Nuclear ChemistryNuclear Chemistry

Unstable Nuclei and Radioactive Unstable Nuclei and Radioactive DecayDecay

Chemical and Nuclear ReactionsChemical and Nuclear Reactions

Chemical reactionsChemical reactions Nuclear reactionsNuclear reactions1. Bonds are broken and formed 1. Bonds are broken and formed on the e- level. p+ and non the e- level. p+ and n00 remain remain the samethe same

1. Nuclei emit particles and/or 1. Nuclei emit particles and/or raysrays

2. Atoms are unchanged, but can 2. Atoms are unchanged, but can be rearrangedbe rearranged

2. Atoms are converted into 2. Atoms are converted into atoms of other elements by atoms of other elements by releasing energyreleasing energy

3. Involve valence electrons only3. Involve valence electrons only 3. Can involve protons, neutrons, 3. Can involve protons, neutrons, and electronsand electrons

4. Small energy changes4. Small energy changes 4. Large energy changes – huge 4. Large energy changes – huge amounts of energy releasedamounts of energy released

5. Rxn rate influenced by 5. Rxn rate influenced by temperature, pressure, temperature, pressure, concentration, and catalystsconcentration, and catalysts

5. Rxn rate not normally affected 5. Rxn rate not normally affected by temperature, pressure, by temperature, pressure, concentration, or catalystsconcentration, or catalysts

RadioactivityRadioactivity

Chemical reactionChemical reaction involves only an involves only an atom’s electrons – the nucleus remains atom’s electrons – the nucleus remains unchangedunchanged

Nuclear reactionNuclear reaction involves a change in an involves a change in an atom’s nucleus (p+ or natom’s nucleus (p+ or n00 number) number)

RadioactivityRadioactivity is when substances is when substances spontaneously emit radiationspontaneously emit radiation

The rays and particles emitted are The rays and particles emitted are radiationradiation

RadioactivityRadioactivity

Radioactive atoms emit radiation because Radioactive atoms emit radiation because their nuclei are unstable (gain stability by their nuclei are unstable (gain stability by losing energy)losing energy)

Radioactive decayRadioactive decay is when atoms lose is when atoms lose energy by emitting radiation in a energy by emitting radiation in a spontaneous process. Atoms keep spontaneous process. Atoms keep decaying until they form stable, decaying until they form stable, nonradioactive atoms.nonradioactive atoms.

Types of RadiationTypes of Radiation

Alpha, beta, and gamma radiation have Alpha, beta, and gamma radiation have different amounts of electrical charge and different amounts of electrical charge and are affected differently by an electric fieldare affected differently by an electric field

Radioactive source, two plates (+,-), Radioactive source, two plates (+,-), stream of alpha, beta, and gamma raysstream of alpha, beta, and gamma rays

Alpha RadiationAlpha Radiation

2p2p++ and 2n and 2n00

Particles deflected to (-) plateParticles deflected to (-) plateExtra protons form new elementExtra protons form new elementNuclear equation:Nuclear equation:

2262268888Ra Ra → → 222222

8686Rn + Rn + 4422HeHe

radium-226radium-226 radon-222radon-222 alpha particlealpha particle

Beta RadiationBeta Radiation

Fast moving e-Fast moving e- -1 charge-1 chargeParticles deflected to (+) plateParticles deflected to (+) plateNuclear equation:Nuclear equation:

141466C C → → 1414

77N + N + 00-1-1ββ

carbon-14 nitrogen-14 beta particlecarbon-14 nitrogen-14 beta particle

Gamma RadiationGamma Radiation

High energy radiation without mass or electrical High energy radiation without mass or electrical chargecharge

Particles are not deflected by electric or Particles are not deflected by electric or magnetic fieldsmagnetic fields

Unable to form a new atom by themselves since Unable to form a new atom by themselves since they are mass-lessthey are mass-less

They accompany other types of radiation in They accompany other types of radiation in reactionsreactions 238238

9292U U →→ 2342349090Th + Th + 44

22He + 2He + 20000γγ

Uranium-238 thorium-234 alpha particle gamma raysUranium-238 thorium-234 alpha particle gamma rays

Characteristics of RadiationCharacteristics of Radiation

Radiation Radiation typetype

SymbolSymbol Mass Mass (amu)(amu)

ChargeCharge

AlphaAlpha 4422HeHe 44 2+2+

BetaBeta 00-1-1ββ 1/18401/1840 1-1-

GammaGamma 0000γγ 00 00

Penetrating PowerPenetrating Power

Human BodyHuman Body

Nuclear StabilityNuclear Stability

Elements > atomic number 83 are Elements > atomic number 83 are naturally radioactivenaturally radioactive

Ratio of pRatio of p++ to n to n00 determines the stability of determines the stability of an atoman atom

Atoms with too many or too few neutrons Atoms with too many or too few neutrons are unstableare unstable

Ratio of 1.5 : 1Ratio of 1.5 : 1

Fusion ReactionsFusion Reactions

Nuclear process in which Nuclear process in which two light nuclei two light nuclei combine to form a single heavier nucleuscombine to form a single heavier nucleus. . Examples: thermonuclear weapons and in Examples: thermonuclear weapons and in future nuclear reactorsfuture nuclear reactors

Fusion ReactionsFusion Reactions

The sum of the masses of the product The sum of the masses of the product nuclei is less than the sum of the masses nuclei is less than the sum of the masses of the initial fusing nuclei. of the initial fusing nuclei.

E=mcE=mc22, explains that the mass that is lost , explains that the mass that is lost it converted into energy carried away by it converted into energy carried away by the fusion products. the fusion products.

Fusion and our UniverseFusion and our Universe

Hydrogen isotopes collide in a star and fuse Hydrogen isotopes collide in a star and fuse forming a helium nucleus forming a helium nucleus

Lighter elements fuse and form heavier Lighter elements fuse and form heavier elements. These reactions continue until the elements. These reactions continue until the nuclei reach iron, the nucleus with the most nuclei reach iron, the nucleus with the most binding energy. No more fusion occurs in a star binding energy. No more fusion occurs in a star because it is energetically unfavorable to because it is energetically unfavorable to produce higher masses. Once a star has produce higher masses. Once a star has converted a large fraction of its core's mass to converted a large fraction of its core's mass to iron, it has almost reached the end of its life. iron, it has almost reached the end of its life.

Fission ReactionsFission Reactions

      Fission is a nuclear process in which Fission is a nuclear process in which a a heavy nucleus splits into two smaller heavy nucleus splits into two smaller nucleinuclei. An example of a fission reaction . An example of a fission reaction that was used in the first atomic bomb and that was used in the first atomic bomb and is still used in nuclear reactors is:is still used in nuclear reactors is:

235235U + n ----> U + n ----> 134134Xe + Xe + 100100Sr + 2nSr + 2n

FissionFissionReactionsReactions

Fission reactions can produce any combination Fission reactions can produce any combination of lighter nuclei so long as the number of protons of lighter nuclei so long as the number of protons and neutrons in the products sum up to those in and neutrons in the products sum up to those in the initial fissioning nucleus. As with fusion, a the initial fissioning nucleus. As with fusion, a great amount of energy can be released in great amount of energy can be released in fission because for heavy nuclei, the summed fission because for heavy nuclei, the summed masses of the lighter product nuclei is less than masses of the lighter product nuclei is less than the mass of the fissioning nucleus the mass of the fissioning nucleus

FissionFission

Fission is a process that has been occurring in Fission is a process that has been occurring in the universe for billions of years. We have not the universe for billions of years. We have not only used fission to produce energy for nuclear only used fission to produce energy for nuclear bombs, but we also use fission peacefully bombs, but we also use fission peacefully everyday to produce energy in nuclear power everyday to produce energy in nuclear power plantsplants

FissionFission

Nuclear energy is the most certain future Nuclear energy is the most certain future fuel source that we have. Currently in the fuel source that we have. Currently in the U.S. 107 nuclear reactors are producing U.S. 107 nuclear reactors are producing about 17% of our energy requirements. about 17% of our energy requirements. The U.S. Currently has plans of building The U.S. Currently has plans of building 42 more nuclear power plants in the next 42 more nuclear power plants in the next 20 years.20 years.

Downfalls to using Fission and Downfalls to using Fission and Fusion as fuel sources…Fusion as fuel sources…

Radioactive and toxic wastesRadioactive and toxic wastesFear/anxiety of terrorist bombingFear/anxiety of terrorist bombingSafe storage of toxic wastes?Safe storage of toxic wastes?Construction costs more than the energy it Construction costs more than the energy it

providesprovidesCoal still used and causing environmental Coal still used and causing environmental

issuesissuesCan cause health problems in humansCan cause health problems in humans

Practical Applications of Nuclear Practical Applications of Nuclear PowerPower

Cheap Cheap EfficientEfficientLower air pollutionLower air pollutionLower the price of electricityLower the price of electricityUranium is abundant on earthUranium is abundant on earth

Half LifeHalf Life

The time it takes for The time it takes for one-half of a one-half of a radioisotope’s nuclei radioisotope’s nuclei to decay into its to decay into its productsproducts

The half-life of The half-life of strontium-90 is 29 strontium-90 is 29 yearsyears

Number Number of half-of half-

liveslives

Elapsed Elapsed timetime

Amount presentAmount present

00 00 10 g10 g

11 29 yrs29 yrs 10 x (1/2)= 510 x (1/2)= 5

22 58 yrs58 yrs 10 x (1/2)10 x (1/2)(1/2)=2.5(1/2)=2.5

33 87 yrs87 yrs 10 X (1/2)(1/2)10 X (1/2)(1/2)(1/2)= 1.25(1/2)= 1.25

44 116 yrs116 yrs 10x(1/2)(1/2)(1/2)10x(1/2)(1/2)(1/2)

(1/2)=.625(1/2)=.625

Half LifeHalf Life

Amount remaining = (initial amount)(1/2)Amount remaining = (initial amount)(1/2)nn

n n = the number of half-lives that have passed= the number of half-lives that have passed

Radioactive Decay PracticeRadioactive Decay Practice

Practice Problem #1:Practice Problem #1:

If Gallium-68 has a half-live of 68.3 If Gallium-68 has a half-live of 68.3 minutes, how much of a 10.0 mg sample is minutes, how much of a 10.0 mg sample is left after one half-life? Two half-lives? left after one half-life? Two half-lives? Three half-lives?Three half-lives?

Radioactive Decay PracticeRadioactive Decay Practice

Practice Problem #2:Practice Problem #2:

If the passing of five half-lives leaves 25.0 mg If the passing of five half-lives leaves 25.0 mg of a strontium-90 sample, how much was of a strontium-90 sample, how much was present in the beginning?present in the beginning?