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