Nuclear ChemistryNuclear Chemistry

RadioactivityRadioactivityRadioisotopes are unstable isotopes whose nuclei Radioisotopes are unstable isotopes whose nuclei gain stability by spontaneously undergoing changes. gain stability by spontaneously undergoing changes. These changes are accompanied by the emission of These changes are accompanied by the emission of large amounts of energy.large amounts of energy.Radioactive decay is the process by which materials Radioactive decay is the process by which materials give off this energy.give off this energy.The penetrating rays and particles that are emitted The penetrating rays and particles that are emitted during these changes are called radiation.during these changes are called radiation.Eventually unstable radioactive isotopes are Eventually unstable radioactive isotopes are transformed into stable isotopes of a different transformed into stable isotopes of a different element.element.

Radioactive IsotopesRadioactive Isotopes

All elements consist of at least one All elements consist of at least one radioactive isotope.radioactive isotope.Isotopes that have too many or too few Isotopes that have too many or too few neutrons (atomic mass larger or smaller neutrons (atomic mass larger or smaller than the average) tend to be radioactive.than the average) tend to be radioactive.All isotopes with an atomic number greater All isotopes with an atomic number greater than 83 are radioactive.than 83 are radioactive.

Identify the radioactive isotopeIdentify the radioactive isotope

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0% 1.1. 1111H H

2.2. 661414CC

3.3. 881616OO

4.4. 771414NN

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Identify the radioactive isotopeIdentify the radioactive isotope

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0% 1.1. Chlorine-35Chlorine-352.2. Carbon-12Carbon-123.3. Lead-207Lead-2074.4. Potassium-40Potassium-40

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Types of RadiationTypes of Radiation

Alpha radiationAlpha radiationBeta radiationBeta radiationGamma radiationGamma radiation

Alpha RadiationAlpha RadiationAlpha radiation consists of helium nuclei that are Alpha radiation consists of helium nuclei that are emitted from a radioactive isotope.emitted from a radioactive isotope.Alpha particles consist of two protons and two Alpha particles consist of two protons and two neutrons.neutrons.Alpha particles have a 2+ charge.Alpha particles have a 2+ charge.The symbol for an alpha particle is The symbol for an alpha particle is 44

22He or He or αα..Alpha particles are the most massive of the radioactive Alpha particles are the most massive of the radioactive particles (4 amu), the most damaging, and are the least particles (4 amu), the most damaging, and are the least penetrating (easily stopped by a piece of paper).penetrating (easily stopped by a piece of paper).http://phet.colorado.edu/en/simulation/alpha-decayhttp://phet.colorado.edu/en/simulation/alpha-decayhttp://www.hpwt.de/Kern2e.htm

What is the product when plutonium-What is the product when plutonium-238 undergoes alpha decay?238 undergoes alpha decay?

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0% 1.1. Uranium-234Uranium-2342.2. Thallium-206Thallium-2063.3. Lead-206Lead-2064.4. Radium-226Radium-226

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What is the product when What is the product when bismuth-210 undergoes alpha decay?bismuth-210 undergoes alpha decay?

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0% 1.1. Radium-226Radium-2262.2. Lead-206Lead-2063.3. Thallium-206Thallium-2064.4. Uranium-232Uranium-232

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What is the product when polonium-What is the product when polonium-210 undergoes alpha decay?210 undergoes alpha decay?

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0% 1.1. Bismuth-206Bismuth-2062.2. Lead-206Lead-2063.3. Radium-206Radium-2064.4. Thorium-206Thorium-206

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Beta ParticlesBeta ParticlesBeta particles consist of fast moving electrons formed Beta particles consist of fast moving electrons formed by the decomposition of a neutron in an atom.by the decomposition of a neutron in an atom.The neutron decomposes into a proton and an The neutron decomposes into a proton and an electron-the proton remains in the nucleus and the electron-the proton remains in the nucleus and the electron is emitted.electron is emitted.Beta particles have a 1- charge.Beta particles have a 1- charge.The symbol for a beta particle is The symbol for a beta particle is oo

-1-1e or e or ββ..Beta particles are 8000 x lighter than an alpha Beta particles are 8000 x lighter than an alpha particle, are less damaging, but are more penetrating particle, are less damaging, but are more penetrating (stopped by aluminum foil or thin pieces of wood).(stopped by aluminum foil or thin pieces of wood).http://phet.colorado.edu/en/simulation/beta-decay

What is the product when carbon-What is the product when carbon-14 undergoes beta decay?14 undergoes beta decay?

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0% 1.1. Carbon-13Carbon-132.2. Nitrogen-14Nitrogen-143.3. Oxygen-14Oxygen-144.4. Boron-10Boron-10

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What is the product when strontium-90 What is the product when strontium-90 undergoes beta decay?undergoes beta decay?

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0% 1.1. Rubidium-90Rubidium-902.2. Krypton-91Krypton-913.3. Strontium-91Strontium-914.4. Yttrium-90Yttrium-90

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What is the product when potassium-40 What is the product when potassium-40 undergoes beta decay?undergoes beta decay?

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0% 1.1. Calcium-40Calcium-402.2. Scandium-40Scandium-403.3. Argon-40Argon-404.4. Chlorine 40Chlorine 40

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Gamma RadiationGamma RadiationGamma radiation is high energy electromagnetic Gamma radiation is high energy electromagnetic radiation.radiation.Gamma rays are emitted along with alpha or Gamma rays are emitted along with alpha or beta particles.beta particles.Gamma rays have no mass or charge.Gamma rays have no mass or charge.The symbol for gamma rays is The symbol for gamma rays is oo

ooγγGamma rays are extremely penetrating and Gamma rays are extremely penetrating and potentially dangerous (stopped only by several potentially dangerous (stopped only by several meters of concrete or several centimeters of meters of concrete or several centimeters of lead).lead).

Nuclear Decay PuzzleNuclear Decay Puzzle

Uranium-238 is a radioactive isotope. Uranium-238 is a radioactive isotope. Through a series of 14 nuclear reactions, Through a series of 14 nuclear reactions, the unstable uranium isotope undergoes the unstable uranium isotope undergoes radioactive decay until it forms a more radioactive decay until it forms a more stable isotope of lead-206. stable isotope of lead-206.

Unstable isotopes formed during Unstable isotopes formed during the process:the process:

Uranium-234Uranium-234Thorium-234Thorium-234Thorium-230Thorium-230Protactinium-234Protactinium-234Radium-226Radium-226Radon-222Radon-222Polonium-218Polonium-218

Polonium-214Polonium-214Polonium-210Polonium-210Lead-214Lead-214Lead-210Lead-210Bismuth-214Bismuth-214Bismuth-210Bismuth-210

Radiation emitted during the Radiation emitted during the process:process:

Eight alpha particlesEight alpha particlesSix beta particlesSix beta particles

ProcedureProcedureWrite the isotope symbol for each of the Write the isotope symbol for each of the radioactive isotopes involved in the problem. radioactive isotopes involved in the problem. Put one symbol on each card. (There should be Put one symbol on each card. (There should be 15 total)15 total)On eight cards, write the symbol for alpha On eight cards, write the symbol for alpha radiation.radiation.On six cards, write the symbol for beta radiation.On six cards, write the symbol for beta radiation.Put the cards in the correct order to determine Put the cards in the correct order to determine the steps in going from uranium-238 to lead-206.the steps in going from uranium-238 to lead-206.After they are in the correct order, write the 14 After they are in the correct order, write the 14 nuclear equations that illustrate the steps.nuclear equations that illustrate the steps.

Radioactivity and Half-LivesRadioactivity and Half-Lives

Purpose: To simulate Purpose: To simulate the conversion of a the conversion of a radioactive isotope radioactive isotope over a period of time.over a period of time.Data:Data:

Trial #Trial # Number Number of atomsof atomsdecayeddecayed

Number of Number of atoms atoms remainingremaining

00 00 100100

AnalysisAnalysisUse graph paper and plot the “number of Use graph paper and plot the “number of isotopes remaining” (y-axis) vs. the trial number isotopes remaining” (y-axis) vs. the trial number (x-axis).(x-axis).Examine your graph. Is the number of isotopes Examine your graph. Is the number of isotopes remaining over time linear or nonlinear? Is the remaining over time linear or nonlinear? Is the rate constant over time or does it change?rate constant over time or does it change?By approximately how much did the number of By approximately how much did the number of isotopes remaining decrease with each trial?isotopes remaining decrease with each trial?Define half-life. What represented one half-life Define half-life. What represented one half-life during this lab?during this lab?Answer the “You’re the Chemist” questions on Answer the “You’re the Chemist” questions on page 852 in your textbook.page 852 in your textbook.

Half-LifeHalf-Life

A half-life is the time it takes for one -half A half-life is the time it takes for one -half of the nuclei of a sample of radioactive of the nuclei of a sample of radioactive isotopes to undergo radioactive decay.isotopes to undergo radioactive decay.Half-lives may be as short as a fraction of Half-lives may be as short as a fraction of a second or as long as billions of years.a second or as long as billions of years.

Half-lives of selected isotopesHalf-lives of selected isotopesIsotope Half-lifeHydrogen-3 12.3 years

Carbon-14 5730 years

Iodine-131 8.07 days

Lead-212 10.6 hours

Polonium-194 0.7 seconds

Polonium-210 138 days

Uranium-235 710 million years

Uranium-238 4.5 billion years

Plutonium-236 2.85 years

Graph the following dataGraph the following dataTime elapsed (days)Time elapsed (days) Amount of sample Amount of sample

remainingremaining00 100 g100 g

55 74 g74 g

1010 50 g50 g

1515 35 g35 g

2020 25 g25 g

2525 18 g18 g

3030 12.5 g12.5 g

Use the graph to answer the Use the graph to answer the following questions:following questions:

1. How much remains after 3 days?1. How much remains after 3 days?2.2. What is the half-life of this isotope?What is the half-life of this isotope?3.3. If 25 g remains, how much time has If 25 g remains, how much time has

elapsed?elapsed?4.4. How many half lives have occurred when How many half lives have occurred when

25 g remains?25 g remains?

The half-life of carbon-14 is 5700 years. If a 10 The half-life of carbon-14 is 5700 years. If a 10 gram sample undergoes decay for 17,100 years, gram sample undergoes decay for 17,100 years, how many half-lives has the sample undergone?how many half-lives has the sample undergone?

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0% 1.1. 10102.2. 553.3. 334.4. 11

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How much of the sample from the previous How much of the sample from the previous problems remains after 17,100 years?problems remains after 17,100 years?

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1.1. 10 g10 g2.2. 5 g5 g3.3. 2.5 g2.5 g4.4. 1.25 g1.25 g

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Cobalt-60 is a radioactive element used as a source of Cobalt-60 is a radioactive element used as a source of radiation in the treatment of cancer. Cobalt-60 has a half-radiation in the treatment of cancer. Cobalt-60 has a half-life of five years. If a hospital starts with a 1000-mg supply, life of five years. If a hospital starts with a 1000-mg supply, how much will remain after 10 years?how much will remain after 10 years?

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0% 1.1. 1000 mg1000 mg2.2. 750 mg750 mg3.3. 500 mg500 mg4.4. 250 mg250 mg

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If 62.5 g of the original sample of cobalt-60 If 62.5 g of the original sample of cobalt-60 remains, how much time has elapsed?remains, how much time has elapsed?

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1.1. 15 years15 years2.2. 20 years20 years3.3. 25 years25 years4.4. 30 years30 years

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Determining Half-LivesDetermining Half-LivesIn order to solve problems involving half-lives, In order to solve problems involving half-lives, the following equation may be used:the following equation may be used:

# of half-lives = total time/time of one half-live# of half-lives = total time/time of one half-live

To determine the amount of sample left, the following To determine the amount of sample left, the following equation may be used:equation may be used:

amount left = starting amount/ 2amount left = starting amount/ 2# of half-lives# of half-lives

Solve Practice Problems on page 849.Solve Practice Problems on page 849.

FissionFissionFission-when a large nucleus is bombarded with Fission-when a large nucleus is bombarded with neutrons, a division of the nucleus into 2 smaller neutrons, a division of the nucleus into 2 smaller nuclei occurs resulting in a large release of nuclei occurs resulting in a large release of energy.energy.

Example: Example:

• This energy is used in nuclear power This energy is used in nuclear power plants and in atomic bombs.plants and in atomic bombs.

FusionFusion

Fusion-nuclei with small masses combine Fusion-nuclei with small masses combine to form a nucleus with a larger mass. to form a nucleus with a larger mass.

Uses of FusionUses of Fusion

This type of reaction occurs in the sun and This type of reaction occurs in the sun and in hydrogen bombs. in hydrogen bombs. The high temperature needed to start a The high temperature needed to start a fusion reaction is produced by a fission fusion reaction is produced by a fission reaction.reaction.More energy is released per gram of More energy is released per gram of reactant in fusion than in fission.reactant in fusion than in fission.

Other Uses of Nuclear Other Uses of Nuclear ReactionsReactions

Dating of fossils (Carbon-14)Dating of fossils (Carbon-14)Dating of geological time (Potassium-40)Dating of geological time (Potassium-40)Industrial Uses (Radiation used to monitor Industrial Uses (Radiation used to monitor and control the thickness of aluminum foil and control the thickness of aluminum foil and plastic wrap)and plastic wrap)Nuclear imaging (MRI)Nuclear imaging (MRI)Food preservationFood preservationMedical applicationsMedical applications