Related*Problems*from*Spring*2008*Final*Exam:*35*&*Spring*2009*Final*
Exam:*35* ... Comparison*of*Nuclear*Reactions*to*Chemical*Reactions". " 1.
Today’s(Topics!Nuclear(Chemistry"
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• Radioactive*decay*processes*(α,*β,*γ,*and*positron*emission;*electron*capture)* • Nuclear*stability*and*the*neutron:to:proton*ratio* • Kinetics*of*radioactive*decay*&*t1/2* • Mass*defect*&*nuclear*binding*energy* • Fusion*&*fission* • Nuclear*power* * * * Related*Problems*from*Spring*2008*Final*Exam:*35*&*Spring*2009*Final*Exam:*35* Corresponding*Connect*Problems:*5–16 * * Figures*taken*from$Chemistry,*4th*ed.*by*J.*McMurray*and*R.*C.*Fay,*Prentice:Hall,*2004.* All$materials$are$©$2012–2013$Lynmarie$A.$Posey$and$Michigan$State$University$unless$otherwise$noted;$ all$rights$reserved.$
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Learning(Objectives((Lecture(26)" You*should:* 1. understand*and*be*able*to*identify*the*five*decay*processes*(α,*β,*γ,*and*positron* emission;*electron*capture)*for*radionuclides*(radioactive*nuclei).* 2. recognize*the*differences*between*fission*and*fusion,*two*types*of*nuclear*reactions.* 3. be*able*to*balance*nuclear*reactions*for*radioactive*decay,*fission,*and*fusion.* 4. understand*the*relationship*between*the*neutron:to:proton*ratio*and*the*stability*of* nuclides/isotopes.* 5. know*the*types*of*radioactive*decay*observed*for*neutron:rich*and*proton:rich* nuclei.* 6. understand*that*radioactive*decay*is*a*first:order*kinetic*process*characterized*by* t1/2.* 7. be*able*to*calculate*the*mass*defect*of*a*nuclide*and*the*corresponding*nuclear* binding*energy.*
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Comparison*of*Nuclear*Reactions*to*Chemical*Reactions"
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1. Chemical*reactions*involve*rearrangement*of*valence:shell*electrons*(breaking* and/or*formation*of*chemical*bonds)*while*leaving*the*identity*of*the*participating* atoms*unchanged.*In*nuclear*reactions,*the*atom’s*nucleus*is*transformed,*often* changing*the*identity*of*the*atom.* 2. Changing*pressure*or*temperature*or*adding*a*catalyst*has*no*effect*on*nuclear* reactions.* 3. The*chemical*environment*(isolated*atom*vs.*atom*in*a*compound)*doesn’t*influence* the*outcome*of*a*nuclear*reaction.* 4. Energy*changes*in*nuclear*reactions*are*much*larger*(by*factors*>105).* 5. Isotopes*of*an*element*(same*atomic*number*but*different*mass*number)*exhibit*the* same*chemical*reactivity*but*different*nuclear*reactions.* *
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Isotopes' • Atoms*having*the*same*atomic*number*(#*of*protons)*but*different*mass*number** (#*of*nucleons*=*#*of*protons*+*#*of*neutrons).* • The*term*nuclide*refers*to*the*nucleus*of*a*particular*isotope.*Radionuclides*are* radioactive*nuclei.*
Example:" Consider*two*of*the*five*important*isotopes*of*iodine,* !"# !"! *(stable,*nonradioactive)* !"! and* !"! *(radioactive).*
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Nuclear(Chemistry"
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• Some*nuclei*are*radioactive,*and*they*decay*by*emission*of*radiation*(γ),*emission*of* particles*(α,*! ! ,*! ! ,*neutrons),*or*capture*of*electrons.* • Radioactive*decay*processes*follow*first:order*kinetics.* • All*elements*with*atomic*numbers*Z*>*83*are*radioactive.* • Nuclei*can*also*undergo*nuclear*transmutation*when*bombarded*by*protons,* neutrons,*or*other*nuclei.* • The*mass*number*and*atomic*number*are*conserved*in*nuclear*reactions.* Consequently,*balancing*equations*for*nuclear*reactions*requires*balancing*of*both* the*mass*number*and*the*atomic*number.*
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Nuclear((Radioactive)(Decay(Processes" 1. Alpha*(α)*Radiation* Emission*of*an*α*particle*( !! He*nucleus)*is*common*for*heavy*isotopes.* *
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!"# ! !"# !" Os → ! He + !" W*
When*balancing*nuclear*reactions,*it*is*only*necessary*to*worry*about*balancing* charges*on*the*elementary*particles.*It*is*not*necessary*to*worry*about*the*overall* !! charges*on*the*atoms*because*any*charged*atoms*formed,*such*as* !! He!! *and* !"# !" W * are*rapidly*neutralized.* 2. Beta*(β*or*! ! )*Radiation* A*neutron*spontaneously*decays*to*a*proton*and*an*electron*with*the*electron* (! ! = !!!! = !!!! )*being*emitted.*
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!"! !" Hf →
! !!!
+ !"! !" Ta*
Mass*number*does*not*change,*but*the*atomic*number*(#*of*protons)*increases*by*1.* *
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* 3. Gamma*(γ)*Radiation* Emission*of*high*energy/short*wavelength*(λ*=*10–11*–10–14*m)*radiation*often* accompanies*emission*of*α*and*β*particles.*Since*γ*radiation*has*no*mass,*it*is*often* omitted*in*the*balancing*of*nuclear*reactions*because*it*doesn’t*affect*the*mass* number*or*atomic*number.* 4. Positron*(! ! )*Emission* Conversion*of*a*proton*to*a*neutron*and*ejection*of*a*positron*(! ! = !!! = !!! ,*particle* with*the*same*mass*as*an*electron*but*opposite*charge)*results*in*no*change*in*mass* number*but*a*decrease*in*the*atomic*number*by*1.* *
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! !" !" ! F → ! ! + ! O*
5. Electron*capture* When*a*nucleus*captures*an*inner*shell/core*electron,*it*converts*a*proton*( !!!)*to*a* neutron*( !!!).*
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! !"# !"# !" Pb + !!! → !" Tl*
There*is*no*change*in*the*mass*number;*however,*the*number*of*protons*decreases* by*1,*and*a*new*element*is*formed.** "
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Example" Balance*the*following*nuclear*equations,*and*identify*the*particle*emitted.*
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!"# !"! !" Po → !" Pb+?*
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!" !" ! C → ! N+?*
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Nuclear(Stability"
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• Unstable*nuclei*decay*too*rapidly*for*rates*of*decay*and*half:lives*to*be*measured.* • Stable*nuclei*have*measurable*half:lives*and*decay*rates.* • Nonradioactive*nuclei*are*stable*indefinitely.* • Radioactive*nuclei*undergo*transformations*on*measurable*timescales.* What*distinguishes*nonradioactive*from*radioactive*nuclei?* • NeutronKtoKproton$ratio$determines$stability.*As*the*nuclear*mass*increases,*more* neutrons*are*needed*to*counteract*repulsion*between*protons.*Neutrons*play*a*role* in*binding*nucleons*together*to*form*the*nucleus.*As*Z*(atomic*number)*increases,* the*neutron:to:proton*ratio*required*for*stable*isotopes*increases.* • For*most*stable*isotopes,*the*ratio*of*neutrons*to*protons*>*1.*Only*elements*with** Z*
