新托福黄金阅读精选【文勇老师推荐】

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1、智课网TOEFL备考资料he"governingforthepeople","Nomattertheinterestsofthemasses"conceptunderstandingisnotinplace.Thespecificworktreatswiththedeployment,afewleadingcadrescomplainthatworkistoocomplicated,toomuchresponsibility,thepressureistoolarge,toomuchemphasisonthedi

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3、pmentofthePeriodicTableTheperiodictableisachartthatreflectstheperiodicrecurrenceofchemicalandphysicalpropertiesoftheelementswhentheelementsarearrangedinorderofincreasingatomicnumber(thenumberofprotonsinthenucleus).Itisamonumentalscientificachievement,anditsde

4、velopmentillustratestheessentialinterplaybetweenobservation,prediction,andtestingrequiredforscientificprogress.Inthe1800'sscientistsweresearchingfornewelements.Bythelate1860'smorethan60chemicalelementshadbeenidentified,andmuchwasknownabouttheirdescriptivechem

5、istry.Variousproposalswereputforthtoarrangetheelementsintogroupsbasedonsimilaritiesinchemicalandphysicalproperties.Thenextstepwastorecognizeaconnectionbetweengroupproperties(physicalorchemicalsimilarities)andatomicmass(themeasuredmassofanindividualatomofanele

6、ment).Whentheelementsknownatthetimewereorderedbyincreasingatomicmass,itwasfoundthatsuccessiveelementsbelongedtodifferentchemicalgroupsandthattheorderofthegroupsinthissequencewasfixedandrepeateditselfatregularintervals.Thuswhentheseriesofelementswaswrittensoas

7、tobeginanewhorizontalrowwitheachalkalimetal,elementsofthesamegroupswereautomaticallyassembledinverticalcolumnsinaperiodictableoftheelements.Thistablewastheforerunnerofthemoderntable.WhentheGermanchemistLotharMeyerand(independently)theRussianDmitryMendeleyevfi

8、rstintroducedtheperiodictablein1869-70,one-thirdofthenaturallyoccurringchemicalhe"governingforthepeople","Nomattertheinterestsofthemasses"conceptunderstandingisnotinplace.Thespecificworkt