1492Ch28

Manahan,StanleyE.FUNDAMENTALSOFCHEMISTRYEnvironmentalChemistryBocaRaton:CRCPressLLC,200028FUNDAMENTALSOFCHEMISTRY____________________________________________________28.1.INTRODUCTIONThischapterisdesignedtogivethosereaderswhohavehadlittleexposuretochemistrythebasicknowledgeneededtounderstandthematerialintherestofthebook.Althoughitishelpfulforthereadertohavehadseveralcoursesinchemistry,includingorganicchemistryandquantitativechemicalanalysis,mostofthematerialinthisbookcanbeunderstoodwithless.Indeed,areaderwillingtodosomeinde-pendentstudyonthefundamentalsofchemistrycanunderstandmuchofthematerialinthisbookwithouteverhavinghadanyformalchemistrycoursework.Chapter28,“FundamentalsofChemistry,”canservetwopurposes.Forthereaderwhohashadnochemistry,itprovidestheconceptsandtermsbasictogeneralchemistry.Alargercategoryofreaderconsistsofthosewhohavehadatleastonechemistrycourse,butwhosechemistrybackground,forvariousreasons,isinadequate.Bylearningthematerialinthischapter,plusthesubjectmatterofChapter29,“FundamentalsofOrganicChemistry,”thesereaderscancomprehendtherestofthematerialinthebook.Foramorecompletecoverageofbasicchemistryreadersshouldconsultoneofanumberofbasicchemistrybooks,suchasFundamentalsofEnvironmentalChemistry1andothersupplementaryreferenceslistedattheendofthechapter.Chemistryisthescienceofmatter.Therefore,itdealswithallofthethingsthatsurroundhumankind,andwithallaspectsoftheenvironment.Chemicalpropertiesandprocessesarecentraltoenvironmentalscience.Avastvarietyofchemicalreactionsoccurinwater,forexample,includingacid-basereactions,precipitationreactions,andoxidation-reductionreactionslargelymediatedbymicroorganisms.Atmosphericchemicalphenomenaarelargelydeterminedbyphotochemicalprocessesandchainreactions.Alargenumberoforganicchemicalprocessesoccurintheatmosphere.Thegeosphere,includingsoil,isthesiteofmanychemicalprocesses,particularlythosethatinvolvesolids.Thebiosphereobviouslyiswherethemanybiochemicalprocessescrucialtotheenvironmentandtothetoxiceffectsofchemicalsoccur.©2000CRCPressLLCThischapteremphasizesseveralaspectsofchemistry.Itbeginswithadiscussionofthefundamentalsubatomicparticlesthatmakeupallmatter,andexplainshowtheseareassembledtoproduceatoms.Inturn,atomsjointogethertomakecom-pounds.Chemicalreactionsandchemicalequationsthatrepresentthemarediscussed.Solutionchemistryisespeciallyimportanttoaquaticchemistryandisaddressedinaseparatesection.Theimportant,vastdisciplineoforganicchemistryiscrucialtoallpartsoftheenvironmentandisaddressedinChapter29.28.2.ELEMENTSAllsubstancesarecomposedofonlyaboutahundredfundamentalkindsofmattercalledelements.Elements,themselves,maybeofenvironmentalconcern.The“heavymetals,”includinglead,cadmium,andmercury,arewellrecognizedastoxicsubstancesintheenvironment.Elementalformsofotherwiseessentialelementsmaybeverytoxicorcauseenvironmentaldamage.Oxygenintheformofozone,O3,istheagentmostcommonlyassociatedwithatmosphericsmogpollutionandisverytoxictoplantsandanimals.Elementalwhitephosphorusishighlyflammableandtoxic.Eachelementismadeupofverysmallentitiescalledatoms;allatomsofthesameelementbehaveidenticallychemically.Thestudyofchemistry,therefore,canlogicallybeginwithelementsandtheatomsofwhichtheyarecomposed.Eachelementisdesignatedbyanatomicnumber,aname,andachemicalsymbol,suchascarbon,C;potassium,K(foritsLatinnamekalium);orcadmium,Cd.Eachelementhasacharacteristicatomicmass(atomicweight),whichistheaveragemassofallatomsoftheelement.Atomicnumbersoftheelementsareintegralsrangingfrom1forhydrogen,H,tosomewhatmorethan100forsomeofthetransuranicelements(thosebeyonduranium).Atomicnumberisaunique,importantwayofdesignatingeachelement,anditisequaltothenumberofprotonsinthenucleiofeachatomoftheelement(seediscussionofsubatomicparticlesandatoms,below).SubatomicParticlesandAtomsFigure28.1representsanatomofdeuterium,aformofhydrogen.Itisseenthatsuchanatomismadeupofevensmallersubatomicparticles—positivelychargedprotons,negativelychargedelectrons,anduncharged(neutral)neutrons.SubatomicParticlesThesubatomicparticlesdifferinmassandcharge.Theirmassesareexpressedbytheatomicmassunit,u(alsocalledthedalton),whichisalsousedtoexpressthemassesofindividualatomsandmolecules(aggregatesofatoms).Theatomicmassunitisdefinedasamassequaltoexactly1/12thatofanatomofcarbon-12,theisotopeofcarbonthatcontains6protonsand6neutronsinitsnucleus.Theproton,p,hasamassof1.007277uandaunitchargeof+1.Thischargeisequalto1.6022x10-19coulombs,whereacoulombistheamountofelectricalchargeinvolvedinaflowofelectricalcurrentof1amperefor1second.Theneutron,n,hasnoelectricalchargeandamassof1.009665u.Theprotonandneu-©2000CRCPressLLC-+nElectron“cloud”NucleusFigure28.1.Representationofadeuteriumatom.Thenucleuscontainsoneproton(+)andoneneutron(n).Theelectron(-)isinconstant,rapidmotionaroundthenucleusformingacloudofnegativeelectricalcharge,thedensityofwhichdropsoffwithincreasingdistancefromthenucleus.troneachhaveamassofessentially1uandaresaidtohaveamassnumberof1.(Massnumberisausefulconceptexpressingthetotalnumberofprotonsandneutrons,aswellastheapproximatemass,ofanucleusors