1 / 77

I. L a w v s . T h eo r y

I. L a w v s . T h eo r y. Sc ie n t ifi c l a w = a g e n e r ali z a t i o n o f s ci e n t ifi c o b s e r v a t i o ns t h a t d e scr i b e s w h a t happ e ns ( d o e s n o t e xplain)

amelie
Download Presentation

I. L a w v s . T h eo r y

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. I.Lawvs.Theory Scientificlaw=ageneralizationofscientificobservationsthatdescribeswhathappens(doesnotexplain) Theory(model)=asetofassumptionsusedtoexplainobservationsandpredictnewobservations

  2. THEORY: Canneverbetrulyproven100%correct. Inevitablychange(andmustsometimesbeabandoned)asmoreinformationbecomesavailable. Consideredsuccessfulwhentheyexplainobservationsand,moreimportantly,predictnewobservations.

  3. AtomicStructure • EARLYATOMICTHEORY: • 400B.C-Democritus(Greekphilosopher) • •Coinedtheterm“atom”(meaningindivisible)todescribethesmallestparticlesofmatter • •Didnotexperiment

  4. 2)JOHNDALTON(EARLY1800’S): a)“FatheroftheModernAtomicTheory” b)Dalton’sAtomicTheoryhelpedexplainmeasurableobservationsandsuccessfullypredictnewobservations(whilestimulatingadditionalresearchfromDaltonandotherscientists).

  5. JohnDalton • AssumptionsofDalton’sAtomicTheory(proposedbyDaltonin1803): • Allmatteriscomposedofatoms • Allatomsofthesameelementareidenticalinsize,mass,otherproperties.Atomsofdifferentelementsdifferinsize,mass,andotherproperties.

  6. JohnDalton Atomscannotbesubdivided,created,ordestroyed Atomsofdifferentelementscombineinsimplewhole-numberratiostoformchemicalcompounds. Inchemicalreactions,atomsarecombined,separated,orrearranged.

  7. JohnDalton d)DaltonusedhisAtomicTheorytohelpcorrectlypredictnewobservationsleadingtothe“LawofMultipleProportions”.

  8. JohnDalton • LawofMultipleProportions=Themassesofoneelementthatcombinewithaconstantmassofanotherelementtoformmorethanonecompoundareintheratioofsmallwholenumbers • Carbonmonoxideandcarbondioxidecontainoxygenina1:2ratio. • 12gofcarbonreactswith16gofoxygentoformcarbonmonoxide,CO. • 12gofcarbonwillreactwith32gofoxygentoformcarbondioxide,CO2.

  9. JohnDalton f)Dalton’sAtomicTheoryexplainedmanyobservationsandcorrectlypredictedmanyadditionalobservations.ItDIDNOTcorrectlypredictallnewobservations(notheoryeverdoes).

  10. g)Dalton’sAtomicTheoryhasbeenmodified • toexplainthenewobservations: • Atomsofoneelementcanhavedifferent • masses(isotopes). • Atomscanbesubdivided(butnotinachemicalreactionorphysicalchange)…Nuclearreactions • Anatomofoneelementcanbechangedintoanatomofanotherelement(butnotinachemicalreactionorphysicalchange)……Nuclearreactions

  11. JohnDalton: g)Aswithalltheories,AtomicTheoryhasbeenchangedandexpandedovertime(andwillcontinuetochangeandexpand)toexplainnewobservations.

  12. 3)CATHODE-RAYTUBEEXPERIMENTS(late1800’s): • Cathode-raytube=Aglasstubecontainingagasataverylowpressurewhichcontainsanegativeelectrode(cathode)andapositiveelectrode(anode).Whenhighvoltageisapplied,a“cathoderay”passesfromthecathodetotheanodecausingthelowpressuregasinthetubetoglow(differentgasesglowdifferentcolors).

  13. 3)CATHODE-RAYTUBEEXPERIMENTS(late1800’s): • Earlycathode-raytubeexperiments: • Proposedthatacathoderayconsistsoftinyparticleswithmassandtheyarenegativelycharged.

  14. 3)CATHODE-RAYTUBEEXPERIMENTS(late1800’s): • J.J.Thomson–discoveredthe • electron • Usedearlycathode-raytubeexperimentsandsomeofhisownfindingstosupportthehypothesisthatelectronsarenegativelychargedparticles

  15. J.J.THOMSON: • Usedacathoderaytube-asvoltageacrossthetubewasincreased,abeamoflight(cathoderay)becamevisible • Cathoderay=beamofelectronsseenb/cofexcitedgas

  16. J.J.THOMSON: • Foundthatthebeamwasdeflectedbybothmagneticandelectricalfields • OBSERVATION: • Noticedthatthe“cathoderays”wereattractedtothepositiveelectrode,calledtheanode.

  17. WhatconclusionsdidThompsonhave? • Thecathoderaysweremadeupaverysmall • negativelychargedparticle–ELECTRONS

  18. J.J.THOMSON: • OBSERVATION:Measuredthebendingofthepathofthecathoderaysandwasabletodeterminingtheratioofanelectron’schargetoitsmass.Foundthattheratiowasalwaysthesame,regardlessofthemetalused

  19. WhatconclusionsdidThompsonhave? • Concludedthatthenegativelychargedparticlesweremuchlighterthanthelightestknowatom(hydrogen),whichmeantthatatomshadastructure!

  20. c)LaterProtonswerealsodiscoveredusingamodifiedcathode-raytubec)LaterProtonswerealsodiscoveredusingamodifiedcathode-raytube

  21. d)Thomson’sModeloftheAtom(PlumPuddingModel) • Thomsonpostulatedthatanatomconsistedofadiffusecloudofpositivechargewiththenegativeelectronsembeddedrandomlyinit. • ThisrepresentedamajorchangefromDalton’smodelofatomsasindivisible.

  22. Theexistenceoftheelectronraisednewquestions:ifelectronsarepartofallmatterandtheypossessanegativecharge,howcanallmatterbeneutral?Also,ifthemassofanelectronissosmall,whataccountsfortherestofthemassinatypicalatom?Theexistenceoftheelectronraisednewquestions:ifelectronsarepartofallmatterandtheypossessanegativecharge,howcanallmatterbeneutral?Also,ifthemassofanelectronissosmall,whataccountsfortherestofthemassinatypicalatom? • Moreexperimentstocome…

  23. 4)ERNESTRUTHERFORD&THEGOLD • FOILEXPERIMENT • RutherforddiscoveredtheNUCLEUSusingalphaparticles&goldfoil • Alphaparticle=arelativelylargepositivelychargedparticle

  24. ERNESTRUTHERFORD b)Gold-FoilExperiment(around1908-1909):Thingoldfoilwasbombardedbyalphaparticlesandthepathofthealphaparticleswaschartedaftertheypassedthroughthegoldfoil.

  25. ERNESTRUTHERFORD c)Expectedresults:Themassivealphaparticles(positivelycharged)wereexpectedto“crash”throughthegoldfoilwithlittleornodeflections;therewasnothinginThomson’smodeloftheatomtocauseanythingmorethanminordeflectionsofthealphaparticles.

  26. ERNESTRUTHERFORD • OBSERVATION:Somealphaparticlesweredeflectedatlargeangles,andsomewereredirectedbackward(surprisingresults!) • WhatconclusiondidRutherforddrawfromthisevidence? • ThePOSITIVEparticlesoftheatommustNOTbespreadoutevenly,butinsteadmustbeconcentratedatthecenteroftheatom-the(nucleus).

  27. ERNESTRUTHERFORD • OBSERVATION:Mostofthealphaparticlespassedthroughthegoldfoilwithfewdeflections. • WhatconclusiondidRutherforddrawfromthisevidence? • Mostofthealphaparticlesdidnothitanythingandpassedstraightthroughthegoldatomssotherefore,mostofthevolumeofanatomconsistsofemptyspace.

  28. ERNESTRUTHERFORD • f)Rutherford’sNuclearModel • Explainedtheneutralnatureofmatter:thepositivechargeofthenucleusbalancesthenegativechargeoftheelectrons.

  29. ERNSTRUTHERFORD • Suggestedthattheelectronstravelaround • thepositivelychargednucleus. • Theearlynuclearmodeldidnotaccountforalltheatom’smass • By1920,Rutherfordrefinedtheconceptofthenucleusandconcludedthatthenucleuscontainedpositivelychargedparticlescalledprotons.

  30. (a)Whenabeamofalphaparticlesisdirectedatathingoldfoil,mostparticlespassthroughthefoil undeflected,butasmallnumberaredeflectedatlargeanglesandafewbouncebacktowardtheparticle source.(b)Acloseupviewshows howmostofanatomis emptyspaceandonlythealphaparticlesthatstrike anucleusaredeflected.

  31. 5)JAMESCHADWICK(1932) a)Discoveredtheneutron

  32. 1)WHATISTHEDIFFERENCEBETWEENANATOMANDANELEMENT? Element=asubstancethatcannotbebrokendowntoothersubstancesbyachemicalreaction. Atom:thesmallestparticleofanelementthatcanexisteitheraloneorincombinationwithotheratoms.

  33. 2)3SUBATOMICPARTICLESOFANATOM

  34. 2)SUBATOMICPARTICLESOFANATOM • Subatomicparticle=aparticlesmallerthananatom • Ex:proton,neutron,electron

  35. 2)SUBATOMICPARTICLESOFANATOM b)Anatomiscomposedofsubatomicparticlesincludingprotons,neutrons,andelectrons(plusscientistshavedeterminedthatprotonsandneutronshavetheirownstructuresandtheyarecomposedofquarks-theseparticleswillnotbecoveredsincescientistsdonotyetunderstandiforhowtheyaffectchemicalbehavior).

  36. 2)SUBATOMICPARTICLESOFANATOM d)Protonsgivethenucleusthepositivecharge &determinestheidentityofanatom e)Protonsandneutronshaveaboutthesamemassandareover1840timesmoremassivethanelectrons.

  37. 2)SUBATOMICPARTICLESOFANATOM Mostofthemassofanatomislocatedinthenucleus(protons&neutrons).(Nuclearforcesholdtheparticlesofanucleustogether.Theseforcesonlyactoveraveryshortrange.) Atomsareelectricallyneutralb/cofthenumberofprotonsEQUALSthenumberofelectrons.

  38. 2)SUBATOMICPARTICLESOFANATOM • Nucleus=thepositivelycharged,densecentralportionofanatoms • Containsnearlyalloftheatom’smass,buttakesupaverysmallfractionofitsvolume

  39. 3)ATOMICNUMBER&AVERAGEATOMICMASS AtomicNumber 19 K Potassium 39.098 AverageAtomicMass • Atomicnumber:thenumberofprotonsinthenuclei • Alsorepresentsthenumberofelectronsthatanatomhassinceatomsareelectricallyneutral • Ex:AtomicnumberofNais11;Nahas11protonsand11electrons

  40. 3)ATOMICNUMBER&AVERAGEATOMICMASS • AverageAtomicMass:theweightedaverageoftheatomicmassesofnaturallyoccurringisotopesofanelement. • Isotopes=atomsofthesameelementwithdifferentnumberofNEUTRONS,therefore,differentmasses. • PeriodicTablelistsaverageatomicmass

  41. WeightedaveragesaccountforthepercentagesofeachisotopeofagivenelementWeightedaveragesaccountforthepercentagesofeachisotopeofagivenelement Importantb/ctheyindicaterelativemassrelationshipsinchemicalreactions

  42. 3)ATOMICNUMBER&AVERAGEATOMICMASS • Ex:Howaverageatomicmassiscalculated

  43. 4)ISOTOPES • Isotopes=atomsofthesameelementwithdifferentnumberofneutrons,therefore,differentmasses. • IsotopesofanelementallhavetheSAMENUMBERofprotonsandelectrons • Namedbytheirmassnumbers

  44. 4)ISOTOPES • Massnumber=thetotalnumberofprotonsandneutronsinthenucleusofanisotope. • MassNumber=#Protons+#Neutrons

  45. 4)ISOTOPES • Ex: H-3 H-1 H-2

More Related