Essen%alknowledgestandards•  1.B.1:Theatomiscomposedofnega%velychargedelectrons,whichcanleavetheatom,andapos%vielychargednucleusthatismadeofprotonsandneutrons.Thea?rac%onoftheelectronstothenucleusisthebasisofthestructureoftheatom.Coulomb’slawisqualita%velyusefulforunderstandingthestructureoftheatom.

•  4.A.3:Themagnitudeandtemperaturedependenceoftherateofreac%oniscontainedquan%ta%velyintherateconstant

FLT•  Iwillbeableto:– writenuclearequa%onsdemonstra%ngtheconserva%onofmassnumberandatomicnumbers– connectthehalf-lifeofareac%ontotherateconstantofafirst-orderreac%onandjus%fytheuseofthisrela%onintermsofthereac%onbeingafirst-orderreac%on

•  Bycomple1ngCh.19Notes

Ch.19:TheNucleus�AChemist’sView

Recall

Review–AtomicModels

Proton-NeutronModel

SubatomicPar%cles•  In1932,JamesChadwickdiscoveredtheneutron

•  Thiswasimportantinimprovingtheproton-electronatomicmodel

•  Newmodel:Theproton-neutronnucleus

Proton-NeutronModel

SubatomicPar%cles•  Wenowhavethreesubatomicpar%cles:– Protonsp+– Electronse-– Neutronsn0

•  Nucleons=subatomicpar%cleslocatedinthenucleusofatoms– Protonsandneutrons– Nucleonsarecomposedofsmallerpar%clescalledquarks

Review-Nuclide

NuclearStability

Forces•  Recall:Theelectromagne%cforce–  Electricallychargedpar%clescana?ractorrepeleachother

•  Whatwouldweexpecttooccurwithnucleons?

NuclearStability•  Notallnucleiarestable–  Posi%vely-chargedprotonscanrepeleachother

•  Thestrongnuclearforcebindsprotonsandneutronstogetherinthenucleus

NuclearStability•  StrongNuclearForce–  Thisforcecanonlyactoververyshortdistances–  Itisthestrongesta?rac%veforce(137%mesmorethanelectromagne%c)

– Overextremelyshortdistances,thestrongnuclearforceoverridestherepulsionoftheelectromagne%cforce

•  Lookingatthera%oofprotonstoneutronscanhelpusdeterminethestabilityofthenucleus

NuclearStability•  Allnuclideswithmorethan83protons(bismuth)areunstable

•  Lightnuclidesaremoststablewhentheneutron:protonra%ois1

•  Heaviernuclidesaremoststablewhentheneutron:protonra%oisgreaterthan1

ZoneofStability•  Areawherestablenuclidesresideasafunc%onofZand(A–Z)– Asthenumberofprotonsinthenuclideincreases,theneutron-to-protonra%orequiredforstabilityincreases

ZoneofStability

NuclearStability•  Certaincombina%onsofprotonsandneutronsseemtoconferspecialstability– Nuclideswithevennumbersofprotonsandneutronsaremorestablethanthosewithoddnumbers

•  Certainspecificnumbersofprotonsorneutronsproducestablenuclides

•  Magicnumbers–  Specialstabilityexistswhenthenumberofprotonsorneutronsis2,8,20,28,50,82,126

NuclearStability•  Unstablenucleiwithundergoradioac%vedecay•  Thenucleiwilldecomposetoformadifferentnucleus,formingoneormorepar%clesintheprocess•  Thetotalmassnumberandatomicnumbermustbeconservedinanynuclearchange

Pair-Share-Respond1.   Remindme�whatwasRutherford’satomic

model?

2.   HowdidChadwick’sdiscoverychangetheatomicmodel?

3.   DisFnguishbetweentheterms“subatomic

parFcles”and“nucleons”

4.   ExplaintherolesoftheelectromagneFc

forceandthestrongnuclearforceinthe

nucleus

5.   IdenFfysomepaPernsofnuclearstability26

Radioac%veDecay

Radioac%veDecay•  Unstablenuclei“decay”intonewnucleithroughthespontaneouschangeinnumberofprotons•  Ifthenumberofprotonschanges,isitthesameelementanymore?

Radioac%veDecay•  Radioac%vedecayoccurswhenaparentnucleusspontaneouslydecaysandformsadifferentnucleus,calledadaughternucleus

TypesofRadia%on

TypesofRadioac%veDecay

α-par%cleproduc%on

Spontaneousfission

β-par%cleproduc%on

Positronproduc%on

γ-rayproduc%on

TypesofRadia%on•  Alpha-Par%cleProduc%on– Alpha-par%cle(αpar%cle):Aheliumnucleus– Commonmodeofdecayforheavynuclides

TypesofRadia%on•  SpontaneousFission– Splijngofaheavynuclideintotwolighternuclideswithsimilarmassnumbers

– Occursatanextremelyslowrate

TypesofRadia%on•  Beta(β)-Par%cleProduc%on– Doesnotchangethemassnumber– Neteffect–tochangeaneutrontoaproton– Nuclidesthatlieabovethezoneofstablityareexpectedtobeβ-par%cleproducers

– Theemijngnucleusdoesnotcontainelectronseventhoughtheβpar%cleisanelectron

TypesofRadia%on•  Gammaray(γray):High-energyphoton•  γ-rayproduc%onaccompaniesnucleardecayandpar%clereac%ons

TypesofRadia%on•  PositronProduc%on•  Occursfornuclidesthatliebelowthezoneofstability– Thesenuclideshavesmallneutron/protonra%os

•  Positron–Par%clewiththesamemassasthee-butwithoppositecharge•  Neteffect–Tochangeaprotontoaneutron– Causestheproductnuclidetohaveahigherneutron/protonra%othantheoriginalnuclide

TypesofRadia%on•  Positron=an%par%cleofe-•  Annihila%on•  Whenapositroncollideswithanelectron,par%culatema?ertransformsintoelectromagne%cradia%onintheformofhigh-energyphotons

•  Characteris%cofma?er–an%ma?ercollisions

TypesofRadia%on•  ElectronCapture– Processbywhichthenucleuscapturesoneoftheinner-orbitalelectrons

– γraysarealwaysproducedtoreleaseexcessenergy

NuclearEqua%onsReview

NuclearEqua%onsReview•  Mustconservethemassnumber(total)andatomicnumber(total)

NuclearEqua%onsReview•  Writebalancedequa%onsforeachofthefollowingprocesses:

11 6 C produces a positron

214 83 Bi produces a particle β

237 93 Np produces an particle α

Solu%on(a)

Solu%on(b)

Solu%on(c)

DecaySeries

DecaySeries• Whenaradioac%venucleuscannotreachastablestateviaasingleradioac%vedecayprocess,adecayseriesoccursun%lastablenuclideisformed•  Examples

DecaySeries•  Insomecases,mul%pledecaysareneededtoproduceastablenuclide

DecaySeries

Prac%ce•  Iden%fythemissingpar%cleinthefollowingequa%on:

238 92 U He + ?→

24294Pu

242 90 Th234 90 Th234 92 U

Prac%ce•  Carbon-11isanunstableisotope.Whichkindofradioac%vedecaywouldbeexpectedforthisisotope?a.  Beta-par%cleproduc%onb.  Alpha-par%cleproduc%onc.  Positronproduc%on

Prac%ce•  ElectroncapturetransformsK-40intowhatnuclide?a.  Ca-40b.  Ar-40c.  He-4d.  K-40e.  Ca-39

Prac%ce•  WhentheU-235nuclideisstruckbyaneutron,theproductsaretwoneutrons,Ba-139,and:a.  Br-96b.  Kr-96c.  Rb-94d.  Kr-94e.  Sr-90