(BQ) Part 1 book Descriptive inorganic chemistry has contents: The electronic structure of the atom A review; an overview of the periodic table; covalent bondin; ionic bonding; solvent systems and acid base behavior; oxidation and reduction,...and other contents.
This page intentionally left blank Descriptive Inorganic Chemistry FIFTH EDITION Geoff Rayner-Canham Sir Wilfred Grenfell College Memorial University Tina Overton University of Hull W H FREEMAN AND COMPANY NEW YORK Publisher: Clancy Marshall Acquisitions Editors: Jessica Fiorillo/Kathryn Treadway Marketing Director: John Britch Media Editor: Dave Quinn Cover and Text Designer: Vicki Tomaselli Senior Project Editor: Mary Louise Byrd Illustrations: Network Graphics/Aptara Senior Illustration Coordinator: Bill Page Production Coordinator: Susan Wein Composition: Aptara Printing and Binding: World Color Versailles Library of Congress Control Number: 2009932448 ISBN-13: 978-1-4292-2434-5 ISBN-10: 1-4292-1814-2 @2010, 2006, 2003, 2000 by W H Freeman and Company All rights reserved Printed in the United States of America First printing W H Freeman and Company 41 Madison Avenue New York, NY 10010 Houndmills, Basingstoke RG21 6XS, England www.whfreeman.com Overview CHAPTER The Electronic Structure of the Atom: A Review CHAPTER An Overview of the Periodic Table 19 CHAPTER Covalent Bonding 41 CHAPTER Metallic Bonding 81 CHAPTER Ionic Bonding 93 CHAPTER Inorganic Thermodynamics 113 CHAPTER Solvent Systems and Acid-Base Behavior 137 CHAPTER Oxidation and Reduction 167 CHAPTER Periodic Trends 191 CHAPTER 10 Hydrogen 227 CHAPTER 11 The Group Elements: The Alkali Metals 245 CHAPTER 12 The Group Elements: The Alkaline Earth Metals 271 CHAPTER 13 The Group 13 Elements 291 CHAPTER 14 The Group 14 Elements 315 CHAPTER 15 The Group 15 Elements: The Pnictogens 363 CHAPTER 16 The Group 16 Elements: The Chalcogens 409 CHAPTER 17 The Group 17 Elements: The Halogens 453 CHAPTER 18 The Group 18 Elements: The Noble Gases 487 CHAPTER 19 Transition Metal Complexes 499 CHAPTER 20 Properties of the 3d Transition Metals 533 CHAPTER 21 Properties of the 4d and 5d Transition Metals 579 CHAPTER 22 The Group 12 Elements 599 CHAPTER 23 Organometallic Chemistry 611 On the Web www.whfreeman.com/descriptive5e CHAPTER 24 The Rare Earth and Actinoid Elements Appendices Index 651w A-1 I-1 iii This page intentionally left blank Contents What Is Descriptive Inorganic Chemistry? Preface Acknowledgments Dedication xiii xv xix xxi CHAPTER The Electronic Structure of the Atom: A Review Atomic Absorption Spectroscopy 1.1 1.2 1.3 1.4 1.5 1.6 The Schrödinger Wave Equation and Its Significance Shapes of the Atomic Orbitals The Polyelectronic Atom Ion Electron Configurations Magnetic Properties of Atoms Medicinal Inorganic Chemistry: An Introduction 14 15 16 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 Molecular Orbitals for Period Diatomic Molecules Molecular Orbitals for Heteronuclear Diatomic Molecules A Brief Review of Lewis Structures Partial Bond Order Formal Charge Valence-Shell Electron-Pair Repulsion Rules The Valence-Bond Concept Network Covalent Substances Intermolecular Forces 46 50 51 53 54 54 59 61 63 The Origins of the Electronegativity Concept 65 3.13 3.13 66 72 Molecular Symmetry Symmetry and Vibrational Spectroscopy Transient Species—A New Direction for Inorganic Chemistry 74 3.15 Covalent Bonding and the Periodic Table 78 CHAPTER CHAPTER An Overview of the Periodic Table 2.1 2.2 2.3 19 Organization of the Modern Periodic Table 21 Existence of the Elements 23 Stability of the Elements and Their Isotopes 24 Metallic Bonding 81 4.1 4.2 4.3 4.4 4.5 81 82 84 86 87 Metallic Bonding Bonding Models Structure of Metals Unit Cells Alloys The Origin of the Shell Model of the Nucleus 26 Memory Metal: The Shape of Things to Come 88 2.4 2.5 2.6 2.7 27 29 33 35 4.6 4.7 89 90 Classifications of the Elements Periodic Properties: Atomic Radius Periodic Properties: Ionization Energy Periodic Properties: Electron Affinity Alkali Metal Anions 37 2.8 37 The Elements of Life CHAPTER Covalent Bonding 41 3.1 3.2 3.3 42 43 Models of Covalent Bonding Introduction to Molecular Orbitals Molecular Orbitals for Period Diatomic Molecules 44 Nanometal Particles Magnetic Properties of Metals CHAPTER Ionic Bonding 93 5.1 5.2 5.3 5.4 5.5 93 95 96 99 5.6 The Ionic Model and the Size of Ions Hydrated Salts Polarization and Covalency Ionic Crystal Structures Crystal Structures Involving Polyatomic Ions The Bonding Continuum Concrete: An Old Material with a New Future 105 106 109 v vi Contents 8.8 CHAPTER Inorganic Thermodynamics 6.1 6.2 6.3 6.4 Thermodynamics of the Formation of Compounds Formation of Ionic Compounds The Born-Haber Cycle Thermodynamics of the Solution Process for Ionic Compounds Formation of Covalent Compounds 113 114 120 122 8.9 8.10 8.11 8.12 8.13 Electrode Potentials as Thermodynamic Functions Latimer (Reduction Potential) Diagrams Frost (Oxidation State) Diagrams Pourbaix Diagrams Redox Synthesis Biological Aspects 124 127 CHAPTER The Hydrogen Economy 128 Periodic Trends 6.6 129 9.1 9.2 9.3 6.5 Thermodynamic versus Kinetic Factors CHAPTER Group Trends Periodic Trends in Bonding Isoelectronic Series in Covalent Compounds Trends in Acid-Base Properties The (n) Group and (n ϩ 10) Group Similarities 177 178 180 182 184 185 191 192 195 199 201 Solvent Systems and Acid-Base Behavior 137 7.1 7.2 138 142 Chemical Topology 206 Antacids 144 9.6 7.3 147 Solvents Brønsted-Lowry Acids Brønsted-Lowry Bases 9.4 9.5 202 Isomorphism in Ionic Compounds 207 209 210 Cyanide and Tropical Fish 148 New Materials: Beyond the Limitations of Geochemistry 7.4 148 9.7 Superacids and Superbases 150 Lithium and Mental Health 211 7.5 7.6 7.7 7.8 7.9 153 155 156 158 161 9.8 9.9 9.10 9.11 9.12 The “Knight’s Move” Relationship The Early Actinoid Relationships The Lanthanoid Relationships “Combo” Elements Biological Aspects 212 215 216 217 221 Thallium Poisoning: Two Case Histories 223 Trends in Acid-Base Behavior Acid-Base Reactions of Oxides Lewis Theory Pearson Hard-Soft Acid-Base Concepts Applications of the HSAB Concept Biological Aspects Diagonal Relationships CHAPTER Oxidation and Reduction 167 CHAPTER 10 8.1 8.2 8.3 167 168 Hydrogen 227 10.1 10.2 228 229 8.4 8.5 8.6 Redox Terminology Oxidation Number Rules Determination of Oxidation Numbers from Electronegativities The Difference between Oxidation Number and Formal Charge Periodic Variations of Oxidation Numbers Redox Equations 169 171 172 173 Isotopes of Hydrogen Nuclear Magnetic Resonance Isotopes in Chemistry 230 10.3 Properties of Hydrogen 231 Searching the Depths of Space for the Trihydrogen Ion 233 10.4 10.5 233 237 Hydrides Water and Hydrogen Bonding Chemosynthesis: Redox Chemistry on the Seafloor 175 Water: The New Wonder Solvent 238 8.7 176 10.6 239 Quantitative Aspects of Half-Reactions Clathrates Contents 10.7 Biological Aspects of Hydrogen Bonding 241 Is There Life Elsewhere in Our Solar System? 242 10.8 242 Element Reaction Flowchart vii Biomineralization: A New Interdisciplinary “Frontier” 284 12.10 12.11 12.12 12.15 284 285 286 287 Calcium Sulfate Calcium Carbide Biological Aspects Element Reaction Flowcharts CHAPTER 11 The Group Elements: The Alkali Metals 11.1 11.2 11.3 Group Trends Features of Alkali Metal Compounds Solubility of Alkali Metal Salts CHAPTER 13 245 246 247 249 Mono Lake 250 11.4 11.5 11.6 11.7 11.8 11.9 252 255 256 257 259 261 Lithium Sodium Potassium Oxides Hydroxides Sodium Chloride Salt Substitutes 261 11.10 11.11 11.12 11.13 11.14 262 262 264 264 Potassium Chloride Sodium Carbonate Sodium Hydrogen Carbonate Ammonia Reaction Ammonium Ion as a Pseudo– Alkali-Metal Ion 11.15 Biological Aspects 11.16 Element Reaction Flowcharts 265 265 266 The Group 13 Elements 291 13.1 13.2 13.3 292 293 294 Inorganic Fibers 295 13.4 295 12.1 12.2 12.3 12.4 12.5 12.6 12.7 Group Trends Features of Alkaline Earth Metal Compounds Beryllium Magnesium Calcium and Barium Oxides Calcium Carbonate 298 13.5 13.6 13.7 13.8 13.9 13.10 13.11 13.12 300 301 306 307 308 309 309 311 Boron Halides Aluminum Aluminum Halides Aluminum Potassium Sulfate Spinels Aluminides Biological Aspects Element Reaction Flowcharts CHAPTER 14 The Group 14 Elements 14.1 14.2 14.3 Group Trends Contrasts in the Chemistry of Carbon and Silicon Carbon 315 316 316 318 The Discovery of Buckminsterfullerene 322 271 14.4 14.5 325 326 272 275 276 278 279 280 Moissanite: The Diamond Substitute 327 14.6 14.7 328 330 271 How Was Dolomite Formed? 281 12.8 12.9 282 283 Cement Calcium Chloride Boranes Boron Neutron Capture Therapy CHAPTER 12 The Group Elements: The Alkaline Earth Metals Group Trends Boron Borides Isotopes of Carbon Carbides Carbon Monoxide Carbon Dioxide Carbon Dioxide, Supercritical Fluid 332 14.8 14.9 14.10 14.11 14.12 333 335 335 338 339 Carbonates and Hydrogen Carbonates Carbon Sulfides Carbon Halides Methane Cyanides viii 14.13 14.14 14.15 14.16 14.17 Contents Silicon Silicon Dioxide Silicates Aluminosilicates Silicones 339 341 343 345 349 Inorganic Polymers 350 14.18 14.19 14.20 14.21 351 352 353 354 Tin and Lead Tin and Lead Oxides Tin and Lead Halides Tetraethyllead TEL: A Case History 355 14.22 Biological Aspects 14.23 Element Reaction Flowcharts 356 359 CHAPTER 15 The Group 15 Elements: The Pnictogens 15.1 15.2 Group Trends Contrasts in the Chemistry of Nitrogen and Phosphorus Overview of Nitrogen Chemistry 363 364 365 368 CHAPTER 16 The Group 16 Elements: The Chalcogens 16.1 16.2 16.3 Group Trends Contrasts in the Chemistry of Oxygen and Sulfur Oxygen Oxygen Isotopes in Geology 16.4 409 410 411 412 412 Bonding in Covalent Oxygen Compounds Trends in Oxide Properties Mixed-Metal Oxides 418 419 421 New Pigments through Perovskites 422 16.7 16.8 16.9 16.10 16.11 16.12 Water Hydrogen Peroxide Hydroxides The Hydroxyl Radical Overview of Sulfur Chemistry Sulfur 422 424 424 426 426 427 Cosmochemistry: Io, the Sulfur-Rich Moon 428 431 432 16.5 16.6 The First Dinitrogen Compound 369 16.13 Hydrogen Sulfide 16.14 Sulfides 15.4 369 Disulfide Bonds and Hair 432 Propellants and Explosives 370 15.5 371 16.15 16.16 16.17 16.18 16.19 16.20 16.21 16.22 16.23 16.24 434 437 438 440 441 443 445 445 446 448 15.3 Nitrogen Nitrogen Hydrides Haber and Scientific Morality 374 15.6 15.7 15.8 15.9 15.10 15.11 15.12 15.13 377 378 379 384 385 386 389 390 Nitrogen Ions The Ammonium Ion Nitrogen Oxides Nitrogen Halides Nitrous Acid and Nitrites Nitric Acid and Nitrates Overview of Phosphorus Chemistry Phosphorus Sulfur Oxides Sulfites Sulfuric Acid Sulfates and Hydrogen Sulfates Other Oxy-Sulfur Anions Sulfur Halides Sulfur-Nitrogen Compounds Selenium Biological Aspects Element Reaction Flowcharts CHAPTER 17 Nauru, the World’s Richest Island 391 15.14 15.15 15.16 15.17 15.18 15.19 393 393 394 395 399 399 The Group 17 Elements: The Halogens 453 Paul Erhlich and His “Magic Bullet” 401 15.29 Element Reaction Flowcharts 402 17.4 17.5 Phosphine Phosphorus Oxides Phosphorus Chlorides Phosphorus Oxo-Acids and Phosphates The Pnictides Biological Aspects 17.1 17.2 17.3 Group Trends Contrasts in the Chemistry of Fluorine and Chlorine Fluorine The Fluoridation of Water 454 455 458 459 Hydrogen Fluoride and Hydrofluoric Acid 460 Overview of Chlorine Chemistry 462 348 CHAPTER 14 • The Group 14 Elements Ceramics The term ceramics describes nonmetallic, inorganic compounds that are prepared by high-temperature treatment The properties of ceramic materials are a function not only of their chemical composition but also of the conditions of their synthesis Typically, the components are finely ground and mixed to a paste with water The paste is then formed into the desired shape and heated to about 900°C At these temperatures, all the water molecules are lost, and numerous high-temperature chemical reactions occur In particular, long needle crystals of mullite, Al6Si2O13, are formed These make a major contribution to the strength of the ceramic material Conventional ceramics are made from a combination of quartz with twodimensional silicates (clays) and three-dimensional silicates (feldspars) Thus, a stoneware used for household plates will have a composition of about 45 percent clay, 20 percent feldspar, and 35 percent quartz By contrast, a dental ceramic for tooth caps is made from about 80 percent feldspar, 15 percent clay, and percent quartz The major interest today, however, is in nontraditional ceramics, particularly metal oxides To form a solid ceramic, the microcrystalline powder is heated to just below its melting point, sometimes under pressure as well Under these conditions, bonding between the crystal surfaces occurs, a process known as sintering Aluminum oxide is a typical example Aluminum oxide ceramic is used as an insulator in automobile spark plugs and as a replacement for bone tissue, such as in artificial hips The most widely used non-oxide ceramic, silicon carbide, was discussed in Section 14.5 As the search for new materials intensifies, boundaries between compound classifications are disappearing Cermets are materials containing cemented grains of metals and ceramic compounds; glassy ceramics are glasses in which a carefully controlled proportion of crystals has been grown Two examples of compounds that can be formed into glassy ceramics are lithium aluminum silicate, Li2Al2Si4O12, and magnesium aluminum silicate, Mg2Al4Si5O18 These materials are nonporous and are known for their extreme resistance to thermal shock That is, they can be heated to red heat and then be plunged into cold water without shattering The major use of this material is in cooking utensils and heat-resistant cooking surfaces Many of these glassy ceramics are produced by Corning Another use for glassy ceramics is in saving lives Flying food and supplies into troubled parts of the world has been very hazardous for the flight crews Their low-flying aircraft are easy targets for small-arms ground fire In the past, all the crew had for protection was relatively ineffective titanium sheets under their seats The U.S and British air forces have now equipped some of their Hercules aircraft with glass ceramic tiles underneath and around the flight deck A high-velocity round hitting the ceramic layer breaks into fragments as it plows into the glassy ceramic, losing most of its kinetic energy in the process This low-mass, low-cost material has the potential to enable emergency agencies to bring food into war-ravaged areas much more safely 14.17 Silicones 349 14.17 Silicones Silicones, more correctly called polysiloxanes, constitute an enormous family of polymers, and they all contain a chain of alternating silicon and oxygen atoms Attached to the silicon atoms are pairs of organic groups, such as the methyl group, CH3 The structure of this simplest silicone is shown in Figure 14.23, where the number of repeating units, n, is very large To synthesize this compound, chloromethane, CH3Cl, is passed over a copper-silicon alloy at 300°C A mixture of compounds is produced, including (CH3)2SiCl2: CH3 CH3 Si CH3 ¢ CH3Cl(g) Si(s) ¡ (CH3)2SiCl2(l) Water is added, causing hydrolysis: (CH3)2SiCl2(l) H2O(l) S (CH3)2Si(OH)2(l) HCl(g) The hydroxo compound then polymerizes, with loss of water: n (CH3)2Si(OH)2(l) S [¬O¬Si(CH3)2¬]n(l) H2O(l) Silicones are used for a wide variety of purposes The liquid silicones are more stable than hydrocarbon oils In addition, their viscosity changes little with temperature, whereas the viscosity of hydrocarbon oils changes dramatically with temperature Thus, silicones are used as lubricants and wherever inert fluids are needed, for example, in hydraulic braking systems Silicones are very hydrophobic (nonwetting); hence, they are used in water-repellent sprays for shoes and other items By the cross-linking of chains, silicone rubbers can be produced Like the silicone oils, the rubbers show great stability to high temperature and to chemical attack Their multitudinous uses include the face-fitting edges for snorkel and scuba masks The rubbers also are very useful in medical applications, such as transfusion tubes However, silicone gels have attained notoriety in their role as a breast implant material While sealed in a polymer sack, they are believed to be harmless The major problem arises when the container walls leak or break The silicone gel can then diffuse into surrounding tissues The chemical inertness of silicones turns from a benefit to a problem, because the body has no mechanism for breaking down the polymer molecules Many medical personnel believe that these alien gel fragments trigger the immune system, thereby causing a number of medical problems The advantages of the silicone polymers over carbon-based polymers result from several factors First, the silicon-oxygen bond in the backbone of the molecule is stronger than the carbon-carbon bond in the organic polymers (452 kJ?mol21 compared to about 346 kJ?mol21), making the silicon-based polymers more resistant to oxidation at high temperatures It is for this reason that high-temperature oil baths always utilize silicone oils, not hydrocarbon oils The absence of substituents on the oxygen atoms in the chain and the wider bond angle (Si¬O¬Si is 143° compared with 109° for C¬C¬C) results in the greater flexibility of a silicone polymer CH3 O Si CH3 CH3 O Si CH3 n CH3 FIGURE 14.23 Structure of the simplest silicone, catena-poly[(dimethylsilicon)-m-oxo] The number of repeating units, n, is very large 350 CHAPTER 14 • The Group 14 Elements Inorganic Polymers S eeing how many types of organic polymers are known, why are there not at least as many inorganic polymers? This is a very good question First of all, the element(s) that constitute the backbone of the polymer must show a tendency to catenate; that is, they must readily form chains And to be useful, the chains must be stable in the presence of atmospheric oxygen Second, at least one of the backbone elements must form more than two covalent bonds; otherwise, side-chain substituents would not be possible It is the variations in side-chain substituents that enables synthetic chemists to “finetune” the properties of a polymer to match the needs of a particular application Organic polymer chemistry is a well-established branch of chemistry, but the study of inorganic polymers is still in its infancy A major reason is the lack of equivalent synthetic pathways to that of organic chemistry Many organic polymers are synthesized by taking multiplebonded monomers and linking them Multiple-bonded inorganic compounds are much harder to synthesize than alkenes and alkynes As a result, different synthetic routes have had to be devised and more routes are still needed As a result of the synthetic difficulties, until recently, there were only three well-developed families of inorganic polymers: the polysiloxanes (silicones), the polyphosphazenes, and the polysilanes Figure 14.24 shows the repeating units of the polysiloxanes and the polyphosphazenes Notice that, by using the phosphorus-nitrogen combination instead of silicon-oxygen, the two series are isoelectronic However, the bonding is different Silicon forms four single bonds and oxygen two (with two lone pairs), whereas phosphorus forms five single bonds and nitrogen three (with one lone pair) Thus, the phosphazines have alternating double bonds along the chain length Like the polysiloxanes, the polyphosphazene polymers are flexible polymers (elastomers) that are superior to organic polymers in their resistance to degradation As a result, polyphosphazenes are used in aerospace and automobile applications The polysilanes, consisting simply of repeating (¬SiR2¬)n, belong to a different family, that of the Group 14 polymers In fact, all of the Group 14 elements form simple polymer chains; thus, there are also polygermanes (¬GeR2¬)n and polystannanes (¬SnR2¬)n Polystannanes are unique in having a backbone solely of metal atoms It is the polysilanes that have proved the most interesting Unlike the carbon-based polymers, the electrons in the silicon backbone are delocalized along the chain As a result, polysilanes are photosensitive and have potential as electrically conducting polymers Among the new polymers being studied are those involving three different elements in their backbone, particularly sulfur, nitrogen, and phosphorus Another bi-element polymer field is that of the boron-nitrogen polymers As we mentioned in Chapter 9, Section 9.11, “combo” elements provide interesting parallels with the element they mimic—in this case, carbon For example, the polyiminoborane shown in Figure 14.25a has been prepared This is analogous in structure to polyacetylene (Figure 14.25b) R R B N Si P R R (a) (b) R (b) FIGURE 14.25 The repeating units of (a) the polyiminoboranes and (b) polyacetylene R O C R (a) R C N FIGURE 14.24 The repeating units of (a) the polysiloxanes and (b) the polyphosphazenes Although most interest is in the polymers themselves, they are also seen as routes to ceramic materials through pyrolysis at very high temperatures Thus, a shape can be molded in the polymer, the polymer heated, and the side chains vaporized, with the backbone ceramic retaining the shape of the object For example, heating polyborazine (¬B3N3H4¬)n results in high-purity boron nitride (BN) 14.18 Tin and Lead 351 14.18 Tin and Lead ϩ3 ⌬G⍜/F or ϪnE⍜ (Vиmol e Ϫ) Tin and lead exist in two oxidation states, 14 and 12 It is possible to explain the existence of the 12 oxidation state in terms of the inert-pair effect, as we did for the 11 oxidation state of thallium in Chapter 9, Section 9.8 The formation of ions of these metals is rare Tin and lead compounds in which the metals are in the 14 oxidation state are covalent, except for a few solid-phase compounds Even when in the 12 oxidation state, tin generally forms covalent bonds, with ionic bonds only being present in compounds in the solid phase Lead, on the other hand, forms the 21 ion in solid and in solution, with the 14 state being strongly oxidizing, as the comparative Frost diagram (Figure 14.26) illustrates Table 14.6 shows that the charge density for Pb21 is relatively low, whereas that for 41 ions is extremely high—high enough to cause the formation of covalent bonds with all but the least polarizable anion, fluoride TABLE 14.6 Charge densities of lead ions Ion Pb21 Pb41 Charge density (C?mm23) 32 196 Tin Tin forms two common allotropes: the shiny metallic allotrope, which is thermodynamically stable above 13°C, and the gray, nonmetallic diamond-structure allotrope, which is stable below that temperature The change at low temperatures to microcrystals of the gray allotrope is slow at first but accelerates rapidly This transition is a particular problem in poorly heated museums, where priceless historical artifacts can crumble into a pile of tin powder The effect can spread from one object to another in contact with it, and this lifelike behavior has been referred to as “tin plague” or “museum disease.” The soldiers of Napoleon’s army had tin buttons fastening their clothes, and they used tin cooking utensils It is believed by some that, during the bitterly cold winter invasion of Russia, the crumbling of buttons, plates, and pans contributed to the low morale and hence to the ultimate defeat of the French troops The existence of both a metallic and a nonmetallic allotrope identifies tin as a real “borderline” or weak metal Tin is also amphoteric, another of its weak metallic properties Thus, tin(II) oxide reacts with acid to give (covalent) tin(II) salts and with bases to form the stannite ion, [Sn(OH)3]2 SnO(s) HCl(aq) S SnCl2(aq) H2O(l) SnO(s) NaOH(aq) H2O(l) S Na1(aq) [Sn(OH)3]2(aq) ϩ2 ϩ1 Ϫ1 Ϫ2 PbO Sn 4ϩ Pb 2ϩ Sn,Pb Sn 2ϩ ϩ4 ϩ2 Ϫ2 Oxidation state FIGURE 14.26 Frost diagram for tin and lead Ϫ4 352 CHAPTER 14 • The Group 14 Elements Lead Lead, the more economically important of the two metals, is a soft, gray-black, dense solid found almost exclusively as lead(II) sulfide, the mineral galena To obtain metallic lead, lead(II) sulfide is heated with air to oxidize the sulfide ions to sulfur dioxide The lead(II) oxide can then be reduced with coke to lead metal: ¢ PbS(s) O2(g) ¡ PbO(s) SO2(g) ¢ PbO(s) C(s) ¡ Pb(l) CO(g) Two major environmental concerns arise in connection with this lead extraction process First, the sulfur dioxide produced contributes to atmospheric pollution unless it is utilized in another process; second, lead dust must not be permitted to escape during the smelting Lead is highly toxic, so the best solution is to recycle the metal At the present time, close to half of the million tonnes of lead used annually come from recycling The aim must be to increase this proportion substantially In particular, it would help if all defunct lead-acid batteries were returned for disassembly and reuse of the lead contained in them Of course, such a move would have a negative economic effect as the result of a decline in employment in the lead-mining industry There would, however, be an increase in employment in the laborintensive recycling and reprocessing sector 14.19 Tin and Lead Oxides The oxides of the heavier members of Group 14 can be regarded as ionic solids Tin(IV) oxide, SnO2, is the stable oxide of tin, whereas lead(II) oxide, PbO, is the stable oxide of lead Lead(II) oxide exists in two crystalline forms, one yellow (massicot) and the other red (litharge) There is also a mixed oxide of lead, Pb3O4 (red lead), which behaves chemically as PbO2?2PbO; hence, its systematic name is lead(II) lead(IV) oxide The chocolate brown lead(IV) oxide, PbO2, is quite stable, and it is a good oxidizing agent Tin(IV) oxide is incorporated in glazes used in the ceramics industry About 3500 tonnes are used annually for this purpose The consumption of lead(II) oxide is much higher, of the order of 250 000 tonnes annually, because it is used to make lead glass and for the production of the electrode surfaces in lead-acid batteries In these batteries, both electrodes are formed by pressing lead(II) oxide into a frame of lead metal The cathode is formed by oxidizing lead(II) oxide to lead(IV) oxide, and the anode is produced by reducing lead(II) oxide to lead metal The electric current arises when lead(IV) oxide is reduced to insoluble lead(II) sulfate in the sulfuric acid electrolyte while the lead metal is oxidized to lead(II) sulfate on the other electrode: PbO2(s) H1(aq) SO422(aq) e2 S PbSO4(s) H2O(l) Pb(s) SO422(aq) S PbSO4(s) e2 14.20 These two half-reactions are reversible Hence, the battery can be recharged by applying an electric current in the reverse direction In spite of a tremendous quantity of research, it has been very difficult to develop a low-cost, lead-free, heavy-duty battery that can perform as well as the lead-acid battery Red lead, Pb3O4, has been used on a large scale as a rust-resistant surface coating for iron and steel Mixed metal oxides, such as calcium lead(IV) oxide, CaPbO3, are now being used as an even more effective protection against salt water for steel structures The structure of CaPbO3 is discussed in Chapter 16, Section 16.6 As mentioned in Section 14.18, the lead(IV) ion is too polarizing to exist in aqueous solution Oxygen can often be used to stabilize the highest oxidation number of an element, and this phenomenon is true for lead Lead(IV) oxide is an insoluble solid in which the Pb41 ions are stabilized in the lattice by the high lattice energy Even then, one can argue that there is considerable covalent character in the structure Addition of an acid, such as nitric acid, gives immediate reduction to the lead(II) ion and the production of oxygen gas: PbO2(s) HNO3(aq) S Pb(NO3)2(aq) H2O(l) O2(g) In the cold, lead(IV) oxide undergoes a double-replacement reaction with concentrated hydrochloric acid to give covalently bonded lead(IV) chloride When warmed, the unstable lead(IV) chloride decomposes to give lead(II) chloride and chlorine gas: PbO2(s) HCl(aq) S PbCl4(aq) H2O(l) PbCl4(aq) S PbCl2(s) Cl2(g) 14.20 Tin and Lead Halides Tin(IV) chloride is a typical covalent metal chloride It is an oily liquid that fumes in moist air to give a gelatinous tin(IV) hydroxide, which we represent as Sn(OH)4 (although it is actually more of a hydrated oxide) and hydrogen chloride gas: SnCl4(l) H2O(l) S Sn(OH)4(s) HCl(g) Like so many compounds, tin(IV) chloride has a small but important role in our lives The vapor of this compound is applied to freshly formed glass, where it reacts with water molecules on the glass surface to form a layer of tin(IV) oxide This very thin layer substantially improves the strength of the glass, a property particularly important in eyeglasses A thicker coating of tin(IV) oxide acts as an electrically conducting layer Aircraft cockpit windows use such a coating An electric current is applied across the conducting glass surface, and the resistive heat that is generated prevents frost formation when the aircraft descends from the cold upper atmosphere Lead(IV) chloride is a yellow oil that, like its tin analog, decomposes in the presence of moisture and explodes when heated Lead(IV) bromide and iodide not exist, because the oxidation potential of these two halogens is sufficient Tin and Lead Halides 353 354 CHAPTER 14 • The Group 14 Elements to reduce lead(IV) to lead(II) The lead(II) chloride, bromide, and iodide are all water-insoluble solids Bright yellow crystals of lead(II) iodide are formed when colorless solutions of lead(II) ion and iodide ion are mixed: Pb21(aq) I2(aq) S PbI2(s) Addition of a large excess of iodide ion causes the precipitate to dissolve, forming a solution of the tetraiodoplumbate(II) ion: PbI2(s) I2(aq) Δ [PbI4]22(aq) 14.21 Tetraethyllead The less electropositive (more weakly metallic) metals form an extensive range of compounds containing metal-carbon bonds The metal-carbon compound that has been produced on the largest scale is tetraethyllead, Pb(C2H5)4, known as TEL Tetraethyllead is a stable compound that has a low boiling point and at one time was produced on a vast scale as a gasoline additive One method of synthesis involves the reaction of a sodium-lead alloy with chloroethane (ethyl chloride): NaPb(s) C2H5Cl(l) high P/D S Pb(C2H5)4(l) Pb(s) NaCl(s) In a gasoline engine, a spark is used to ignite the mixture of fuel and air However, straight-chain hydrocarbons will burn simply when compressed with air—the mode of operation of a diesel engine This reactivity is responsible for the phenomenon of premature ignition (commonly called knocking or pinging), and in addition to making the engine sound as if it is about to fall apart, it can cause severe damage Branched-chain molecules, however, because of their kinetic inertness, require a spark to initiate combustion (Figure 14.27) The measure of the proportion of branched-chain molecules in gasoline is the octane rating; the higher the proportion of branched-chain molecules, the higher the octane rating of the fuel With the demand for higher-performance, higher-compression engines, the need for higher-octane-rated gasoline became acute The addition of TEL to low-octane-rated gasoline increases the octane rating; that is, it prevents premature ignition In the early 1970s, about 500 000 tonnes of TEL were produced annually for addition to gasoline In fact, the U.S Environmental Protection Agency (EPA) allowed up to g of TEL per gallon of gasoline until 1976 FIGURE 14.27 Two hydrocarbons of the same formula, C5H12: (a) a straight-chain isomer and (b) a branched-chain isomer CH3 CH3 CH2 CH2 CH2 CH3 CH3 C CH3 (a) (b) CH3 14.21 Tetraethyllead 355 TEL: A Case History T he story of the use of TEL is a prime example of the dominance of economic benefit over health issues and of the control of information and research The health hazards of lead and, in particular, TEL were known in the early part of the twentieth century, yet the chemical corporations, the gasoline companies, and the auto manufacturers colluded to promote TEL, to support research that promoted TEL, and to discredit those warning of health problems Possible alternative additives, particularly the low-cost ethanol that was popular at the time, were suppressed In fact, Midgley himself had patented ethanol as a means of enhancing the octane rating of gasoline before he became enamored with TEL Leaded gasoline first went on sale in 1923, though it was called ethyl gasoline to hide the fact that it contained lead It was in the same year that the first (of several) deaths occurred at TEL manufacturing plants Even in those days there were concerns about the lead released into the environment by the combustion of TEL For example, the New York Board of Health banned the sale of TEL-enhanced gasoline in 1924, a ban that was lifted in 1926 One of the pioneer fighters against the use of TEL was Alice Hamilton Hamilton, the first female faculty member at Harvard Medical School, was the foremost American industrial toxicologist of her time She expressed her concerns in 1925, the year that the U.S Surgeon General convened a conference to assess the hazards of TEL The position of the automobile industry and that of the gasoline manufacturers (who closely colluded on the issue) was that (1) leaded gasoline was essential to the progress of America, (2) any innovation entailed certain risks, and (3) deaths in TEL manufacturing plants were due to carelessness Dr Yandell Henderson, a physiologist at Yale University, severely criticized the use of leaded gasoline However, a committee set up following the conference concluded that there were no good grounds for “prohibiting the use of ethyl gasoline” but suggested further investigations were necessary No funding for these investigations was approved by Congress Although evidence of the toxicity of lead accumulated through the 1930s and 1940s, TEL was safe from criticism Responding to a complaint from Ethyl Gasoline Corporation, manufacturer of TEL (and owned by General Motors and Standard Oil of New Jersey), the Federal Trade Commission (FTC) issued a restraining order preventing competitors from criticizing leaded gasoline in the commercial marketplace Ethyl gasoline, the FTC order read, “is entirely safe to the health of motorists and the public.” It was the passage of Clean Air Act legislation in 1970 that largely forced the demise of TEL The platinum used in catalytic converters is “poisoned” by lead Even then, Ethyl Corporation sued the EPA for denying a market for their product Ethyl claimed that the case against lead was not proven, despite the many studies on its toxicity Although a lower court upheld Ethyl’s claim, this decision was reversed by the U.S Court of Appeals In 1982, the then-administration’s Task Force on Regulatory Relief planned to relax or eliminate the lead phaseout, but under political and public pressure, the government reversed its opposition to lead phaseout By 1986, the primary phaseout of leaded gasoline in the United States was completed Thomas Midgley discovered both the chlorofluorocarbons and the role of TEL in improving gasolines The irony is that both discoveries were designed to make life better through progress in chemistry, yet both have had quite the opposite long-term effect Tetraethyllead poses both direct and indirect hazards The direct hazard has been to people working with gasoline, such as gas station attendants Because it has a low boiling point, the TEL added to gasoline vaporizes readily; hence, people exposed to TEL vapor absorb this neurotoxic lead compound through the lining of their lungs and develop headaches, tremors, and increasingly severe neurologic disorders The more widespread problem is the lead particulates in automobile exhausts In urban areas this is absorbed by the inhabitants’ lungs, whereas in rural areas near major highways, crops absorb lead and those consuming the crops will in turn experience increased 356 CHAPTER 14 • The Group 14 Elements lead intake A significant proportion of lead in the environment has come from the use of leaded gasoline To illustrate how the use of TEL has become a global issue, increased lead levels have even been found in the ice cap of Greenland Germany, Japan, and the former USSR were quick to outlaw TEL; other countries (such as the United States) followed more slowly One of the problems of eliminating TEL from gasolines was simply that modern vehicles need high-octane-rated gasoline Two solutions have been found: the development of the zeolite catalysts that enable oil companies to convert straight-chain molecules to the required branched-chain molecules and the addition of oxygenated compounds, such as ethanol, to fuels Thus, the need for octane boosters has been eliminated More and more countries around the world are phasing out TEL, but it will be many years before the planet will be TEL-free 14.22 Biological Aspects The Carbon Cycle There are many biogeochemical cycles on this planet The largest-scale process is the carbon cycle Of the 1016 tonnes of carbon, most of it is “locked away” in the Earth’s crust as carbonates, coal, and oil Only about 2.5 1012 tonnes are available as carbon dioxide Every year, about 15 percent of this total is absorbed by plants and algae in the process of photosynthesis, which uses energy from the Sun to synthesize complex molecules such as sucrose Some plants are eaten by animals (such as humans), and a part of the stored chemical energy is released during their decomposition to carbon dioxide and water These two products are returned to the atmosphere by the process of respiration However, the majority of the carbon dioxide incorporated into plants is returned to the atmosphere only after the death and subsequent decomposition of the plant organisms Another portion of the plant material is buried, thereby contributing to the soil humus or the formation of peat bogs The carbon cycle is partially balanced by the copious output of carbon dioxide by volcanoes The demand for energy has led to the burning of coal and oil, which were formed mainly in the Carboniferous era This combustion adds about 2.5 1010 tonnes of carbon dioxide to the atmosphere each year in addition to that from natural cycles Although we are just returning to the atmosphere carbon dioxide that came from there, we are doing so at a very rapid rate, and many scientists are concerned that the rate of return will overwhelm the Earth’s absorption mechanisms This topic is currently being studied in many laboratories The Essentiality of Silicon Silicon is the second most abundant element in the Earth’s crust, yet its biological role is limited by the low water solubility of its common forms, silicon dioxide and silicic acid, H4SiO4 At about neutral pH, silicic acid is uncharged and has a solubility of about 1023 mol?L21 As the pH increases, polysilicic acids predominate, then colloidal particles of hydrated silicon dioxide Although the solubility of silicic 14.22 acid is low, on the global scale it is enormous, with about 1011 tonnes of silicic acid entering the sea per year It is the continuous supply of silicic acid into the sea that enables marine organisms such as diatoms and radiolaria to construct their exoskeletons of hydrated silica On a smaller scale, plants require the absorption of about 600 L of water to form about kg of dry mass; thus, plants consist of about 0.15 percent silicon The silica is used by the plants to stiffen leaves and stalks In some plants, it is also used for defense (see the feature “Biomineralization” in Chapter 12) Farther up the food chain, herbivores ingest considerable amounts of silica A sheep consumes about 30 g of silicon per day, though almost all is excreted Humans are estimated to consume about 30 mg per day, about 60 percent from breakfast cereal and 20 percent from water and drinks It is the water-dissolved silicic acid that is bioavailable to our bodies The most convincing way to illustrate the essentiality of an element is to grow an organism in the total absence of that element This is a very difficult but not impossible task Studies with both rats and chicks showed that silicon-free diets resulted in stunted growth for both animals Addition of silicic acid to the diet rapidly restored natural growth The question obviously arose as to the function of the silicon Chemical studies showed that silicic acid did not react or bind with organic molecules Thus, incorporation into some essential biosynthetic pathway seemed highly unlikely The answer seems to lie with its inorganic chemistry As we saw in Chapter 13, Section 13.11, aluminum is ubiquitous in the environment and this element is highly toxic to organisms Addition of silicic acid to a saturated neutral solution of aluminum ion causes almost complete precipitation of the aluminum in the form of insoluble hydrated aluminosilicates Evidence that silicon did act in a preventative role was provided by a study of young salmon Those in water containing aluminum ion died within 48 hours Those in water containing the same concentration of aluminum plus silicic acid thrived It is now generally accepted that indeed silicon is essential to our diet to inhibit the toxicity of the naturally present aluminum in our foodstuffs Although silicon is an essential element, lung-absorbed silica is highly toxic We have already mentioned the hazards of asbestos It can cause two serious lung diseases: asbestosis and mesothelioma The dust of any silicate rock will also cause lung damage, in this case, silicosis The fundamental cause of the lung problems is due to the total insolubility of the silicates Once the particles stick in the lungs, they are there for life The irritation they cause produces scarring and immune responses that lead to the disease state The Toxicity of Tin Although the element and its simple inorganic compounds have a fairly low toxicity, its organometallic compounds are very toxic Compounds such as hydroxotributyltin, (C4H9)3SnOH, are effective against fungal infections in potatoes, grapevines, and rice plants For many years, organotin compounds were incorporated into the paints used on ships’ hulls The compound would kill the larvae of mollusks, such as barnacles, that tend to attach themselves to a ship’s hull, slowing the vessel considerably However, the organotin compound Biological Aspects 357 358 CHAPTER 14 • The Group 14 Elements slowly leaches into the surrounding waters, where, particularly within the confines of a harbor, it destroys other marine organisms For this reason, its marine use has been curtailed The Severe Hazard of Lead Why is there such concern about lead poisoning? For many elements the levels to which we are naturally exposed is many times smaller than toxic levels For lead, however, there is a relatively small safety margin between unavoidable ingestion from our food, water, and air and the level at which toxic symptoms become apparent Lead is ubiquitous in our environment Plants absorb lead from the soil, and water dissolves traces of lead compounds In addition to what our environment contains, humans have used lead products throughout history Although we no longer use “sugar of lead” as a sweetener, in more recent times lead from a number of other sources has become a hazard Basic lead carbonate, Pb3(CO3)2(OH)2, was one of the few easily obtainable white substances Thus, it was used until recently as a paint pigment, and many old houses have unacceptably high levels of lead resulting from the use of lead-based paints on the walls and ceilings The same compound was used by women as a cosmetic The factories producing the lead compound were known as “white cemeteries.” Working in such a plant was a last resort Yet circumstances of illness or death in the family or idleness or drunkenness by a husband gave some women little option even though it was a virtual death sentence Lead compounds were also used as ceramic glazes for cooking and eating vessels Thus lead(II) ion could leach out into the food being prepared The shift away from leaded gasolines has led to a drastic reduction in airborne lead particles, but lead is entering the environment from other sources The most commonly recognized source is the lead battery industry, which today constitutes about 85 percent of lead consumption The lead-acid battery is still the most efficient and cost-effective method of storing energy Lead is the most recycled element—particularly from defunct batteries The recycling process in the United States is generally carried out using extremely safe conditions with due safeguards for the workers and the environment However, such facilities are expensive to build and operate Much of the world’s lead is recycled in low-income countries, particularly in Asia, where safety and environmental concerns are lesser priorities With the cheapness of overseas recycling, much of the lead in the United States, Japan, and other developed countries is shipped to these Far Eastern recycling plants Although it is a very laudable aim to reduce poverty in such countries by bringing increased employment, in this specific example, the developed nations are exporting pollution About 95 percent of absorbed lead substitutes for calcium in the hydroxyapatite of bone This can be explained as the lead(II) ion is only slightly larger than and has a similar charge density to that of calcium Thus, the body “stores” lead In the bone, the half-life is about 25 years, so lead poisoning is a very long-term problem Lead interferes with the synthesis of hemoglobin and so can indirectly cause anemia At high concentrations, kidney failure, convulsions, brain damage, and then death ensue There is also strong evidence of Key Ideas neurological effects, including reduced IQ in children exposed to more than minimal lead levels As part of a program to minimize the hazard, playgrounds built on old industrial sites are checked for lead levels and, if necessary, closed or resurfaced 14.23 Element Reaction Flowcharts Flowcharts are shown for both carbon and silicon Na2C2 H2O HCOOH COCl2 H2SO4 Ni Ni(CO)4 CS2 O2 S Xs O2 O2 CO Cl2 CCl4 C Ca O2 Cl2 C2H2 O2 CO2 H2O CH4 Al4C3 H2 S Ca(OH)2 HCl NH3 CH3OH CaCO3 COS CO2 HCN Δ Ϫ OH H ϩ CNϪ Ca(HCO3)2 Na2SiO3 NaOH HCl SiHCl3 Δ Si C CH3Cl (CH3)2SiCl2 SiO2 HF C SiC Na2CO3 SiO44Ϫ Hϩ Si2O72Ϫ SiF62Ϫ KEY IDEAS • Carbon has an extensive chemistry resulting from its ability to catenate • There are three classes of carbides • The two oxides of carbon have very different properties • Silicates have a wide variety of structures • Tin and lead have weakly metallic properties 359 360 CHAPTER 14 • The Group 14 Elements EXERCISES 14.1 Write balanced chemical equations corresponding to the following chemical reactions: (a) solid lithium dicarbide(22) with water (b) silicon dioxide with carbon (c) copper(II) oxide heated with carbon monoxide (d) calcium hydroxide solution with carbon dioxide (two equations) (e) methane with molten sulfur (f) silicon dioxide with molten sodium carbonate (g) lead(IV) oxide with concentrated hydrochloric acid (two equations) 14.12 In compounds of carbon monoxide with metals, it is the carbon atom that acts as a Lewis base Show why this is expected using a formal charge representation of the carbon monoxide molecule 14.2 Write balanced chemical equations corresponding to the following chemical reactions: (a) solid beryllium carbide with water (b) carbon monoxide with dichlorine (c) hot magnesium metal with carbon dioxide (d) solid sodium carbonate with hydrochloric acid (e) heating barium carbonate (f) carbon disulfide gas and chlorine gas (g) tin(II) oxide with hydrochloric acid 14.15 Discuss the bonding in carbon disulfide in terms of hybridization theory 14.3 Define the following terms: (a) catenation; (b) aerogel; (c) ceramic; (d) silicone 14.4 Define the following terms: (a) glass; (b) molecular sieves; (c) cermet; (d) galena 14.13 Carbon dioxide has a negative enthalpy of formation, whereas that of carbon disulfide is positive Using bond energy data, construct a pair of enthalpy of formation diagrams and identify the reason(s) for such different values 14.14 Contrast the properties of carbon monoxide and carbon dioxide 14.16 From data tables in Appendix of DHUf and SU values, show that the combustion of methane is a spontaneous process 14.17 Explain why silane burns in contact with air, whereas methane requires a spark before it will combust 14.18 Describe why the CFCs were once thought to be ideal refrigerants 14.19 Why is HFC-134a a less than ideal replacement for CFC-12? 14.20 What would be the chemical formula of HFC-134b? 14.5 Contrast the properties of the three main allotropes of carbon—diamond, graphite, and C60 14.21 Why does methane represent a particular concern as a potential greenhouse gas? 14.6 Explain why (a) diamond has a very high thermal conductivity; (b) high pressure and temperature are required for the traditional method of diamond synthesis 14.22 Contrast the properties of carbon dioxide and silicon dioxide and explain these differences in terms of the bond types Suggest an explanation as to why the two oxides adopt such dissimilar bonding 14.7 Why are fullerenes soluble in many solvents even though both graphite and diamond are insoluble in all solvents? 14.8 Explain why catenation is common for carbon but not for silicon 14.9 Compare and contrast the three classes of carbides 14.23 The ion CO22 can be prepared using ultraviolet irradiation Whereas the carbon dioxide molecule is linear, this ion is V shaped, with a bond angle of about 127° Use an electron-dot diagram to aid your explanation Also, estimate an average carbon-oxygen bond order for the ion and contrast to that in the carbon dioxide molecule 14.10 Calcium carbide forms a NaCl structure with a density of 2.22 g?cm23 Assuming the carbide ion is spherical and taking the ionic radius of calcium as 114 pm, what is the radius of the carbide ion? 14.24 Draw the electron-dot diagram for the symmetrical cyanamide ion, CN222 Then deduce the bond angle in the ion 14.11 Write the chemical equation for the reaction used in the commercial production of silicon carbide Is it enthalpy or entropy driven? Explain your reasoning Calculate the values of DHU and DSU for the process to confirm your deduction, then calculate DGU at 2000°C 14.25 What geometry would you expect for the ion :C(CN)32? In fact, it is trigonal planar Construct one of the three resonance forms to depict the probable electron arrangement and deduce an average carbon-carbon bond order Beyond the Basics 14.26 Ultramarine, the beautiful blue pigment used in oil-based paints, has the formula Nax[Al6Si6O24]S2, where the sulfur is present as the disulfide ion, S222 Determine the value of x 14.27 In crocidolite, Na2Fe5(Si4O11)2(OH)2, how many of the iron ions must have a 21 charge and how many a 31 charge? 14.28 Describe the difference in structure between white asbestos and talc 14.29 Describe the major uses of zeolites 14.30 If the water in a zeolite is expelled by strong heating, must the absorption of water by the zeolite be an endo- or exothermic process? 14.31 What advantage of silicone polymers becomes a problem when they are used as breast implants? 361 14.35 To form the electrodes in the lead-acid battery, the cathode is produced by oxidizing lead(II) oxide to lead(IV) oxide, and the anode is produced by reducing the lead(II) oxide to lead metal Write half-equations to represent the two processes 14.36 Suggest the probable products formed when CaCS3 is heated 14.37 Write the formulas of two carbon-containing species that are isoelectronic with the C222 ion 14.38 There are two carbides that appear to contain the C42 ion What are they and how are they related? 14.39 Discuss why inorganic polymer chemistry is much less developed than organic polymer chemistry 14.32 Contrast the properties of the oxides of tin and lead 14.40 Discuss the introduction of tetraethyllead and why its use in gasoline continues today 14.33 Construct the electron-dot structures of tin(IV) chloride and gaseous tin(II) chloride Draw the corresponding molecular shapes 14.41 Write balanced chemical equations corresponding to each transformation in the element reaction flowcharts for carbon and silicon (page 359) 14.34 Lead(IV) fluoride melts at 600°C, whereas lead(IV) chloride melts at 215°C Interpret the values in relation to the probable bonding in the compounds BEYOND THE BASICS 14.42 Show from the standard reduction potentials from online Appendix that lead(IV) iodide would not be thermodynamically stable in aqueous solution 14.43 Our evidence that the Romans ingested high levels of lead(II) comes from examination of skeletons Suggest why the lead ions would be present in bone tissues 14.44 What are the main sources of lead in the environment today? 14.45 Conventional soda glass, when washed frequently in hot water, tends to become opaque and rough, while pure silica (SiO2) glass does not lose its brilliance Suggest an explanation 14.46 One route for the formation of the trace atmospheric gas carbonyl sulfide is hydrolysis of carbon disulfide Write a chemical equation for this reaction How would a water molecule attack a molecule of carbon disulfide? Draw a transition state for the attack, showing the bond polarities Thus, deduce a possible intermediate for the reaction and suggest why it is feasible 14.47 There is a trimeric silicate ion, Si3O962 (a) Draw a probable structure for the ion (b) Phosphorus forms an isoelectronic and isostructural ion What would be its formula? (c) Another element forms an isoelectronic and isostructural neutral compound What would be its formula? 14.48 Methyl isocyanate, H3CNCO, has a bent C¬N¬C bond, whereas silyl isocyanate, H3SiNCO, has a linear Si¬N¬C bond Suggest an explanation for the difference 14.49 In the following reaction, identify which is the Lewis acid and which the Lewis base Give your reasoning Cl2(aq) SnCl2(aq) S SnCl32(aq) 14.50 Tin reacts with both acids and bases With dilute nitric acid, the metal gives a solution of tin(II) nitrate and ammonium nitrate; with concentrated sulfuric acid, solid tin(II) sulfate and gaseous sulfur dioxide; with potassium hydroxide solution, a solution of potassium hexahydroxostannate(IV), K2Sn(OH)6, and hydrogen gas Write balanced net ionic equations for these reactions 14.51 Silicon dioxide is a weaker acid than carbon dioxide Write a balanced chemical equation to show how silicate 362 CHAPTER 14 • The Group 14 Elements rocks, such as Mg2SiO4, might, in the presence of “carbonic acid,” be a partial sink for atmospheric carbon dioxide 14.52 When aqueous solutions of aluminum ion and carbonate ion are mixed, a precipitate of aluminum hydroxide is formed Suggest an explanation using net ionic equations 14.53 A flammable gas (A) is reacted at high temperature with a molten yellow element (B) to give compounds (C) and (D) Compound (D) has the odor of rotten eggs Compound (C) reacts with a pale green gas (E) to give as a final product compound (F) and element (B) Compound (F) can also be produced by the direct reaction of (A) with (E) Identify each species and write balanced chemical equations for each step 14.54 Magnesium silicide, Mg2Si, reacts with hydronium ion to give magnesium ion and a reactive gas (X) A mass of 0.620 g of gas (X) occupied a volume of 244 mL at a temperature of 25°C and a pressure of 100 kPa The sample of gas decomposed in aqueous hydroxide ion solution to give 0.730 L of hydrogen gas and 1.200 g of silicon dioxide What is the molecular formula of (X)? Write a balanced chemical equation for the reaction of (X) with water 14.55 Tin(IV) chloride reacts with an excess of ethyl magnesium bromide, (C2H5)MgBr, to give two products, one of which is a liquid (Y) Compound (Y) contains only carbon, hydrogen, and tin 0.1935 g of (Y) was oxidized to give 0.1240 g of tin(IV) oxide Heating 1.41 g of (Y) with 0.52 g of tin(IV) chloride gives 1.93 g of liquid (Z) When 0.2240 g of (Z) was reacted with silver nitrate solution, 0.1332 g of silver chloride was formed Oxidation of 0.1865 g of (Z) gave 0.1164 g of tin(IV) oxide Deduce the empirical formulas of (Y) and (Z) Write a balanced chemical equation for the reaction of (Y) with tin(IV) chloride to give (Z) 14.56 The solid compound aluminum phosphate, AlPO4, adopts a quartz-like structure Suggest why this occurs 14.57 Use thermodynamic calculations to show that decomposition of calcium hydrogen carbonate is favored at 80°C: CaCO3(s) CO2(aq) H2O(l) Δ Ca(HCO3)2(aq) 14.58 Suggest why the density of moissanite is slightly less than that of diamond, even though the atomic mass of silicon is much greater than that of carbon 14.59 Use bond energy values to determine the energy available for transfer to a phosphor dye molecule when a mole of dicarbon tetroxide forms two moles of carbon dioxide 14.60 What is the oxidation number of each carbon atom in dicarbon tetroxide? ADDITIONAL RESOURCES For answers to odd-numbered questions: www.whfreeman.com/descriptive5e For accompanying video clips: www.whfreeman.com/descriptive5e ... Lake 250 11 .4 11 .5 11 .6 11 .7 11 .8 11 .9 252 255 256 257 259 2 61 Lithium Sodium Potassium Oxides Hydroxides Sodium Chloride Salt Substitutes 2 61 11. 10 11 .11 11 .12 11 .13 11 .14 262 262 264 264 Potassium... 370 15 .5 3 71 16 .15 16 .16 16 .17 16 .18 16 .19 16 .20 16 . 21 16.22 16 .23 16 .24 434 437 438 440 4 41 443 445 445 446 448 15 .3 Nitrogen Nitrogen Hydrides Haber and Scientific Morality 374 15 .6 15 .7 15 .8 15 .9... Ion 11 .15 Biological Aspects 11 .16 Element Reaction Flowcharts 265 265 266 The Group 13 Elements 2 91 13 .1 13.2 13 .3 292 293 294 Inorganic Fibers 295 13 .4 295 12 .1 12.2 12 .3 12 .4 12 .5 12 .6 12 .7