M U R P H Y W O O D WA R D • L A N G F O R D • S A G AT Y S • G E O R G E R D E D I T I O N Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 Pearson Australia Unit 4, Level 14 Aquatic Drive Frenchs Forest NSW 2086 www.pearson.com.au Authorised adaptation from the United States edition entitled Chemistry: The Central Science, 12th edition, ISBN 01321696727 by Brown, Theodore L.; LeMay, H Eugene Jr; Bursten, Bruce E.; Murphy, Catherine J.; Woodward, Patrick M., published by Pearson Education, Inc., copyright © 2012 Third adaptation edition published by Pearson Australia Group Pty Ltd, Copyright © 2014 The Copyright Act 1968 of Australia allows a maximum of one chapter or 10% of this book, whichever is the greater, to be copied by any educational institution for its educational purposes provided that that educational institution (or the body that administers it) has given a remuneration notice to Copyright Agency Limited (CAL) under the Act For details of the CAL licence for educational institutions contact: Copyright Agency Limited, telephone: (02) 9394 7600, email: info@copyright.com.au All rights reserved Except under the conditions described in the Copyright Act 1968 of Australia and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner Senior Acquisitions Editor: Mandy Sheppard Manager—Product Development: Michael Stone Senior Project Editor: Katie Millar Development Editors: Catherine du Peloux Menage, David Chelton Media Content Developer, MasteringChemistry: Adam Catarius Editorial Coordinator: Camille Layt Production Coordinator: Julie McArthur Copy Editor: Jennifer Coombs Proofreader: Judi Walters Copyright and Pictures Editor: Lisa Woodland Indexer: Mary Coe Cover design by Natalie Bowra Typeset by Midland Typesetters, Australia Printed in China 18 17 16 15 14 National Library of Australia Cataloguing-in-Publication Data Title: Chemistry: the central science/Theodore L Brown [et al.] Edition: 3rd ed ISBN: ISBN: 9781442554603 (pbk) 9781442559462 (Vital Source) Notes: Includes index Subjects: Chemistry—Textbooks Other Authors/Contributors: Brown, Theodore L Dewey Number: 540 Every effort has been made to trace and acknowledge copyright However, should any infringement have occurred, the publishers tender their apologies and invite copyright owners to contact them Due to copyright restrictions, we may have been unable to include material from the print edition of the book in this digital edition, although every effort has been made to minimise instances of missing content Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e brief contents 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Introduction: Matter and Measurement Atoms, Molecules and Ions 28 Stoichiometry: Calculations with Chemical Formulae and Equations 66 Reactions in Aqueous Solutions 102 Nuclear Chemistry: Changes within the Core of an Atom 142 Electronic Structure of Atoms 178 Periodic Properties of the Elements 220 Basic Concepts of Chemical Bonding 250 Molecular Geometry and Bonding Theories 292 Intermolecular Forces: Gases 336 Intermolecular Forces: Liquids and Solids 376 Properties of Solutions 426 Environmental Chemistry 468 Thermodynamics 500 Chemical Kinetics 564 Chemical Equilibrium 614 Acid–Base Equilibria 654 Additional Aspects of Aqueous Equilibria 706 Electrochemistry 752 Chemistry of the Non-Metals 802 Chemistry of the Transition Metals 850 The Chemistry of Organic Compounds 890 Stereochemistry 926 Chemistry of Alkenes and Alkynes 952 Alcohols, Haloalkanes and Ethers 994 Aldehydes, Ketones and Carbohydrates 1034 Carboxylic Acids and their Derivatives 1076 Benzene and its Derivatives 1114 Nitrogen-Containing Organic Compounds 1146 Solving Molecular Structure 1198 Appendices A–E Answers Glossary Index 1252 1265 1280 1296 Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e detailed contents Preface Guided tour for students Guided tour for students and educators Guided tour for educators Acknowledgements About the Australian authors About the American authors xxii xxiv xxvi xxviii xxix xxx xxxii 1.1 1.2 1.3 1.4 1.5 Chapter summary and key terms Key skills Key equations Exercises 22 23 23 23 23 chapter chapter Introduction: Matter and measurement STRATEGIES IN CHEMISTRY The features of this book Atoms, molecules and ions 28 2.1 Atomic theory of matter 30 2.2 The discovery of atomic structure Cathode rays and electrons Radioactivity The nuclear atom 31 31 32 33 2.3 The modern view of atomic structure 34 A CLOSER LOOK Basic forces Atomic numbers, mass numbers and isotopes 36 Atomic mass The atomic mass scale Average atomic masses 37 37 38 A CLOSER LOOK The mass spectrometer 39 2.5 The periodic table 39 2.6 Molecules and molecular compounds Molecules and chemical formulae Molecular and empirical formulae Picturing molecules 42 42 42 43 2.7 Ions and ionic compounds Predicting ionic charges Ionic compounds 44 45 46 The study of chemistry The atomic and molecular perspective of chemistry Why study chemistry? Classifications of matter States of matter Composition of matter 5 Properties of matter Physical and chemical changes Separation of mixtures 9 Units of measurement SI units A CLOSER LOOK The scientific method Derived SI units 10 10 11 14 Uncertainty in measurement 16 MY WORLD OF CHEMISTRY Chemistry in the news Precision and accuracy Significant figures Significant figures in calculations 16 18 18 20 STRATEGIES IN CHEMISTRY The importance of practice and estimating answers 21 2.4 36 Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e detailed contents MY WORLD OF CHEMISTRY Elements required by living organisms 2.8 2.9 3.6 48 Naming inorganic compounds Names and formulae of ionic compounds Names and formulae of acids Names and formulae of binary molecular compounds 48 49 54 Some simple organic compounds Alkanes Some derivatives of alkanes 56 56 56 Chapter summary and key terms Key skills Exercises 55 3.7 Quantitative information from balanced chemical equations 87 Limiting reactants Theoretical yields 90 92 Chapter summary and key terms Key skills Key equations Exercises 94 95 95 96 chapter Reactions in aqueous solutions 102 58 59 59 chapter Stoichiometry: Calculations with chemical formulae and equations 66 3.1 Chemical equations Balancing equations Indicating the states of reactants and products 68 68 70 3.2 Some simple patterns of chemical reactivity Combination and decomposition reactions Combustion reactions 71 71 74 Formula mass Formula and molecular masses Percentage composition from formulae 75 75 76 STRATEGIES IN CHEMISTRY Problem solving 76 Avogadro’s number and the mole Molar mass 77 78 3.3 3.4 MY WORLD OF CHEMISTRY Glucose monitoring Interconverting masses and moles Interconverting masses and numbers of particles 3.5 Empirical formulae from analyses Molecular formulae from empirical formulae Combustion analysis 4.1 General properties of aqueous solutions Electrolytic properties Ionic compounds in water Molecular compounds in water Strong and weak electrolytes 104 104 105 106 106 4.2 Precipitation reactions Solubility guidelines for ionic compounds Exchange (metathesis) reactions Ionic equations 107 108 109 110 4.3 Acids, bases and neutralisation reactions Acids Bases Strong and weak acids and bases Neutralisation reactions and salts Neutralisation reactions with gas formation 112 112 112 113 114 116 MY WORLD OF CHEMISTRY Antacids 117 Oxidation–reduction reactions Oxidation and reduction Oxidation numbers Oxidation of metals by acids and salts The activity series 118 118 119 120 122 A CLOSER LOOK The aura of gold 124 Concentrations of solutions Molarity Expressing the concentration of an electrolyte Interconverting molarity, moles and volume 125 125 126 127 4.4 80 81 82 83 85 85 4.5 Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e vii viii Chemistry: the central science Dilution MY WORLD OF CHEMISTRY Drinking too much water can kill you 4.6 Solution stoichiometry and chemical analysis Titrations Chapter summary and key terms Key skills Key equations Exercises A CLOSER LOOK The dawning of the nuclear age Nuclear waste 166 166 5.8 Nuclear power: Fusion 167 5.9 Radiation in the environment and living systems Radiation doses Radon 168 169 170 128 128 130 131 135 136 136 136 chapter Nuclear chemistry: Changes within the core of an atom 142 MY WORLD OF CHEMISTRY Radiation therapy 170 Chapter summary and key terms Key skills Key equations Exercises chapter Electronic structure of atoms Radioactivity Nuclear equations Types of radioactive decay 144 144 145 Patterns of nuclear stability Neutron-to-proton ratio Radioactive series Further observations 147 147 149 149 5.3 Nuclear transmutations Accelerating charged particles Reactions involving neutrons Transuranium elements 151 151 152 152 5.4 Rates of radioactive decay Radiometric dating Calculations based on half-life 152 154 155 5.5 Detection of radioactivity Radiotracers 157 159 5.6 Energy changes in nuclear reactions 159 MY WORLD OF CHEMISTRY Medical applications of radiotracers Nuclear binding energies 160 162 Nuclear power: Fission Nuclear reactors 163 164 5.1 5.2 5.7 172 173 173 174 178 6.1 The wave nature of light 180 6.2 Quantised energy and photons Hot objects and the quantisation of energy The photoelectric effect and photons 183 183 184 6.3 Line spectra and the Bohr model Line spectra Bohr’s model The energy states of the hydrogen atom Limitations of the Bohr model 185 186 187 187 189 6.4 The wave behaviour of matter 189 MY WORLD OF CHEMISTRY Australian Synchrotron The uncertainty principle 191 191 6.5 Quantum mechanics and atomic orbitals 192 Orbitals and quantum numbers 194 6.6 Representations of orbitals The s orbitals The p orbitals The d and f orbitals 196 196 198 199 A CLOSER LOOK Probability density and radial probability functions 200 Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e detailed contents 6.7 6.8 6.9 Many-electron atoms 200 Orbitals and their energies 200 Electron spin and the Pauli exclusion principle 201 Electron configurations 202 chapter Hund’s rule 203 Electron configurations 205 Basic concepts of chemical bonding Transition metals 206 The lanthanides and actinides 206 Chapter summary and key terms Key skills Key equation Exercises 243 244 244 244 250 Electron configurations and the periodic table 207 Anomalous electron configurations 210 Chapter summary and key terms Key skills Key equations Exercises 212 213 213 213 chapter 8.1 Chemical bonds, Lewis symbols and the octet rule Lewis symbols The octet rule 252 252 252 Ionic bonding Energetics of ionic bond formation Electron configurations of ions of the main-group elements Transition metal ions Polyatomic ions 253 254 8.3 Covalent bonding Lewis structures Multiple bonds 258 258 260 8.4 Bond polarity and electronegativity Electronegativity Electronegativity and bond polarity Dipole moments Differentiating ionic and covalent bonding 260 261 262 263 265 8.5 Drawing Lewis structures Formal charge 267 269 A CLOSER LOOK Oxidation numbers, formal charges and actual partial charges 272 8.2 Periodic properties of the elements 220 256 257 258 7.1 Development of the periodic table 222 7.2 Effective nuclear charge 223 A CLOSER LOOK Effective nuclear charge 225 Sizes of atoms and ions Periodic trends in atomic radii Periodic trends in ionic radii 225 227 228 Ionisation energy 230 Variations in successive ionisation energies 231 Periodic trends in first ionisation energies 232 Electron configurations of ions 234 8.6 Resonance structures 272 7.5 Electron affinities 235 8.7 7.6 Metals, non-metals and metalloids Metals 236 237 MY WORLD OF CHEMISTRY Ion movement powers electronics Non-metals Metalloids Exceptions to the octet rule Odd number of electrons Less than an octet of valence electrons More than an octet of valence electrons 274 275 275 276 238 241 242 8.8 Strengths of covalent bonds Bond enthalpies and the enthalpies of reactions 277 7.3 7.4 278 Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e ix *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 43 SECTION 2.6 Molecules and Molecular Compounds formulae.) Chemical formulae that give only the relative number of atoms of each type in a molecule are called empirical formulae or simplest formulae The subscripts in an empirical formula are always the smallest possible whole-number ratios The molecular formula for hydrogen peroxide is H2O2, for example, whereas its empirical formula is HO The molecular formula for ethylene is C2H4, and its empirical formula is CH2 For many substances, the molecular formula and the empirical formula are identical, as in the case for water, H2O Molecular formulae provide more information about molecules than empirical formulae Whenever we know the molecular formula of a compound, we can determine its empirical formula The converse is not true, however; if we know the empirical formula of a substance, we can’t determine its molecular formula unless we have more information So why chemists bother with empirical formulae? Once the empirical formula is known, additional experiments can give the information needed to convert the empirical formula to the molecular one In addition, there are substances, such as the most common forms of elemental carbon, that don’t exist as isolated molecules For these substances, we must rely on empirical formulae Thus all the common forms of elemental carbon are represented by the element’s chemical symbol C, which is the empirical formula for all the forms SAMPLE EXERCISE 2.6 Hydrogen, H2 Oxygen, O2 Water, H2O Hydrogen peroxide, H2O2 Carbon monoxide, CO Carbon dioxide, CO2 Methane, CH4 Ethene, C2H4 43 Relating empirical and molecular formulae Write the empirical formulae for the following molecules: (a) glucose, a substance also known as either blood sugar or dextrose, whose molecular formula is C6H12O6; (b) nitrous oxide, a substance used as an anaesthetic and commonly called laughing gas, whose molecular formula is N2O SOLUTION (a) The subscripts of an empirical formula are the smallest whole-number ratios The smallest ratios are obtained by dividing each subscript by the largest common factor, in this case The resultant empirical formula for glucose is CH2O (b) Because the subscripts in N2O are already the lowest integral numbers, the empirical formula for nitrous oxide is the same as its molecular formula, N2O į FIGURE 2.14 Molecular models Notice how the chemical formulae of these simple molecules correspond to their compositions PRACTICE EXERCISE Give the empirical formula for the substance called diborane, whose molecular formula is B2H6 Answer: BH3 (See also Exercises 2.28–2.30.) Picturing Molecules The molecular formula of a substance summarises the composition of the substance but does not show how the atoms come together to form the molecule The structural formula of a substance shows which atoms are attached to which within the molecule For example, the structural formulae for water, hydrogen peroxide and methane (CH4) can be written as follows: H H O H O H Water O H Hydrogen peroxide H C H H Methane The atoms are represented by their chemical symbols, and lines are used to represent the bonds that hold the atoms together A structural formula usually does not depict the actual geometry of the molecule, that is, the actual angles between the lines joining the nuclei A structural formula can be written as a perspective drawing, however, to give some sense of three-dimensional shape, as shown in Ĭ FIGURE 2.15 Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 44 44 Atoms, Molecules and Ions CHAPTER FIGURE IT OUT What advantage does a ball-andstick model have over a spacefilling model? CH Molecular formula H H C H H Scientists also rely on various models to help visualise molecules Ball-andstick models show atoms as spheres and bonds as sticks This type of model has the advantage of accurately representing the angles at which the atoms are attached to one another within the molecule (Figure 2.15) All atoms may be represented by balls of the same size, or the relative sizes of the balls may reflect the relative sizes of the atoms Sometimes the chemical symbols of the elements are superimposed on the balls, but often the atoms are identified simply by colour A space-filling model depicts what the molecule would look like if the atoms were scaled up in size (Figure 2.15) These models show the relative sizes of the atoms, but the angles between atoms, which help define their molecular geometry, are often more difficult to see than in ball-and-stick models As in ball-andstick models, the identities of the atoms are indicated by their colours, but they may also be labelled with the element’s symbol Structural formula Dashed wedge is bond behind page H H C Solid line is bond in plane of page CONCEPT CHECK The structural formula for the substance ethane is shown here: H Wedge is bond out of page Perspective drawing H H H H C C H H H a What is the molecular formula for ethane? b What is its empirical formula? c Which kind of molecular model would most clearly show the angles between atoms? 2.7 | IONS AND IONIC COMPOUNDS Ball-and-stick model The nucleus of an atom is unchanged by chemical processes, but atoms can readily gain or lose electrons If electrons are removed from or added to a neutral atom, a charged particle called an ion is formed An ion with a positive charge is called a cation (pronounced CAT-ion); a negatively charged ion is called an anion (AN-ion) To see how ions form, consider the sodium atom, which has 11 protons and 11 electrons This atom may lose one electron The resulting cation has 11 protons and 10 electrons, which means it has a net charge of 1+ 11e᎐ 11pϩ 11pϩ Loses an electron Space-filling model į FIGURE 2.15 Different representations of the methane (CH4) molecule Structural formulae, perspective drawings, ball-and-stick models and spacefilling models correspond to the molecular formula, and each helps us visualise the ways atoms are attached to each other 10e᎐ Naϩ ion Na atom The net charge on an ion is represented by a superscript; the superscripts +, 2+ and 3+ for instance, mean a net charge resulting from the loss of one, two and three electrons, respectively The superscripts -, 2- and 3- represent net charges resulting from the gain of one, two and three electrons, respectively Chlorine, with 17 protons and 17 electrons, for example, can gain an electron in chemical reactions, producing the Cl- ion: 17pϩ 17e᎐ 17pϩ 18e᎐ Gains an electron Cl atom Cl᎐ ion Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 45 SECTION 2.7 Ions and Ionic Compounds In general, metal atoms tend to lose electrons to form cations, whereas non-metal atoms tend to gain electrons to form anions SAMPLE EXERCISE 2.7 Writing chemical symbols for ions Give the chemical symbol, including mass number, for each of the following ions: (a) the ion with 22 protons, 26 neutrons and 19 electrons; (b) the ion of sulfur that has 16 neutrons and 18 electrons SOLUTION (a) The number of protons (22) is the atomic number of the element, which means this element is titanium (Ti) The mass number of this isotope is 22 + 26 = 48 (the sum of the protons and neutrons) Because the ion has three more protons than electrons, it has a net charge of 3+ Thus the symbol for the ion is 48Ti3+ (b) By referring to a periodic table or a table of elements, we see that sulfur (S) has an atomic number of 16 Thus, each atom or ion of sulfur must contain 16 protons We are told that the ion also has 16 neutrons, meaning the mass number of the ion is 16 + 16 = 32 Because the ion has 16 protons and 18 electrons, its net charge is 2- Thus the symbol for the ion is 32S2- In general, we will focus on the net charges of ions and ignore their mass numbers PRACTICE EXERCISE How many protons and electrons does the Se2- ion possess? Answer: 34 protons and 36 electrons (See also Exercises 2.36, 2.37.) In addition to simple ions, such as Na+ and Cl- there are polyatomic ions, such as NH4+ (ammonium ion) and SO42- (sulfate ion) These latter ions consist of atoms joined as in a molecule, but they have a net positive or negative charge We consider further examples of polyatomic ions in Section 2.8 It is important to realise that the chemical properties of ions are very different from the chemical properties of the atoms from which the ions are derived The difference is like the change from Dr Jekyll to Mr Hyde: although a given atom and its ion may be essentially the same (plus or minus a few electrons), the behaviour of the ion is very different from that of the atom Predicting Ionic Charges Many atoms gain or lose electrons so as to end up with the same number of electrons as the noble gas closest to them in the periodic table This is called the octet rule (• Section 8.1, ‘Chemical Bonds, Lewis Symbols and the Octet Rule’) The members of the noble gas family are chemically very non-reactive and form very few compounds We might deduce that this is because their electron arrangements are very stable Nearby elements can obtain these same stable arrangements by losing or gaining electrons For example, loss of one electron from an atom of sodium leaves it with the same number of electrons as the neutral neon atom (atomic number 10) Similarly, when chlorine gains an electron, it ends up with 18, the same number of electrons as in argon (atomic number 18) We will use this simple observation to explain the formation of ions until Chapter 8, where we discuss chemical bonding SAMPLE EXERCISE 2.8 • Find out more on page 253 Predicting the charges of ions Predict the charge expected for the most stable ion of barium and for the most stable ion of oxygen SOLUTION We will assume that these elements form ions that have the same number of electrons as the nearest noble gas atom From the periodic table, we see that barium has atomic number 56 The nearest noble gas is xenon, atomic number 54 Barium can attain a stable arrangement of 54 electrons by losing two of its electrons, forming the Ba2+ cation Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e 45 *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 46 46 CHAPTER Atoms, Molecules and Ions 17 Hϩ HϪ 13 14 Liϩ Ǡ FIGURE 2.16 Charges of some common ions Notice that the steplike line that divides metals from non-metals also separates cations from anions 15 3Ϫ N Transition metals Naϩ Mg2ϩ Kϩ 18 Al3ϩ 16 O 2Ϫ S2Ϫ Ϫ F ClϪ Se2Ϫ BrϪ Ca2ϩ Rbϩ Sr2ϩ Te2Ϫ IϪ N O B L E G A S E S Csϩ Ba2ϩ Oxygen has atomic number The nearest noble gas is neon, atomic number 10 Oxygen can attain this stable electron arrangement by gaining two electrons, thereby forming the O2- anion P R ACTICE EXERCISE Predict the charge expected for the most stable ion of (a) aluminium and (b) fluorine Answer: (a) 3+, and (b) 1(See also Exercises 2.38, 2.39.) The periodic table is very useful for remembering the charges of ions, especially those of the elements on the left and right sides of the table As į FIGURE 2.16 shows, the charges of these ions relate in a simple way to their positions in the table On the left side of the table, for example, the group elements (the alkali metals) form 1+ ions and the group elements (the alkaline earth metals) form 2+ ions On the other side of the table, the group 17 elements (the halogens) form 1- ions (17 - 18 = 1-) and the group 16 elements form 2- ions (16 - 18 = 2-) As we will see later in the text, many of the other groups not lend themselves to such simple rules Ionic Compounds A great deal of chemical activity involves the transfer of electrons from one substance to another, and, as we just saw, ions form when one or more electrons transfer from one neutral atom to another Ĭ FIGURE 2.17 shows that when ele11pϩ 11e᎐ Loses an electron 11pϩ 10e᎐ Naϩ ion Na atom 17pϩ e؊ 17e᎐ 18e᎐ 17pϩ Gains an electron Cl atom Cl᎐ ion (a) (b) (c) į FIGURE 2.17 Formation of an ionic compound (a) The transfer of an electron from a Na atom to a Cl atom leads to the formation of a Naϩ ion and a ClϪ ion (b) Arrangement of these ions in solid sodium chloride, NaCl (c) A sample of sodium chloride crystals Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 47 SECTION 2.7 Ions and Ionic Compounds mental sodium is allowed to react with elemental chlorine, an electron transfers from a neutral sodium atom to a neutral chlorine atom We are left with a Na+ ion and a Cl- ion Because objects of opposite charge attract, the Na+ and the Cl- ions bind together to form the compound sodium chloride (NaCl) Sodium chloride, which we know better as common table salt, is an example of an ionic compound, a compound that contains both positively and negatively charged ions We can often tell whether a compound is ionic (consisting of ions) or molecular (consisting of molecules) from its composition In general, cations are metal ions, whereas anions are non-metal ions Consequently, ionic compounds are generally combinations of metals and non-metals, as in NaCl In contrast, molecular compounds are generally composed of non-metals only, as in H2O SAMPLE EXERCISE 2.9 Identifying ionic and molecular compounds Which of the following compounds would you expect to be ionic: N2O, Na2O, CaCl2, SF4? SOLUTION We would predict that Na2O and CaCl2 are ionic compounds because they are composed of a metal combined with a non-metal The other two compounds, composed entirely of non-metals, are predicted (correctly) to be molecular compounds PRACTICE EXERCISE Which of the following compounds are molecular: CBr4, FeS, P4O6, PbF2? Answer: CBr4 and P4O6 The ions in ionic compounds are arranged in three-dimensional structures The arrangement of Na+ and Cl- ions in NaCl is shown in Figure 2.17 Because there is no discrete molecule of NaCl, we are able to write only an empirical formula for this substance In fact, only empirical formulae can be written for ionic compounds We can readily write the empirical formula for an ionic compound if we know the charges of the ions of which the compound is composed Chemical compounds are always electrically neutral Consequently, the ions in an ionic compound always occur in such a ratio that the total positive charge equals the total negative charge Thus there is one Na+ to one Cl- (giving NaCl), one Ba2+ to two Cl- (giving BaCl2) and so forth As you consider these and other examples, you will see that if the charges on the cation and anion are equal, the subscript on each ion will be If the charges are not equal, the charge on one ion (without its sign) will become the subscript on the other ion For example, the ionic compound formed from Mg (which forms Mg2+ ions) and N (which forms N3- ions) is Mg3N2: Mg ϩ N 3Ϫ Mg3N2 CONCEPT CHECK Why don’t we write the formula for the compound formed by Ca2+ and O2- as Ca2O2? SAMPLE EXERCISE 2.10 Using ionic charge to write empirical formulae for ionic compounds What are the empirical formulae of the compounds formed by (a) Al3+ and Cl- ions, (b) Al3+ and O2- ions, (c) Mg2+ and NO3- ions? SOLUTION (a) Three Cl- ions are required to balance the charge of one Al3+ ion Thus the formula is AlCl3 (b) Two Al3+ ions are required to balance the charge of three O2- ions (that is, Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e 47 *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 48 48 CHAPTER Atoms, Molecules and Ions the total positive charge is 6+ and the total negative charge is 6-) Thus the formula is Al2O3 (c) Two NO3- ions are needed to balance the charge of one Mg2ϩ Thus the formula is Mg(NO3)2 In this case the formula for the entire polyatomic ion NO3must be enclosed in parentheses so that it is clear that the subscript applies to all the atoms of that ion P R ACTICE EXERCISE Write the empirical formulae for the compounds formed by the following ions: (a) Na+ and PO43-, (b) Zn2+ and SO42-, (c) Fe3+ and CO32Answers: (a) Na3PO4, (b) ZnSO4, (c) Fe2(CO3)3 (See also Exercises 2.40, 2.41.) MY WORLD OF CHEMISTRY ELEMENTS REQUIRED BY LIVING ORGANISMS The coloured regions of Ǡ FIGURE 2.18 shows the elements essential to life More than 97% of the mass of most organisms is made up of just six of these elements—oxygen, carbon, hydrogen, nitrogen, phosphorus and sulfur Water is the most common compound in living organisms, accounting for at least 70% of the mass of most cells In the solid components of cells, carbon is the most prevalent element by mass Carbon atoms are found in a vast variety of organic molecules, bonded either to other carbon atoms or to atoms of other elements All proteins, for example, H contain the group Li Be 18 He 13 14 15 16 17 B C N O F Ne Na Mg 10 11 12 Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr O N In addition, 23 more elements have been found in various living organisms Five are ions required by all organisms: Ca2+, Cl-, Mg 2+, K + , and Na + Calcium ions, for example, are necessary for the formation of bone and transmission of nervous system signals Many other elements are needed in only very small quantities and consequently are called trace elements For example, trace quantities of copper are required in the diet of humans to aid in the synthesis of haemoglobin C Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe R which occurs repeatedly in the molecules (R is either an H atom or a combination of atoms, such as CH3.) Six most abundant essential elements Five next most abundant essential elements Elements needed only in trace quantities į FIGURE 2.18 Elements essential to life 2.8 | NAMING INORGANIC COMPOUNDS To obtain information about a particular substance, you must know its name and chemical formula The names and formulae of compounds are essential vocabulary in chemistry The system used in naming substances is called chemical nomenclature, from the Latin words nomen (name) and calare (to call) There are now more than 50 million known chemical substances Naming them all would be a hopelessly complicated task if each had a special name independent of all others Many important substances that have been known for a long time, such as water (H2O) and ammonia (NH3), have individual, traditional names (so-called ‘common’ names) For most substances, however, we rely on a systematic set of rules that leads to an informative and unique name for each substance, a name based on the composition of the substance The rules for chemical nomenclature are based on the division of substances into categories The major division is between organic and inorganic compounds Organic compounds contain carbon, usually in combination with Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 49 SECTION 2.8 Naming Inorganic Compounds 49 hydrogen, oxygen, nitrogen or sulfur All others are inorganic compounds Early chemists associated organic compounds with plants and animals, and they associated inorganic compounds with the non-living portion of our world Although this distinction between living and non-living matter is no longer pertinent, the classification between organic and inorganic compounds continues to be useful Among inorganic compounds we consider three categories: ionic compounds, molecular compounds and acids Names and Formulae of Ionic Compounds Recall from Section 2.7 that ionic compounds usually consist of metal ions combined with non-metal ions The metals form positive ions, and the non-metals form negative ions Let’s examine the naming of positive ions, then the naming of negative ones After that, we will consider how to put the names of the ions together to identify the complete ionic compound Positive ions (cations) (a) Cations formed from metal atoms have the same name as the metal: Na+ sodium ion Zn2 + zinc ion Al3 + aluminium ion Ions formed from a single atom are called monatomic ions (b) If a metal can form cations with different charges, the positive charge is indicated by a Roman numeral in parentheses following the name of the metal: Fe2 + iron(II) ion Cu+ copper(I) ion Fe3 + iron(III) ion Cu2 + copper(II) ion Ions of the same element that have different charges exhibit different properties, such as different colours (Ĭ FIGURE 2.19) Most of the metals that can form cations with different charges are transition metals, elements that occur in the middle block of elements, from group to group 12 in the periodic table The charges of these ions are indicated by Roman numerals as mentioned above The metals that form only one cation are those of group (Li+, Na+, K+, Rb+ and Cs+) and group (Mg2+, Ca2+, Sr2+ and Ba2+), as well as Al3+ (group 13) and two transition metal ions: Ag+ (group 11) and Zn2+ (group 12) Charges are not expressed explicitly when naming these ions However, if there is any doubt in your mind whether a metal forms more than one cation, use a Roman numeral to indicate the charge It is never wrong to so, even though it may be unnecessary An older method still widely used for distinguishing between two differently charged ions of a metal is to apply the ending -ous or -ic These endings represent the lower and higher charged ions, respectively They are added to the root of the element’s Latin name: Fe2 + ferrous ion Cu+ cuprous ion Fe3 + ferric ion Cu2 + cupric ion Although we will avoid using these older names in this text, you might encounter them elsewhere (c) Cations formed from non-metal atoms have names that end in -ium: NH4+ ammonium ion H3O+ hydronium ion į FIGURE 2.19 Different ions of the same element have different properties Both substances shown are compounds of iron The substance on the left is Fe3O4, which contains Fe2+ and Fe3+ ions The substance on the right is Fe2O3, which contains only Fe3+ ions Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 50 50 CHAPTER Atoms, Molecules and Ions TABLE 2.4 • Common cations* Charge 1+ Formula ؉ H Li+ hydrogen ion lithium ion Na؉ sodium ion K؉ potassium ion Cs 2+ Name + Formula NH4 Cu+ ؉ ammonium ion copper(I) or cuprous ion caesium ion Ag؉ silver ion Mg2؉ Ca2؉ magnesium ion Co2+ cobalt(II) or cobaltous ion calcium ion Cu2؉ copper(II) or cupric ion 2+ 2؉ Sr strontium ion Fe Ba2+ barium ion Mn2+ 2؉ iron(II) or ferrous ion manganese(II) or manganous ion 2+ Zn zinc ion Hg2 mercury(I) or mercurous ion Cd2+ cadmium ion Hg2؉ mercury(II) or mercuric ion 2+ Ni Pb2؉ 3؉ Al aluminium ion nickel(II) or nickelous ion lead(II) or plumbous ion 2+ tin(II) or stannous ion 3+ chromium(III) or chromic ion Sn 3+ Name Cr Fe3؉ iron(III) or ferric ion *The ions we use most often in this course are in bold Learn them first These two ions are the only ions of this kind that we encounter frequently in the text They are both polyatomic The vast majority of cations you will encounter in this text are monatomic metal ions The names and formulae of some common cations are shown in į TABLE 2.4 and are also included in a table of common ions at the end of this text The ions listed on the left in Table 2.4 are the monatomic ions that not have variable charges Those listed on the right are either polyatomic cations or cations with variable charges The Hg22+ ion is unusual because this metal ion is not monatomic It is called the mercury(I) ion because it can be thought of as two Hg+ ions fused together The cations that you will encounter most frequently are shown in bold These are the ones you should learn first CONCEPT CHECK Why is CrO named using a Roman numeral, chromium(II) oxide, whereas CaO is named without a Roman numeral in the name, calcium oxide? Negative ions (anions) (a) The names of monatomic anions are formed by replacing the ending of the name of the element with -ide: H - hydride ion O2 - oxide ion N3 - nitride ion A few simple polyatomic anions also have names ending in -ide: OH- hydroxide ion CN- cyanide ion O22- peroxide ion (b) Polyatomic anions containing oxygen have names ending in -ate or -ite These anions are called oxyanions The ending -ate is used for the most Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 51 SECTION 2.8 Naming Inorganic Compounds 51 FIGURE IT OUT Name the anion obtained by removing one oxygen atom from the perbromate ion, BrO4- _ide (chloride, ClϪ) Simple anion Oxyanions ϩO atom per ate (perchlorate, ClO4Ϫ) _ate (chlorate, ClO3Ϫ) ϪO atom _ite (chlorite, ClO2Ϫ) ϪO atom hypo ite (hypochlorite, ClOϪ) Common or representative oxyanion į FIGURE 2.20 Summary of the procedure for naming anions The first part of the name, such as ‘chlor’ for chlorine or ‘sulf’ for sulfur, goes in the blank common oxyanion of an element The ending -ite is used for an oxyanion that has the same charge but one O atom fewer: SO42- sulfate ion SO32- sulfite ion NO3 - nitrate ion NO2- nitrite ion Prefixes are used when the series of oxyanions of an element extends to four members, as with the halogens The prefix per- usually indicates one more O atom than the oxyanion ending in -ate; the prefix hyponormally indicates one O atom fewer than the oxyanion ending in -ite: ClO4ClO3؊ ClO2ClO- perchlorate ion (one more O atom than chlorate) chlorate ion chlorite ion (one O atom fewer than chlorate) hypochlorite ion (one O atom fewer than chlorite) These rules are summarised in į FIGURE 2.20 CONCEPT CHECK What information is conveyed by the endings -ide, -ate and -ite in the name of an anion? Students often have a hard time remembering the number of oxygen atoms in the various oxyanions and the charges of these ions Ĭ FIGURE 2.21 lists the oxyanions of C, N, P, S and Cl that contain the maximum number of O atoms There is a periodic pattern to these formulae that can help you remember them Notice that C and N, which are in the second period of the periodic table, have only three O atoms each, whereas P, S and Cl, which are in the third period, have four O atoms each If we begin at the lower right side of the figure, with 14 CO32– Carbonate ion 15 – NO3 Nitrate ion PO43– Phosphate ion 16 SO42– Sulfate ion 17 ClO4– Perchlorate ion ǡ FIGURE 2.21 Common oxyanions The composition and charge of common oxyanions are related to their location in the periodic table Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 52 52 CHAPTER Atoms, Molecules and Ions Cl, we see that the charges increase from right to left, from 1- for Cl (ClO4-) to 3- for P (PO43-) In the second period the charges also increase from right to left, from 1- for N (NO3-) to 2- for C (CO32-) Each anion shown in Figure 2.21 has a name ending in -ate The ClO4- ion also has a per- prefix If you know the rules summarised in Figure 2.20 and the names and formulae of the five oxyanions in Figure 2.21, you can deduce the names for the other oxyanions of these elements CONCEPT CHECK 10 Predict the formulae for the borate ion and silicate ion, assuming that they contain a single B and Si atom, respectively, and follow the trends shown in Figure 2.21 SAMPLE EXERCISE 2.11 Determining the formula of an oxyanion from its name Based on the formula for the sulfate ion, predict the formula for (a) the selenate ion and (b) the selenite ion (Sulfur and selenium are both members of group 16 and form analogous oxyanions.) S O LUTION (a) The sulfate ion is SO42- The analogous selenate ion is therefore SeO42- (b) The ending -ite indicates an oxyanion with the same charge but one O atom fewer than the corresponding oxyanion that ends in -ate Thus the formula for the selenite ion is SeO32- P R ACTICE EXERCISE The formula for the bromate ion is analogous to that for the chlorate ion Write the formula for the hypobromite and perbromate ions Answer: BrO- and BrO4(See also Exercises 2.42, 2.43.) (c) Anions derived by adding H+ to an oxyanion are named by adding as a prefix the word hydrogen or dihydrogen, as appropriate: CO32 HCO3 - carbonate ion PO43 - hydrogen carbonate ion H2PO4 - dihydrogen phosphate ion phosphate ion Notice that each H+ reduces the negative charge of the parent anion by one An older method for naming some of these ions is to use the prefix bi- Thus the HCO3- ion is commonly called the bicarbonate ion, and HSO4- is sometimes called the bisulfate ion The names and formulae of the common anions are listed in Ǡ TABLE 2.5 and on the back inside cover of this text Those anions whose names end in -ide are listed on the left of Table 2.5, and those whose names end in -ate are listed on the right The most common of these ions are shown in bold These are the ones you should learn first The formulae of the ions whose names end with -ite can be derived from those ending in -ate by removing an O atom Notice the location of the monatomic ions in the periodic table Those of group 17 always have a 1- charge (F-, Cl-, Br- and I-) and those of group 16 have a 2- charge (O2- and S2-) Ionic compounds Names of ionic compounds consist of the cation name followed by the anion name: CaCl2 Al(NO3)3 Cu(ClO4)2 calcium chloride aluminium nitrate copper(II) perchlorate (or cupric perchlorate) Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 53 SECTION 2.8 Naming Inorganic Compounds TABLE 2.5 • Common anions* Charge 1- 2- 3- Formula H - Name hydride ion Formula Name ؊ CH3COO (or C2H3O2- ) ClO3ClO4؊ NO3؊ MnO4- acetate ion F؊ Cl؊ Br؊ I؊ CNOH؊ fluoride ion chloride ion bromide ion iodide ion cyanide ion hydroxide ion O2؊ O22- oxide ion peroxide ion CO32؊ CrO42- carbonate ion chromate ion S2؊ sulfide ion Cr2O72SO42؊ dichromate ion sulfate ion N3- nitride ion PO43؊ phosphate ion chlorate ion perchlorate ion nitrate ion permanganate ion *The ions we use most often are in bold Learn them first In the chemical formulae for aluminium nitrate and copper(II) perchlorate, parentheses followed by the appropriate subscript are used because the compounds contain two or more polyatomic ions SAMPLE EXERCISE 2.12 Determining the names of ionic compounds from their formulae Name the following compounds: (a) K2SO4, (b) Ba(OH)2, (c) FeCl3 SOLUTION Each compound is ionic and is named using the guidelines we have already discussed In naming ionic compounds, it is important to recognise polyatomic ions and to determine the charge of cations with variable charge (a) The cation in this compound is K+, and the anion is SO42- (If you thought the compound contained S2- and O2- ions, you failed to recognise the polyatomic sulfate ion.) Putting together the names of the ions, we have the name of the compound, potassium sulfate (b) In this case the compound is composed of Ba2+ and OH- ions Ba2+ is the barium ion and OH- is the hydroxide ion Thus the compound is called barium hydroxide (c) You must determine the charge of Fe in this compound because an iron atom can form more than one cation Because the compound contains three Cl- ions, the cation must be Fe3+, which is the iron(III), or ferric, ion The Cl- ion is the chloride ion Thus the compound is iron(III) chloride or ferric chloride PRACTICE EXERCISE Name the following compounds: (a) NH4Br, (b) Cr2O3, (c) Co(NO3)2 Answers: (a) Ammonium bromide, (b) chromium(III) oxide, (c) cobalt(II) nitrate (See also Exercises 2.44, 2.45.) SAMPLE EXERCISE 2.13 Determining the formulae of ionic compounds from their names Write the chemical formulae for the following compounds: (a) potassium sulfide, (b) calcium hydrogen carbonate, (c) nickel(II) perchlorate SOLUTION In going from the name of an ionic compound to its chemical formula, you must know the charges of the ions to determine the subscripts (a) The potassium ion is K+ and the sulfide ion is S2- Because ionic compounds are electrically neutral, two K+ ions are required to balance the charge of one S2- ion, giving the empirical formula of the compound, K2S (b) The calcium ion is Ca2+ The carbonate ion is CO32-, so the Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e 53 *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 54 54 CHAPTER Atoms, Molecules and Ions hydrogen carbonate ion is HCO3- Two HCO3- ions are needed to balance the positive charge of Ca2+, giving Ca(HCO3)2 (c) The nickel(II) ion is Ni2+ The perchlorate ion is ClO4- Two ClO4- ions are required to balance the charge on one Ni2+ ion, giving Ni(ClO4)2 P R ACTICE EXERCISE Give the chemical formula for (a) magnesium sulfate, (b) silver sulfide, (c) lead(II) nitrate Answers: (a) MgSO4, (b) Ag2S, (c) Pb(NO3)2 (See also Exercises 2.46, 2.47.) Names and Formulae of Acids Acids are an important class of hydrogen-containing compounds and are named in a special way For our present purposes, an acid is a substance whose molecules yield hydrogen ions (H+) when dissolved in water When we encounter the chemical formula for an acid at this stage of the course, it will be written with H as the first element, as in HCl and H2SO4 An acid is composed of an anion connected to enough H+ ions to neutralise, or balance, the anion’s charge Thus the SO42- ion requires two H+ ions, forming H2SO4 The name of an acid is related to the name of its anion, as summarised in Ĭ FIGURE 2.22 Acids containing anions whose names end in -ide are named by changing the -ide ending to -ic, adding the prefix hydro- to this anion name, and then following with the word acid, as in the following examples: Anion Corresponding acid Cl- (chloride) S2- (sulfide) HCl (hydrochloric acid) H2S (hydrosulfuric acid) Acids containing anions whose names end in -ate or -ite are named by changing -ate to -ic and -ite to -ous, and then adding the word acid Prefixes in the anion name are retained in the name of the acid These rules are illustrated by the oxyacids of chlorine: Anion Corresponding acid ClO4- (perchlorate) ClO3- (chlorate) ClO2- (chlorite) ClO- (hypochlorite) HClO4 (perchloric acid) HClO3 (chloric acid) HClO2 (chlorous acid) HClO (hypochlorous acid) Anion _ide (chloride, ClϪ) Acid add Hϩ ions _ate add Hϩ (chlorate, ClO3Ϫ) (perchlorate, ClO4Ϫ) ions Ǡ FIGURE 2.22 How anion names and acid names relate The prefixes per- and hypo- are retained in going from the anion to the acid hydro ic acid (hydrochloric acid, HCl) _ic acid (chloric acid, HClO3) (perchloric acid, HClO4) _ous acid _ite add Hϩ (chlorous acid, HClO2) (chlorite, ClO2Ϫ) (hypochlorous acid, HClO) (hypochlorite, ClO Ϫ) ions Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 55 SECTION 2.8 SAMPLE EXERCISE 2.14 Naming Inorganic Compounds 55 Relating the names and formulae of acids Name the following acids: (a) HCN, (b) HNO3, (c) H2SO4, (d) H2SO3 SOLUTION (a) The anion from which this acid is derived is CN-, the cyanide ion Because this ion has an -ide ending, the acid is given a hydro- prefix and an -ic ending: hydrocyanic acid Only water solutions of HCN are referred to as hydrocyanic acid: the pure compound, which is a gas under normal conditions, is called hydrogen cyanide Both hydrocyanic acid and hydrogen cyanide are extremely toxic (b) Because NO3- is the nitrate ion, HNO3 is called nitric acid (the -ate ending of the anion is replaced with an -ic ending in naming the acid) (c) Because SO42- is the sulfate ion, H2SO4 is called sulfuric acid (d) Because SO32- is the sulfite ion, H2SO3 is sulfurous acid (the -ite ending of the anion is replaced with an -ous ending) PRACTICE EXERCISE Give the chemical formulae for (a) hydrobromic acid, (b) carbonic acid Answers: (a) HBr, (b) H2CO3 (See also Exercises 2.48, 2.49.) Names and Formulae of Binary Molecular Compounds The procedures used for naming binary (two-element) molecular compounds are similar to those used for naming ionic compounds The name of the element further to the left in the periodic table is usually written first An exception to this rule occurs in the case of compounds that contain oxygen Oxygen is always written last except when combined with fluorine If both elements are in the same group in the periodic table, the one having the higher atomic number is named first The name of the second element is given an -ide ending Greek prefixes (Ǡ TABLE 2.6) are used to indicate the number of atoms of each element The prefix mono- is never used with the first element When the prefix ends in a or o and the name of the second element begins with a vowel (such as oxide), the a or o of the prefix is often dropped The following examples illustrate these rules: Cl2O dichlorine monoxide N2O4 dinitrogen tetroxide NF3 nitrogen trifluoride P4S10 tetraphosphorus decasulfide It is important to realise that you cannot predict the formulae of most molecular substances in the same way that you predict the formulae of ionic compounds That is why we name molecular compounds using prefixes that explicitly indicate their composition However, molecular compounds that contain hydrogen and one other element are an important exception These compounds can be treated as if they were neutral substances containing H+ ions and anions Thus you can predict that the substance whose name is hydrogen chloride has the formula HCl, containing one H+ to balance the charge of one Cl- (The name hydrogen chloride is used only for the pure compound; water solutions of HCl are called hydrochloric acid.) Similarly, the formula for hydrogen sulfide is H2S because two H+ are needed to balance the charge on S2- TABLE 2.6 • Prefixes used in naming binary compounds formed between non-metals Prefix MonoDiTriTetraPentaHexaHeptaOctaNonaDeca- Meaning 10 Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 56 56 CHAPTER Atoms, Molecules and Ions SAMPLE EXERCISE 2.15 Relating the names and formulae of binary molecular compounds Name the following compounds: (a) SO2, (b) PCl5, (c) N2O3 S O LUTION The compounds consist entirely of non-metals, so they are probably molecular rather than ionic Using the prefixes in Table 2.6, we have (a) sulfur dioxide, (b) phosphorus pentachloride and (c) dinitrogen trioxide P R ACTICE EXERCISE Give the chemical formula for (a) silicon tetrabromide, (b) disulfur dichloride Answers: (a) SiBr4, (b) S2Cl2 (See also Exercises 2.50, 2.51.) 2.9 | SOME SIMPLE ORGANIC COMPOUNDS The study of compounds of carbon is called organic chemistry and, as noted earlier, compounds that contain carbon and hydrogen, often in combination with oxygen, nitrogen or other elements, are called organic compounds We will examine organic compounds in detail in Chapter 22, but here we present a brief introduction to some of the simplest organic compounds Alkanes Compounds that contain only carbon and hydrogen are called hydrocarbons In the simplest class of hydrocarbons, alkanes, each carbon is bonded to four other atoms The three smallest alkanes are methane (CH4), ethane (C2H6) and propane (C3H8) The structural formulae of these three alkanes are as follows: H H C H H H Methane H H C C H H H H Ethane H H H C C C H H H H Propane Although hydrocarbons are binary molecular compounds, they are not named like the binary inorganic compounds discussed in Section 2.8 Instead, each alkane has a name that ends in -ane The alkane with four carbons is called butane For alkanes with five or more carbons, the names are derived from prefixes like those in Table 2.6 An alkane with eight carbon atoms, for example, is octane (C8H18), where the octa- prefix for eight is combined with the -ane ending for an alkane Some Derivatives of Alkanes Other classes of organic compounds are obtained when one or more hydrogen atoms in an alkane are replaced with functional groups, which are specific groups of atoms An alcohol, for example, is obtained by replacing a H atom of an alkane with an ϪOH group The name of the alcohol is derived from that of the alkane by adding an -ol ending: H H C OH H Methanol H H H C C H H Ethanol OH H H H H C C C H H H OH 1-Propanol Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e *Brown 3e - ch02 (India)_BLB03_002-037 9/10/13 2:01 PM Page 57 SECTION 2.9 Some Simple Organic Compounds Alcohols have properties that are very different from the properties of the alkanes from which the alcohols are obtained For example, methane, ethane and propane are all colourless gases under normal conditions, whereas methanol, ethanol and propanol are colourless liquids We will discuss the reasons for these differences in Chapter 11 The prefix ‘1’ in the name 1-propanol indicates that the replacement of H with OH has occurred at one of the ‘outer’ carbon atoms rather than the ‘middle’ carbon atom A different compound, called 2-propanol, is obtained when the OH functional group is attached to the middle carbon atom (Ǡ FIGURE 2.23) Compounds with the same molecular formula but different arrangements of atoms are called isomers There are many different kinds of isomers, as we will discover later in this book What we have here with 1-propanol and 2-propanol are structural isomers, compounds having the same molecular formula but different structural formulae OH group on end carbon 1-Propanol OH group on middle carbon CONCEPT CHECK 11 Draw the structural formulae of the two isomers of butane, C4H10 2-Propanol Much of the richness of organic chemistry is possible because organic compounds can form long chains of carbon–carbon bonds The series of alkanes that begins with methane, ethane and propane and the series of alcohols that begins with methanol, ethanol and propanol can both be extended for as long as we desire, in principle The properties of alkanes and alcohols change as the chains get longer Octanes, which are alkanes with eight carbon atoms, are liquids under normal conditions If the alkane series is extended to tens of thousands of carbon atoms, we obtain polyethene, a solid substance that is used to make thousands of plastic products, such as plastic bags, food containers and laboratory equipment SAMPLE EXERCISE 2.16 į FIGURE 2.23 The two forms (isomers) of propanol Writing structural and molecular formulae for hydrocarbons Assuming the carbon atoms in pentane are in a linear chain, write (a) the structural formula and (b) the molecular formula for this alkane SOLUTION (a) Alkanes contain only carbon and hydrogen, and each carbon is attached to four other atoms The name pentane contains the prefix penta- for five (Table 2.6), and we are told that the carbons are in a linear chain If we then add enough hydrogen atoms to make four bonds to each carbon, we obtain the structural formula: H H H H H H C C C C C H H H H H H This form of pentane is often called n-pentane, where the n- stands for ‘normal’ because all five carbon atoms are in one line in the structural formula (b) Once the structural formula is written, we determine the molecular formula by counting the atoms present Thus n-pentane has the molecular formula C5H12 PRACTICE EXERCISE (a) What is the molecular formula of butane, the alkane with four carbons? (b) What are the name and molecular formula of an alcohol derived from butane? Answers: (a) C4H10, (b) butanol, C4H10O or C4H9OH (See also Exercise 2.55(c).) Copyright © Pearson Australia (a division of Pearson Australia Group Pty Ltd) 2014 – 9781442554603 – Brown/Chemistry: The central science 3e 57 ... from the United States edition entitled Chemistry: The Central Science, 12th edition, ISBN 01321696727 by Brown, Theodore L.; LeMay, H Eugene Jr; Bursten, Bruce E.; Murphy, Catherine J.; Woodward,. .. bring the concepts to life Finally, to Theodore Brown, Eugene LeMay, Bruce Bursten, Catherine Murphy and Patrick Woodward we thank you sincerely for allowing us to use your textbook as the foundation... 9781442554603 – Brown /Chemistry: The central science 3e xxv MasteringChemistry for Chemistry: The Central Science, 3rd Edition A Guided Tour for Students and Educators Reading Quizzes: The Item Library