Appendix_A.fm Page 18 Friday, October 22, 2004 1:09 PM Elements Handbook Phase Diagram of Carbon 106 Group 4A Diamond(s) 105 104 Liquid 103 Physical Properties 102 Graphite(s) Pressure (atm) 101 • Group 4A elements are all Vapor 100 solids at room temperature. 0 2000 4000 6000 (The metallic properties of Temperature (C؇ • 2 Carbon | known since 6 4 Group 4A elements increase C ancient times Carbon from carbon to lead. 12.011 Graphite is more stable than diamond • Diamond, graphite, and at STP, but the activation energy is 2 Silicon | discovered in 14 8 buckminsterfullerene are too high for diamond to change to Si 4 1824 by Jöns Jacob three allotropes of carbon. graphite at these conditions. Silicon Berzelius 28.086 2 Melting and Boiling Points Density 32 8 Germanium | discovered 18 in 1886 by Clemens Ge 4 Germanium Winkler 4827 12 11.34 72.59 5000 bp ) 3 C) ؇ mp 2 4000 >3562* 9 50 8 Tin | known since 3280 7. 2 6 18 18 ancient times 2850 Sn 4 3000 2623 6 5.32 Tin 118.69 2000 1751 1420 3 2.27* 2.34 2 945 Density (g/cm 82 8 Lead | known since 1000 18 ( Temperature 232 327 32 ancient times 0 Pb 18 0 Lead 4 CSnPbSi Ge 207.2 CSnPbSi Ge *diamond *graphite Sources e/Photo Researchers • Carbon is found in nature as an element, y Al2SiO5 in Earth’s atmosphere as carbon dioxide, andalusite Cla in Earth’s crust as carbonate minerals, and M. in organic compounds produced in cells. y • Silicon can be produced by the reduction of silicon dioxide (silica) with magnesium, carbon, or aluminum. Example: ϩ ϩ SiO2(s) 2Mg(s) Si(s) 2MgO(s) ling Kindersle • Tin is prepared by reduction of the Schneider/ Photo Researchers mineral cassiterite, SnO2. k A. ylor/ Dor ϩ ϩ a SnO2(s) 2C(s) 2CO(g) Sn(s) Mar Fe2SiO4 AlSi2O5OH y T • Lead is refined from the mineral galena, olivine pyrophyllite Harr PbS. Galena is heated in air to form a About 90% of the minerals in Earth’s crust are mixture of PbO and PbSO4. Lead is silica and silicates. In silicates, each silicon produced through further reaction of atom is surrounded by three or four oxygen these compounds with PbS. atoms. These units can be linked together in chains, sheets, rings, or crystals. R18 Elements Handbook Appendix_A.fm Page 19 Monday, June 21, 2004 6:59 AM First Ionization Energy Electronegativity 1200 1086 3.0 2.5 Atomic Properties 900 786 761 1.9 708 715 2.0 1.8 1.8 1.8 • Group 4A elements have 600 1.0 an electron configuration 300 2 2 Energy (kJ/mol) that ends in ns np . Electronegativity 0 0 • For Group 4A elements, the CSnPbSi Ge C Si Ge Sn Pb most common oxidation numbers are ϩ4 and ϩ2. For Ϫ carbon, 4 is also common. CSiGeSnPb • Silicon and germanium are Atomic 77 109 122 139 175 radius (pm) semiconductors. Ionic 15 41 53 71 84 radius (pm) C4+ Si4+ Ge4+ Sn4+ Pb4+ 4Ϫ When carbon and silicon form four covalent bonds, there is often sp3hybridization. The result is compounds and ions with tetrahedral structures. methane molecule silicate ion Important Compounds and Reactions • Group 4A elements are oxidized by halogens. • Plants use carbon dioxide to produce Example: carbohydrates and oxygen. ϩ Ge(s) 2Cl2(g) GeCl4(l) • Aqueous sodium silicate, Na2SiO3, is used as • Group 4A elements combine with oxygen to an adhesive for paper, as a binder in cement, form oxides. Example: and to stabilize shale during oil drilling. ϩ ϩ SiO2(s) 2NaOH(aq) Sn(s) O2(g) SnO2(s) Na SiO (aq) ϩ H O(l) • Complete combustion of hydrocarbons yields 2 3 2 carbon dioxide and water. Example: • Acetylene is a fuel used for welding. It forms when calcium carbide and water react. CH (g) ϩ 2O (g) CO (g) ϩ 2H O(l) 4 2 2 2 ϩ ⌬ ϭ Ϫ CaC2(s) 2H2O(l) H 890 kJ/mol ϩ C2H2(g) Ca(OH)2(aq) • Tungsten carbide, WC, is used on the cutting surfaces of drill bits and saw blades. • Lead(IV) oxide, PbO2, is used as electrodes in lead acid car batteries. • Tin(II) fluoride, SnF2, is used in toothpaste to prevent tooth decay. Silicon dioxide, SiO2, is the sand on many beaches and is used to make glass. almer/CORBIS Group 4A R19 Gabe P Appendix_A.fm Page 20 Monday, June 21, 2004 6:59 AM Elements Handbook Group 4A C Green Chemistry The term green chemistry was coined in 1992. It describes the effort Decaffeinating Coffee to design chemical processes that don’t use or produce hazardous substances. The goal is to protect the environment and conserve Caffeine dissolves resources. For example, if a catalyst is used to reduce the temperature inside coffee beans at which a reaction occurs, the process requires less energy. soaked in water. Carbon dioxide is at the center of a green chemistry success story. Extraction Organic solvents are used to dissolve substances that are insoluble in water. Many of these solvents are toxic. It can be difficult to Caffeine diffuses into remove all traces of the toxic solvent from reaction products and supercritical CO2. safely recycle or dispose of the solvent. Supercritical carbon dioxide can replace some organic solvents. Absorption A gas becomes a supercritical fluid at a temperature and pressure called its critical point. For carbon dioxide, this occurs at 31.1ºC Water droplets leach caffeine from CO . and about 100 atmospheres. At its critical point, carbon dioxide 2 is in a hybrid state. It has a high density (like a liquid) but it is easily compressed (like a gas). Many organic compounds After the caffeine is extracted, the dissolve in supercritical carbon dioxide. The solvent is easily coffee beans are dried and roasted. separated from a reaction mixture because it evaporates at room The aqueous solution of caffeine is temperature and pressure. It is also used to separate substances sold to soft drink manufacturers. from mixtures. It can extract caffeine from coffee beans, dry- clean clothes, or clean circuit boards. ■ Si Optical Glass Glass is a material with the structure of a liquid, The glass used in eyeglasses, microscopes, but the hardness of a solid. In most solids, the and telescopes is called optical glass. It is particles are arranged in an orderly lattice. In purer than window glass and transmits more solid glass, the molecules remain disordered, light. Optical glass can be drawn into long as in a liquid. The main ingredient in most fibers that are used like tiny periscopes to glass is silica (SiO2), which is one of the few view tissues deep within the human body. substances that can cool without crystallizing. In an optical fiber, light travels through a thin glass center called the core. A second glass layer reflects light back into the core. An outer plastic layer protects the fiber from damage. When the fibers are bundled into cables, they often replace electrical cables in computer networks. They are also used to transmit television signals and phone calls over long distances. ■ R20 Elements Handbook Elizabeth Simpson/Getty Images Appendix_A.fm Page 21 Monday, June 21, 2004 6:59 AM Si Semiconductors C Beyond Buckyballs With a cellular phone, you can call your Buckminsterfullerene (C60) friends from almost any location. You can is one member of a family of play a video game, read e-mails, or get the fullerenes. These structures latest news. You may even be able to take are closed-cage spherical or and send digital photos. How can such a nearly spherical forms of complex device be small enough to fit in elemental carbon. The cages your pocket? Semiconductor technology are networks of 20 to 600 is responsible. carbon atoms. Silicon is a semiconductor. In its pure form, Scientists have verified the it conducts an electric current better than existence of nesting spheres most nonmetals but not as well as metals. of fullerenes. C60 can be But its ability to conduct can be changed nested inside C240, and this dramatically by doping, or adding traces pair can be nested inside C540. of other elements, to the silicon crystal. These nesting structures are sometimes called bucky- Doping with arsenic produces a donor, or onions because they resemble n-type, semiconductor. Each arsenic atom the layers of an onion. ■ has five valence electrons, compared with four for silicon. So there are extra electrons in the crystal. Doping with boron produces an acceptor, or p-type, semiconductor. Because boron has only three valence electrons, there is a positive “hole” in the crystal for every boron atom. The extra electrons or holes are free to move and conduct an electric current. Combinations of n-type and p-type semiconductors are used to build tiny electronic components. An integrated circuit containing millions of components can fit on a semiconductor wafer that is smaller than a fingernail! The resulting “chip” can control a computer, portable CD player, calculator, or cellular phone. ■ asieka/ Photo Researchers Alfred P Dr. Sumio Iijima discovered a tubular fullerene, or carbon nanotube, in Japan in 1991. aphs r ? Did You Know... A cell phone’s integrated One name for diamonds is “ice.” circuit must process more A diamond can quickly draw heat from and more data as features your hand when you touch it. Such a are added to the phone. high thermal conductivity is unusual for a substance containing covalent bonds. Daly/ Fundamental Photog . Group 4A R21 2003 Jeff J Appendix_A.fm Page 22 Friday, October 22, 2004 9:48 AM Elements Handbook Group 4A C Greenhouse Gases There are gases in Earth’s atmosphere that are The glass in a called greenhouse gases because they act like greenhouse the glass in a greenhouse.