Environmental Problems, Their Causes, and Sustainability 1

A PPENDIX 3SOME BASIC CHEMISTRYHow Can Elements Be Arranged in thePeriodic Table According to TheirChemical Properties? Chemists havedeveloped a way to classify the elementsaccording to their chemical behavior, inwhat is called the periodic table of elements(Figure 1). Each of the horizontal rows inthe table is called a period. Each vertical columnlists elements with similar chemicalproperties and is called a group.The partial periodic table in Figure 1shows how the elements can be classifiedas metals, nonmetals, and metalloids. Mostof the elements found to the left and atthe bottom of the table are metals, whichusually conduct electricity and heat andare shiny. Examples are sodium (Na), calcium(Ca), aluminum (Al), iron (Fe), lead(Pb), and mercury (Hg). Atoms of suchmetals achieve a more stable state by losingone or more of their electrons to form positivelycharged ions such as Na , Ca 2 ,and Al 3 .*Hydrogen, a nonmetal, is placed by itself abovethe center of the table because it does not fit verywell into any of the groups.Nonmetals, found in the upper right ofthe table, do not conduct electricity verywell and usually are not shiny. Examples arehydrogen (H),* carbon (C), nitrogen (N),oxygen (O), phosphorus (P), sulfur (S),chlorine (Cl), and fluorine (F). Atoms ofsome nonmetals such as chlorine, oxygen,and sulfur tend to gain one or more electronslost by metallic atoms to form negativelycharged ions such as O 2 ,S 2 , andCl . Atoms of nonmetals can also combinewith one another to form molecules inwhich they share one or more pairs of theirelectrons.The elements arranged in a diagonalstaircase pattern between the metals andnonmetals have a mixture of metallicand nonmetallic properties and are calledmetalloids. Figure 1 also identifies the elementsrequired as nutrients for all or someforms of life and elements that are moderatelyor highly toxic to all or most forms oflife. Six nonmetallic elements—carbon (C)oxygen (O), hydrogen (H), nitrogen (N),sulfur (S), and phosphorus (P)—make upabout 99% of the atoms of all living things.What Are Ionic and Covalent Bonds?Sodium chloride (NaCl) consists of athree-dimensional network of oppositelycharged ions (Na and Cl ) held togetherby the forces of attraction between oppositecharges (Figure 2). The strong forces ofattraction between such oppositelycharged ions are called ionic bonds. Becauseionic compounds consist of ions formedfrom atoms of metallic (positive ions) andnonmetallic (negative ions) elements,they can be described as metal-nonmetalcompounds.Figure 3 shows the chemical formulasand shapes of the molecules for severalGroupIA3Lilithium11Nasodium19K4Beberyllium12Mgmagnesium20Capotassium calcium37Rbrubidium55Cscesium38Srstrontium56IIABabarium21Scscandium39Yyttrium57LaAtomic numberSymbolName22Tititanium40Zrzirconium72Hflanthanium hafnium23V24Cr25Mn26Fevanadium chromium manganese iron41Nbniobium73Tatantalum42Mo43Tc44Ru27Cocobalt45Rhmolybdenum technetium ruthenium rhodium74WtungstenMetalsNonmetalsMetalloids75Rerhenium76Ososmium1HhydrogenIIIB IVB VB VIB VIIB VIIIB IB IIB77Irindium1Hhydrogen80Hgmercury28Ninickel46Pdpalladium78PtplatinumRequired forall or somelife-formsModeratelyto highlytoxic29Cucopper47Agsilver79Augold30Znzinc48Cdcadmium80HgmercuryIIIA IVA VA VIA VIIA5 6 7 8 9B C N O Fboron carbon13 14nitrogen oxygen fluorine15 16 17Al Si P S Claluminum silicon31 32phosphorus sulfur chlorine33 34 35Ga Ge As Se Brgallium germanium arsenic49 50 51selenium bromine52 53In Sn Sb Te Iindium tin antimony tellurium iodine81 82 83 84 85Ti Pb Bi Po Atthallium lead bismuth polonium astatineVIIIA2Hehelium10Neneon18Arargon36Krkrypton54Xexenon86RnradonFigure 1 Abbreviated periodic table of elements. Elements in the same vertical column, called agroup, have similar chemical properties. To simplify matters at this introductory level, only 72 of the115 known elements are shown.A8 APPENDIX 3