Nuclear Chemistry Nuclear Chemistry

Chapter 10Chapter 10

Alpha, Beta, and Gamma Alpha, Beta, and Gamma RaysRays

Radioactive elements emit three types of Radioactive elements emit three types of radiationradiation AlphaAlpha BetaBeta Gamma RaysGamma Rays

Alpha particlesAlpha particles AlphaAlpha particles carry a positive two charge particles carry a positive two charge

and are composed of 2 protons and 2 and are composed of 2 protons and 2 neutrons.neutrons. When an alpha particle is emitted, the atomic When an alpha particle is emitted, the atomic

mass will decrease by 4 AMU’s.mass will decrease by 4 AMU’s. The atomic # will decrease by 2.The atomic # will decrease by 2.

Beta particlesBeta particles Beta Beta particles carry a negative charge and particles carry a negative charge and

are high speed electrons.are high speed electrons. When a beta particle is emitted the atomic When a beta particle is emitted the atomic

mass will not change.mass will not change. The atomic # will increase by 1.The atomic # will increase by 1.

Gamma RaysGamma Rays Gamma Gamma radiation has no charge and is radiation has no charge and is

made of electromagnetic energy. made of electromagnetic energy. When a gamma radiation is emitted the When a gamma radiation is emitted the

atomic mass will not change.atomic mass will not change. The atomic # will not change.The atomic # will not change.

Penetrating Powers of Penetrating Powers of Nuclear RadiationNuclear Radiation Figure 4

Page 294

AlphaAlpha particles particles are 8,000 times as heavy as beta particles.are 8,000 times as heavy as beta particles.Paper or clothing will block alpha particlesPaper or clothing will block alpha particlesBeta Beta particles require a few sheets of aluminum foil.particles require a few sheets of aluminum foil.Gamma Gamma radiation is extremely dangerous--a thousand times radiation is extremely dangerous--a thousand times more potent than x-rays.more potent than x-rays. They will penetrate several They will penetrate several centimeters of solid lead.centimeters of solid lead.

End MondayEnd Monday

See Page 295 in Text.See Page 295 in Text.

Carbon-14 ProductionCarbon-14 Production

A free neutron enters nucleus and kicks out a proton. Nitrogen transmutates into carbon14.               0n1  +  7N14 --------->  6C14  + 1p1

Carbon-14 Decays by Beta Carbon-14 Decays by Beta EmissionEmission

The The betabeta particle is ejected from the particle is ejected from the nucleus.nucleus. The nucleon count (atomic mass) is The nucleon count (atomic mass) is

conserved. conserved. The atomic number increases by 1.The atomic number increases by 1.

Carbon14 transmutates into Nitrogen.

10.2 Rates of Nuclear 10.2 Rates of Nuclear DecayDecay

Interest GrabberInterest GrabberAnalogy for Half-LifeAnalogy for Half-LifeThe diagrams below represent the charge level of The diagrams below represent the charge level of a battery in a robotic dog at different times during a battery in a robotic dog at different times during the day. You charged the battery so that it was at the day. You charged the battery so that it was at its highest level at 9:00 A.M. Examine the its highest level at 9:00 A.M. Examine the diagrams, and then answer the questions that diagrams, and then answer the questions that follow.follow.

Section 10.2

Interest GrabberInterest Grabber1.1. The dog uses half of any remaining charge every 2 The dog uses half of any remaining charge every 2

hours. So, if the battery is fully charged at 9:00 A.M., then hours. So, if the battery is fully charged at 9:00 A.M., then the charge level will be half at 11:00 A.M., two hours later. the charge level will be half at 11:00 A.M., two hours later. If it uses half of the remaining charge another two hours If it uses half of the remaining charge another two hours later, what will the energy level be at 1:00 P.M.? later, what will the energy level be at 1:00 P.M.?

¼¼

Section 10.2

Interest GrabberInterest Grabber2.2. Given the same trend, what time is it when Given the same trend, what time is it when

the battery’s charge is at the level shown in the the battery’s charge is at the level shown in the last diagram?last diagram?

3:00 P.M.3:00 P.M.

Section 10.2

Interest GrabberInterest Grabber

3.3. The battery must be recharged when its The battery must be recharged when its charge level reaches half of the level shown in charge level reaches half of the level shown in the last diagram. What time will the battery need the last diagram. What time will the battery need to be recharged? to be recharged?

5:00 P.M.5:00 P.M.

Section 10.2

Half-LifeHalf-Life

The The half-lifehalf-life of a radioactive sample is average the of a radioactive sample is average the amount of time required for half of the sample to amount of time required for half of the sample to disintegrate (decay, disappear, transmute).disintegrate (decay, disappear, transmute).

Half-Half-liveslives are remarkably constant and not are remarkably constant and not affected by external conditions.affected by external conditions.

Nuclear Decay of Iodine-Nuclear Decay of Iodine-131131

Figure 7

24.21 24.21

daysdays

16.14 16.14

daysdays

8.07 8.07

daysdays

Half-LifeHalf-Life

Decay of 20.0 mg of Decay of 20.0 mg of 1515O. What remains after 3 half-lives? O. What remains after 3 half-lives? After 5 half-lives?After 5 half-lives?

Half-Life Half-Life 

A particular nucleus has A particular nucleus has a half life of 5 years.a half life of 5 years.

If there are 1000 nuclei If there are 1000 nuclei now, how many will now, how many will there be in 5 years?  there be in 5 years?  

In 10 years, 15 years?In 10 years, 15 years? Five years: 500 nuclei.Five years: 500 nuclei. Ten years: 250 nuclei.Ten years: 250 nuclei. 15 Years:125 nuclei.15 Years:125 nuclei.

Kinetics of Radioactive DecayKinetics of Radioactive DecayFor each duration (half-life), one half of the substance For each duration (half-life), one half of the substance

decomposes.decomposes.

For example: Ra-234 has a half-life of 3.6 daysFor example: Ra-234 has a half-life of 3.6 days

If you start with 50 grams of Ra-234If you start with 50 grams of Ra-234

After 3.6 days > 25 gramsAfter 3.6 days > 25 grams

After 7.2 days > 12.5 gramsAfter 7.2 days > 12.5 grams

After 10.8 days > 6.25 gramsAfter 10.8 days > 6.25 grams

Carbon-14 DatingCarbon-14 Dating The longer anything is dead, the less The longer anything is dead, the less

carbon 14 it will have in it. carbon 14 it will have in it. The half-life of carbon-14 is 5730 years.The half-life of carbon-14 is 5730 years.

1 Half life is 5730 years = ½1 Half life is 5730 years = ½ 2 Half life is 11460 years = ¼2 Half life is 11460 years = ¼ 3 Half life is 17190 years = 1/83 Half life is 17190 years = 1/8 4 Half life is 22920 years = 1/164 Half life is 22920 years = 1/16 5 Half life is 28650 years = 1/325 Half life is 28650 years = 1/32

Can only be use to date objects less Can only be use to date objects less than 50,000 years old.than 50,000 years old.

Measuring the Age of Organic Measuring the Age of Organic MatterMatter

A German tourist in A German tourist in the Italian Alps the Italian Alps discovered the discovered the remains of the remains of the "Iceman" in the ice "Iceman" in the ice of a glacier in 1991.of a glacier in 1991.

Calculating the Iceman's AgeCalculating the Iceman's Age

The current activity per The current activity per gram of carbon is half gram of carbon is half of what it would be if of what it would be if the Iceman were alive.the Iceman were alive.

Since the half-life of Since the half-life of carbon-14 is about carbon-14 is about 5730 years, the5730 years, theIceman's remains are Iceman's remains are about 5730 years old.about 5730 years old.

Uranium DatingUranium Dating The dating of older but nonliving things.The dating of older but nonliving things.

Rocks and mineralsRocks and minerals Uranium-238 decays with a half-life of 4.5 Uranium-238 decays with a half-life of 4.5

billion years, with an end-product ofbillion years, with an end-product oflead-206.lead-206.

By measuring  the lead-206 content, the age of By measuring  the lead-206 content, the age of rocks may be determined.rocks may be determined.

Interest GrabberInterest GrabberSection 10.3

Introduction to TransmutationIntroduction to TransmutationExamine the diagram below that represents the nuclei of isotopes in a Examine the diagram below that represents the nuclei of isotopes in a nuclear reaction, and answer the questions that follow. In the diagram, the nuclear reaction, and answer the questions that follow. In the diagram, the light circles represent protons, and the dark circles represent neutrons.light circles represent protons, and the dark circles represent neutrons.

1.1. What isotopes are represented by the starting nuclei? What isotopes are represented by the starting nuclei? 2.2. What isotope is represented by the larger nucleus that is produced in What isotope is represented by the larger nucleus that is produced in the nuclear reaction?the nuclear reaction?3.3. What other particle is produced? What other particle is produced?

Reading StrategyReading Strategy

Possible answers may include:Possible answers may include:a.a. Examples of artificial transmutationExamples of artificial transmutationb.b. Rutheford’s transmutation of nitrogenRutheford’s transmutation of nitrogen-14 into oxygen-17; the synthesis of -14 into oxygen-17; the synthesis of

neptunium-239neptunium-239c. Uses of transuranium elementsd. Smoke detectors (americium-241); space probes (plutonium-238)

Section 10.3

Monitoring Your UnderstandingMonitoring Your Understanding

Natural Transmutation of Elements

Total number of nucleons is conserved: Total number of nucleons is conserved:       238 =====> 234 + 4 238 =====> 234 + 4

Total charge is conserved:Total charge is conserved: 92 =====> 90 + 2 92 =====> 90 + 2

One nucleus changing into another.One nucleus changing into another.

Natural Transmutation of Elements

Total number of nucleons is conserved: Total number of nucleons is conserved:       234 =====> 234 + e234 =====> 234 + e--

Total charge is increased by 1:Total charge is increased by 1: 90 =====> 91 90 =====> 91

One nucleus changing into another.One nucleus changing into another.

Artificial Transmutation of Artificial Transmutation of ElementsElements

Ernest Rutherford was the first to cause Ernest Rutherford was the first to cause transmutation in the lab.transmutation in the lab.

The impact of an alpha particle on a The impact of an alpha particle on a nitrogen nucleus causes transmutation.nitrogen nucleus causes transmutation.

Reading StrategyReading StrategyComparing and ContrastingComparing and Contrasting

a. is the splitting of a large nucleus into two smaller fragments

b. is widely used as an alternative energy source

c. is the fusing of two small nuclei into one larger nucleus

d. is still being researched and developed as an alternativeenergy source

Comparing Strong Nuclear Comparing Strong Nuclear Forces and Electrical Forces and Electrical ForcesForces

Figure 15

Comparing Strong Comparing Strong Nuclear Forces and Nuclear Forces and Electrical ForcesElectrical Forces

Figure 15

Comparing Strong Comparing Strong Nuclear Forces and Nuclear Forces and Electrical ForcesElectrical Forces

Figure 15

Comparing Strong Comparing Strong Nuclear Forces and Nuclear Forces and Electrical ForcesElectrical Forces

Figure 15

Effect of Nuclear Size Effect of Nuclear Size on Nuclear and on Nuclear and Electrical ForcesElectrical Forces

Figure 16

Nuclear Fission of Uranium-Nuclear Fission of Uranium-235235

Figure 18

Chain Reaction of Uranium-Chain Reaction of Uranium-235235

Figure 19

The NucleusThe Nucleus

The nucleus is made of smaller subatomic particles The nucleus is made of smaller subatomic particles called nucleons or (called nucleons or (protons protons and and neutrons)neutrons).. The nucleus has a positive net charge.The nucleus has a positive net charge.

When an alpha particle leave they have a violent When an alpha particle leave they have a violent

electrical repulsion.electrical repulsion.

Nucleons are 2000 times more massive than an Nucleons are 2000 times more massive than an

electron.electron.

Unstable NucleiUnstable Nuclei Neutrons 1-4 provide strong Neutrons 1-4 provide strong

forces of attraction for the forces of attraction for the indicated proton, but other indicated proton, but other neutrons are too far away to neutrons are too far away to help balance the longer- range help balance the longer- range forces of repulsion provided by forces of repulsion provided by the many protons to the right of the many protons to the right of the proton.the proton.

The larger the nucleus, the more The larger the nucleus, the more unstable it is.unstable it is.

Reaching Stability Through Gamma Reaching Stability Through Gamma Ray EmissionRay Emission

Nuclei with excess energy emit gamma Nuclei with excess energy emit gamma rays to gain stability.rays to gain stability.

Nuclear FissionNuclear Fission The splitting of the nucleus of a heavy atom.The splitting of the nucleus of a heavy atom.

There is 100,000,000 times more There is 100,000,000 times more energy released from fission than when energy released from fission than when coal is burned.coal is burned.

A chain reactionA chain reaction A chain reaction occurs A chain reaction occurs

if more than one neutron if more than one neutron goes on to cause goes on to cause another fission.another fission.

One pound of U-235, ifOne pound of U-235, ifcompletely fissioned, completely fissioned, yields the same energy yields the same energy as 100,000,000 pounds as 100,000,000 pounds of coal.of coal.

Cadmium Control Rods Cadmium Control Rods Absorb NeutronsAbsorb Neutrons

Cadmium is a good absorber of neutrons.Cadmium is a good absorber of neutrons.

  A Nuclear ReactorA Nuclear Reactor Heat generated by fission in uranium Heat generated by fission in uranium

rods creates steam which turns turbinerods creates steam which turns turbineblades connected to a coil of wire in blades connected to a coil of wire in magnetic field.magnetic field.

Mass is Energy and Mass is Energy and Energy is MassEnergy is Mass

The work done per The work done per nucleon adds energy to nucleon adds energy to each nucleon, which each nucleon, which appears as increasedappears as increasedmass.mass.

Nucleons broken out of Nucleons broken out of the nucleus weigh more the nucleus weigh more outside than they do outside than they do inside.inside.

FusionFusion

Fusion Fusion is the opposite of is the opposite of fissionfission.. Energy in the sun come from hydrogen Energy in the sun come from hydrogen

fusion.fusion. Deuterium (hydrogen 2) must be moving Deuterium (hydrogen 2) must be moving

extremely fast to fuse.extremely fast to fuse.

Fusion in StarsFusion in Stars The extreme 10 The extreme 10

million degrees at million degrees at the core of the sun the core of the sun causes fusion of causes fusion of hydrogen into hydrogen into helium.helium.

Albert Einstein and Albert Einstein and Mass-Energy EquivalenceMass-Energy Equivalence

When a uranium When a uranium nucleus splits, the mass nucleus splits, the mass of the remnants is less of the remnants is less than the original mass. than the original mass. The difference appears The difference appears as light, heat, and as light, heat, and kinetic energy.kinetic energy.

        Albert Einstein         (1879-1955)

Mass is energy:  E = mc2    Energy is mass:  m = E /c2