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Task6
Whatisthedifferencebetweentodiscoverandtoinvent?Writeashortexplanation
oftheseterms.Beginyourexplanationasfollows:Todiscovermeans...
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whereastoinvent...
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SECTION2
DISCOVERYOFTHEPERIODICSYSTEM
8/1
Atendencytoclassifytheknownsubstanceshadbeenaroundsinceancienttimes.
Teclassificationwasbasedoncertainexternalphysicalfeaturesandoccasionallyon
thesitewhereasubstancewasfound.IntheMiddleAgesthealchemistsclassified
substancesonthebasisoftheirchemicalproperties.Causticsubstanceswereobtained
fromnon-causticsubstances,generallycalledsalts.Acidwasdistinguishedbytaste
andalkaliwasidentifiedbythefactthatacidspouredonitcausedeffervescence.
Fromthe17thtothe19thcenturiessubstancesweredividedaccordingtothefamilies
orkingdomsoftheiroriginintoamineral,plant,oranimalfamily.Inconsequence,
thesamechemicalcompound–asweknowtoday–butobtainedfromdifferent
sources,wassometimesregardedasadifferentsubstance.
Inthisperiodoftimemanyfamousscientists(RobertBoyle,TomasYoung,
AndréMarieAmpère,DanielRutherford,JędrzejŚniadecki,MikhailLomonosov,
andAntoineLaurentLavoisierwereamongthem)wereworkingontheclassification
oftheelements,butitwasDmitriMendeleevwhoon1stMarch,1869completedand
publishedhisPeriodicSystemoftheElements.MendeleevmodifiedhisSystemallhis
life,andinDecember1870hechangeditsarrangementfromverticaltohorizontal,
distinguishingaperiodofseventypicalelements–fromlithiumtofluoride–and
fiveperiods,eachofwhichcontainedtworowswithsevenelements,respectively.Tis
versionoftheperiodictableenabledtheauthortoachieveamoreaccuraterealization
oftheperiodicchangesofthepropertiesoftheelementsandtoformulatethelawof
periodicity.
Telawstates:
“Terearemutualrelationsbetweenthepropertiesoftheelementsandtheiratomic
weightswhichcanbeappliedtoalltheelements.Terelationshavetheformofaperiodic
function”.
TegreatsuccessofMendeleevwasalsoduetothefactthathepredictednotonly
atomicweightsbutalsosomephysicalandchemicalpropertiesoftheelementsand
theircompoundsunknowntohim.Hispredictionscametruewithinthefollowing
dozensofyears.
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