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1、OrganizationoftheElements:ThePeriodicTable,asweknowit,wasnotsomethingthatwas“stumbledupon.”Ithasbeendeveloped,modified,andimprovedforthelast200years.Bytheeighteenthcentury,chemistsrealizedthateachelementhadacharacteristicmass.Thus,theyusedmassastheirbasisfor
2、organizationoftheelements.In1817,JohannD?bereinerofGermanywasoneofthefirsttoformallyorganizetheelements.Hegroupedelementsinthreesbasedontheirsimilardifferencesinatomicmass.Hecalledthegroupsofthreetriads.Thesetriadshadsimilarchemicalandphysicalproperties.Ex-E
3、lementMassDMassProperties16.1lithium6.9Soft,16.1sodium23.0veryreactivepotassium39.1metals.44.4Ex-chlorine35.5Coloured,47.0bromine79.9veryreactiveiodine126.9non-metals.However,D?bereiner’s“LawofTriads”wasfoundtobemerelyacoincidence.By1829,80%oftheelementsknow
4、ndidnotfitintoatriad!ThenextmajordevelopmentinthePeriodicTablebeganin1864withtheBritishchemist,JohnNewlands.Hearrangedtheknownelementsinorderofincreasingatomicmass.Newlandsfoundthateveryeighthelementhadsimilarchemicalandphysicalproperties.Sincethepatternwasi
5、neights,Newlands’sdiscoverywascalledthe“LawofOctaves.”Unfortunately,thismethodoforganizationonlyworkedforthefirst20elements.Asmoreelementswerediscovered,theLawofOctavesfailedbecausethepropertiesbecameinconsistent.Forexample,thereactivemetalsLi,Na,K,Rb,andCsw
6、eregroupedwiththenon-reactivemetalsCu,Ag,andAu.Asaresultofthisfailure,improvementscameaboutveryrapidly.In1869,aRussianchemistDmitriMendeléevproposedthefollowinghypothesis,knownasMendeléev’sPeriodicLaw:“Thepropertiesoftheelementsareperiodicfunctionsoftheirrel
7、ativeatomicmasses.”Althoughhehadthislaw,Mendeléevdidnotrestricthimselftopatternsofeight;heincludedsub-groups.Mendeléevalsohadtheforesighttounderstandthatitwaspossiblesomeelementshadnotyetbeendiscovered.Soifhedecidedthatthenextheaviestelementdidnothavepropert
8、iesthatallowedittofitwithinthenextgroup,buthadpropertiesthatmadeitfitbetterinafollowinggroup,heleft“blanks.”Hedecidedthatelementsthatwouldfilltheblankswouldbediscoveredlater–HEWASRIGHT!Forexampl
