Nuclear ChemistryNuclear Chemistry

Two main forces in nucleusTwo main forces in nucleus

Strong nuclear force—all nuclear Strong nuclear force—all nuclear particles attract each otherparticles attract each other

Electric forces—protons repulse each Electric forces—protons repulse each otherother– Like charges repelLike charges repel

Key ScientistsKey Scientists

Henri BecquerelHenri Becquerel– X ray emission by uranium compoundsX ray emission by uranium compounds

Marie and Pierre CurieMarie and Pierre Curie– Discovered radium, poloniumDiscovered radium, polonium

Ernst RutherfordErnst Rutherford– Alpha particlesAlpha particles

What determines stability?What determines stability?

Balance between strong force Balance between strong force and electric forceand electric force

Neutron:proton ratio in Neutron:proton ratio in nucleusnucleus– Most stable between 1:1 and Most stable between 1:1 and

1.5:11.5:1

Binding energyBinding energy– Energy released when a nucleus Energy released when a nucleus

is formed from nucleonsis formed from nucleons

Unstable NucleiUnstable Nuclei

Most atoms have stable nuclei.Most atoms have stable nuclei. All elements with atomic number All elements with atomic number

≥84 are unstable.≥84 are unstable. Unstable nuclei (i.e., “radioactive” Unstable nuclei (i.e., “radioactive”

nuclei) undergo spontaneous change, nuclei) undergo spontaneous change, giving off energy or particles when giving off energy or particles when they change.they change.

Nuclear ReactionsNuclear Reactions

3 basic types3 basic types TransmutationTransmutation

– nucleus of one element is transformed nucleus of one element is transformed into nucleus of different elementinto nucleus of different element

Aka radioactive decay or nuclear decayAka radioactive decay or nuclear decay Nuclear reactions affect the nucleus of an atomNuclear reactions affect the nucleus of an atom

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More Nuclear ReactionsMore Nuclear Reactions

– Fission: a very heavy nucleus splits into Fission: a very heavy nucleus splits into two smaller nucleitwo smaller nuclei

– Fusion: two nuclei with small masses Fusion: two nuclei with small masses combine to form heaver, more stable combine to form heaver, more stable nucleinuclei

Particles in Nuclear DecayParticles in Nuclear Decay

3 main types3 main types– Alpha particlesAlpha particles

2 protons, 2 neutrons—a helium nucleus2 protons, 2 neutrons—a helium nucleus +2 nuclear charge+2 nuclear charge

– Cannot penetrate skin; dangerous if ingestedCannot penetrate skin; dangerous if ingested– Can be stopped by a piece of paperCan be stopped by a piece of paper

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Nuclear Particles, cont.Nuclear Particles, cont.

Beta particlesBeta particles An electron emitted from the nucleusAn electron emitted from the nucleus -1 charge-1 charge Symbol Symbol Fast moving, can penetrate into skinFast moving, can penetrate into skin Can be stopped by lead or glass Can be stopped by lead or glass

Gamma particlesGamma particles High energy electromagnetic waves emitted from High energy electromagnetic waves emitted from

nucleusnucleus No mass, no chargeNo mass, no charge SymbolSymbol Very penetrating; may not be stopped by several Very penetrating; may not be stopped by several

feet of concretefeet of concrete

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More Nuclear ParticlesMore Nuclear Particles

PositronsPositrons– Mass of electron, positive chargeMass of electron, positive charge

NeutronsNeutrons– 1 amu, no charge1 amu, no charge

ProtonsProtons– 1 amu, +1 charge1 amu, +1 charge

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Balancing Nuclear EquationsBalancing Nuclear Equations

Both mass and charge must be Both mass and charge must be conserved.conserved.– Sum of masses must be the same on Sum of masses must be the same on

both sides of arrow.both sides of arrow.– Sum of charges must be the same on Sum of charges must be the same on

both sides of arrow.both sides of arrow. Deduce the identity of the missing Deduce the identity of the missing

chemical species in the reaction.chemical species in the reaction.

Balancing a Nuclear ReactionBalancing a Nuclear Reaction

Uranium-238 spontaneously decays by Uranium-238 spontaneously decays by emitting an alpha particle.emitting an alpha particle.

Find mass of unknownFind mass of unknown Find atomic number of unknownFind atomic number of unknown Find symbol of unknownFind symbol of unknown

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