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Chapter 21:Nuclear Chemistry

Date start: 1-19-2010Date Finished:

Your Name Period

Mr. Costein

Chapter 21: Nuclear Chapter 21: Nuclear ChemistryChemistry

This unit looks at the nature of radiation, Types of radiation and decay products, Radiation Units and exposure precautions Nuclear fission and fusion reactions Applications of

Nuclear Chemistry

The Geiger Counter

What does a Geiger Counter measure?

Radiation that can cause atoms to lose or gain electrons and become ionsions.

This type of radiation is called ionizing radiation.

There are two causes of background radiation:

Outer Space- Cosmic rays Natural decay from isotopes in the earth’s

crust/core

Daily Background Counts

DateDate Trial 1Trial 1 Trial 2Trial 2 AveragAveragee

Final Final CPMCPM

Historical Perspectives 1895: Wilhelm Roentgen discovers X-rays 1895: Wilhelm Roentgen discovers X-rays

and their effects.and their effects. 1896: Henri Becquerel discovers radioactive 1896: Henri Becquerel discovers radioactive

Uranium.Uranium. 1898: Pierre and Marie Curie discover two 1898: Pierre and Marie Curie discover two

new elements, polonium and radium.new elements, polonium and radium. 1905: Albert Einstein theory of relativity and 1905: Albert Einstein theory of relativity and

mass defect.mass defect. 1908: Hans Geiger creates an instrument to 1908: Hans Geiger creates an instrument to

measure ionizing radiation.measure ionizing radiation. 1934: Enrico Fermi proposes ‘transuranes” 1934: Enrico Fermi proposes ‘transuranes”

elements beyond uranium.elements beyond uranium. 1939: Lise Meitner , Otto Hahn and Fritz 1939: Lise Meitner , Otto Hahn and Fritz

Stassman explain nuclear fission. Stassman explain nuclear fission.

Nuclear Composition Nucleons are any particles found in the Nucleons are any particles found in the

nucleus, commonly they are protons and nucleus, commonly they are protons and neutrons.neutrons.

We would expect, the total mass of the We would expect, the total mass of the electrons, protons, and neutrons would be electrons, protons, and neutrons would be the mass of the atom, it is not, but rather it is the mass of the atom, it is not, but rather it is a smaller value.a smaller value.

Mass defectMass defect is the difference between the is the difference between the mass of an atom and the sum of the masses mass of an atom and the sum of the masses of its protons, neutrons and electrons.of its protons, neutrons and electrons.

Einstein explained this loss of mass as the Einstein explained this loss of mass as the result of the nucleus formation. Energy is result of the nucleus formation. Energy is given off from the conversion of matter to given off from the conversion of matter to energy (E=mcenergy (E=mc22 ). ).

This loss of mass from it’s conversion to This loss of mass from it’s conversion to energy provides nuclear stability.energy provides nuclear stability.

Nuclear Binding EnergyNuclear Binding Energy The energy released when a nucleus is The energy released when a nucleus is

formed from nucleons is called the formed from nucleons is called the nuclear nuclear binding energybinding energy..

This can be thought of the amount of energy This can be thought of the amount of energy to break a nucleus apart.to break a nucleus apart.

The higher the nuclear binding energy of a The higher the nuclear binding energy of a nuclide. the greater the nuclide stability.nuclide. the greater the nuclide stability.

The The binding energy per nucleonbinding energy per nucleon is the binding is the binding energy of the nucleus divided by the number energy of the nucleus divided by the number of nucleons(mass number) it contains.of nucleons(mass number) it contains.

Elements with intermediate atomic masses Elements with intermediate atomic masses (iron through lead) have the greatest binding (iron through lead) have the greatest binding energies (stability).energies (stability).

Nuclear Binding Example Problem

4He2

2 protons = 2 x 1.007276 = 2.014 552 amu2 neutrons = 2 x 1.008665 = 2.017 330 amu2 electrons = 2 x 0.0005486 = 0.001 097 amu Total mass combined = 4.032 979 amu

Measured mass = 4.002 602 amuMass Defect = 4.032979 – 4.002602 =

0.030377 amu

Nuclear Binding Page 2Mass Defect = 4.032979 – 4.002602 =

0.030377 amu

To convert amu to kg:1 amu = 1.6605 x 10-27 kg

0.030377amu X 1.6605 x 10-27 kg = 5.0441 x 10-29 kg

1 amu

Binding Energy = E = mc2

Nuclear Binding Page 3Binding Energy = E = mcBinding Energy = E = mc22

Mass = 5.0441 x 10-29 kgc = speed of light = 3.00 x 108 m/s

So E = (5.0441 x 10-29 kg)(3.00 x 108 m/s)2

E = 4.54 x 10-12 J per atomE = 6.022 x 1023 atoms/mol * 4.54 x 10-12 J per atomE= 2.733988 x 1012 J/mol (4 g of helium)

Nuclear StabilityNuclear Stability The neutron/proton ratio can be used to The neutron/proton ratio can be used to

predict nuclear stability.predict nuclear stability. For elements with low atomic numbers (1-For elements with low atomic numbers (1-

30) the nucleus is stable when there is a 30) the nucleus is stable when there is a 1:1 ratio.1:1 ratio.

For elements with a high atomic number For elements with a high atomic number (up to element 83), the nucleus is stable (up to element 83), the nucleus is stable when the ratio is 1.5:1.when the ratio is 1.5:1.

Elements having an atomic number greater Elements having an atomic number greater than 83 are unstable or radioactive.than 83 are unstable or radioactive.

Stable nuclei tend to have even numbers Stable nuclei tend to have even numbers of nucleons in their nucleus. of nucleons in their nucleus.

N/P RatioN/P Ratio

Nuclear Shell ModelNuclear Shell Model Stable nuclei tend to have even numbers of Stable nuclei tend to have even numbers of

nucleons in their nucleus. (protons, neutrons nucleons in their nucleus. (protons, neutrons or total nucleons) or total nucleons)

The most stable atoms have 2, 8, 20, 28, 50, The most stable atoms have 2, 8, 20, 28, 50, 82 or 126 protons, neutrons, or total nucleons.82 or 126 protons, neutrons, or total nucleons.

The nuclear shell theory states that nucleons The nuclear shell theory states that nucleons exists in different energy levels, or shells, in exists in different energy levels, or shells, in the nucleus. Completed nuclear energy levels the nucleus. Completed nuclear energy levels are those with 2, 8, 20, 28, 50, 82 and 126 are those with 2, 8, 20, 28, 50, 82 and 126 nucleons.nucleons.

These numbers are sometimes called the These numbers are sometimes called the ““magic numbers”magic numbers” for nuclear stability. for nuclear stability.

If both the protons and neutrons are equal to If both the protons and neutrons are equal to the magic numbers, these are called the the magic numbers, these are called the ““double magic numbersdouble magic numbers” and have the ” and have the greatest stability.greatest stability.

Nuclear Shell Model Nuclear Shell Model ExamplesExamples

The most stable atoms have 2, 8, The most stable atoms have 2, 8, 20, 28, 50, 82 or 126 protons, 20, 28, 50, 82 or 126 protons, neutrons, or total nucleons.neutrons, or total nucleons.

Examples of stable nuclidesExamples of stable nuclides 40 40 CaCa

2020

16 16 OO 88

28 28 SiSi 1414

Nuclear Reactions and Nuclear Reactions and terms:terms:4 types of Nuclear Reactions:4 types of Nuclear Reactions:

Radioactive decayRadioactive decay refers to the emission of refers to the emission of an alpha particle, a beta particle, or gamma an alpha particle, a beta particle, or gamma ray and the ray and the formation of a slightly lighter formation of a slightly lighter and more stable nucleusand more stable nucleus..

Nuclear disintegration Nuclear disintegration is when an unstable is when an unstable nuclei from nuclear bombardment nuclei from nuclear bombardment emits a emits a proton or neutronproton or neutron and becomes more and becomes more stable.stable.

FissionFission refers to the process in which a very refers to the process in which a very heavy nucleus splitsheavy nucleus splits to form two or more to form two or more medium-mass nuclei.medium-mass nuclei.

FusionFusion refers to the process in which refers to the process in which lightweight lightweight nuclei combinenuclei combine to form heavier to form heavier more stable nuclei.more stable nuclei.

Other Nuclear Terms:Other Nuclear Terms: Transmutation Transmutation is the changeis the change in the identity in the identity

of a nucleus as a result of a change in the of a nucleus as a result of a change in the number of protons.number of protons.

Radioactive decay Radioactive decay is spontaneous is spontaneous disintegration of a nucleus into slightly lighter disintegration of a nucleus into slightly lighter and more stable nucleus, accompanied by the and more stable nucleus, accompanied by the emission of particles, electromagnetic radiation emission of particles, electromagnetic radiation or both.or both.

RadiationRadiation- the process of emitting or releasing - the process of emitting or releasing waves of energy, such as light, x-rays, or other waves of energy, such as light, x-rays, or other types of electromagnetic waves.types of electromagnetic waves.

RadioactivityRadioactivity is the property of some is the property of some elements to spontaneously emit alpha or beta elements to spontaneously emit alpha or beta particles with gamma rays by the disintegration particles with gamma rays by the disintegration of the nuclei.of the nuclei.

Properties of Radioactive Properties of Radioactive Nuclides:Nuclides:

They expose light sensitive emulsions. They expose light sensitive emulsions. (Roentgen, 1895)(Roentgen, 1895)

They fluoresce or glow with certain compounds. They fluoresce or glow with certain compounds.

(Curie, 1898)(Curie, 1898) They produce “charged” or ionized gas They produce “charged” or ionized gas

particles. particles. (Geiger, 1908)(Geiger, 1908)

Exposure to radio-nuclides can cause harmful Exposure to radio-nuclides can cause harmful physiological effects leading to death.physiological effects leading to death.

They undergo radioactive decay and have a They undergo radioactive decay and have a half-life.half-life.

Half-Life of a Radioisotope

Half-lifeHalf-life is the time it required for half is the time it required for half the atoms of a radioactive nuclide to the atoms of a radioactive nuclide to decay. It can be measured in seconds, decay. It can be measured in seconds, minutes, days, or years.minutes, days, or years.

decay curve

8 mg 4 mg 2 mg 1 mg

initial

1 half-life 2 3

Examples of Half-Life

IsotopeIsotope Half lifeHalf lifeC-15C-15 2.4 sec2.4 secK-42K-42 12.36 hours 12.36 hours Na-24Na-24 15 hours15 hoursRa-224Ra-224 3.6 days3.6 daysRa-223Ra-223 12 days12 daysI-125I-125 60 days60 daysC-14C-14 5700 years5700 yearsU-235U-235 710 000 000 years710 000 000 years

Half-Life ProblemRa-223 has a half-life of 12 days. If Ra-223 has a half-life of 12 days. If

today, you had 100 grams of this today, you had 100 grams of this isotope, how much would remain after isotope, how much would remain after 36 days?36 days?

1.1. How many half-life periods has it undergone in 36 days?How many half-life periods has it undergone in 36 days?

36 days36 days = 3 half life periods = 3 half life periods 12 days/half-life 12 days/half-life

100 g 50g 25g 12.5 g

Types of Radioactive Types of Radioactive DecayDecay

Alpha EmissionAlpha EmissionBeta EmissionBeta Emission

Positron EmissionPositron EmissionElectron CaptureElectron CaptureGamma EmissionGamma Emission

Comparing Nuclide Comparing Nuclide EmissionsEmissions

Decay Models

Graphic shows U-238 with an alpha and one beta decays.Graphic shows U-238 with an alpha and one beta decays.

Protactinium atomic number 91 is formed.Protactinium atomic number 91 is formed.

Alpha and Beta DecayAlpha and Beta Decay

Alpha decayAlpha decay

Beta DecayBeta Decay

Key points in Balancing Nuclear Equations

1. Most decay products reduce the decaying atom’s atomic mass or atomic number or both.

2. The beta particle is the exception, when it is a decay product, the atomic number of the decaying atom increases by one.

3. Gamma ray emission by a decaying atom does NOT change the atomic mass or atomic number of the atom.

Nuclear Equation Problem

Example Nuclear Reactions

226 Ra 226 Ac + ________ 88 89

226 Pu 4 He + ________ 94 2

235 U 235 Pa + ________ 92 91

Alpha EmissionAlpha Emission consists of a Helium nucleus with no consists of a Helium nucleus with no

electrons.electrons. has 2 protons and 2 neutrons.has 2 protons and 2 neutrons. has a +2 chargehas a +2 charge has an atomic mass of 4has an atomic mass of 4 has a speed that is 1/10 the speed of has a speed that is 1/10 the speed of

light.light. can be stopped by a piece of paper, can be stopped by a piece of paper,

cloth, or skin.cloth, or skin.

The symbol is the Greek letter alphaThe symbol is the Greek letter alpha

particle or particle or 4 4

2 2 HeHe

Beta EmissionBeta Emission is a stream of negatively charged is a stream of negatively charged

electrons.electrons. has a very light mass of an electronhas a very light mass of an electron has a -1 chargehas a -1 charge can be stopped by a piece of aluminumcan be stopped by a piece of aluminum has a speed that is 90% of the speed of has a speed that is 90% of the speed of

light.light. can ionize air and other particles.can ionize air and other particles. The symbol is the Greek letter, betaThe symbol is the Greek letter, beta

particle or particle or 0 0

-1 -1 ee

Positron EmissionPositron Emission is a stream of positively charged is a stream of positively charged

electrons.electrons. has a very light mass of an electronhas a very light mass of an electron has a +1 charge has a +1 charge (change this in notes)(change this in notes) can be stopped by a piece of aluminumcan be stopped by a piece of aluminum has a speed that is 90% of the speed of has a speed that is 90% of the speed of

light.light. can ionize air and other particles.can ionize air and other particles. The symbol is the Greek letter, betaThe symbol is the Greek letter, beta

particle or oparticle or o

+1 +1 ee

Electron CaptureElectron Capture

is a capture of an inner orbital is a capture of an inner orbital electron by the nucleus.electron by the nucleus.

has a very light mass of an electron.has a very light mass of an electron. has a -1 charge.has a -1 charge. results in a combination of an electron results in a combination of an electron

and a proton to form a neutron.and a proton to form a neutron.

The symbol on the reaction side of a The symbol on the reaction side of a nuclear reaction is onuclear reaction is o

-1 -1 ee

Gamma EmissionGamma Emission is form of energy or electromagnetic is form of energy or electromagnetic

radiation.radiation. has an extremely short wavelength.has an extremely short wavelength. has no mass since it is energy.has no mass since it is energy. travel at the speed of light.travel at the speed of light. can cause air and most materials to can cause air and most materials to

become ionized or charged.become ionized or charged. can only be stopped by using 2 to 4 inches can only be stopped by using 2 to 4 inches

of lead or many feet of concrete.of lead or many feet of concrete. does not change the identity of the does not change the identity of the

radionuclide.radionuclide. The symbol is the Greek letter, gammaThe symbol is the Greek letter, gamma

Decay SeriesDecay Series A A decay seriesdecay series is a series of radioactive is a series of radioactive

nuclides produced by successive nuclides produced by successive radioactive decay until a stable nuclide radioactive decay until a stable nuclide is reached.is reached.

The heaviest nuclide in a decay series is The heaviest nuclide in a decay series is called the called the parent nuclideparent nuclide..

The particles in a decay series that are The particles in a decay series that are produced from parent nuclides are called produced from parent nuclides are called daughter nuclidesdaughter nuclides..

U-238 the parent nuclide decays to Pb-U-238 the parent nuclide decays to Pb-206, which is stable and non-radioactive.206, which is stable and non-radioactive.

U-238 Decay SeriesU-238 Decay Series

Units of Radioactivity:Units of Radioactivity: Roentgen:Roentgen: the amount of gamma or the amount of gamma or

x-rays required to produce one unit x-rays required to produce one unit of electrical charge per cubic of electrical charge per cubic centimeter from ionization of air. (1 centimeter from ionization of air. (1 roentgen = 86 ergs per gram)roentgen = 86 ergs per gram)

REP:REP: (roentgen equivalent units) the (roentgen equivalent units) the amount of radiation to produce an amount of radiation to produce an harmful effect on living tissue.harmful effect on living tissue.

REM:REM: (roentgen equivalent man) the (roentgen equivalent man) the amount of radiation that produces amount of radiation that produces the same biological damage in man the same biological damage in man resulting from the absorption of 1 resulting from the absorption of 1 REP of radiation. REP of radiation.

Additional Units of Additional Units of Radioactivity Radioactivity

Curie:Curie: the number of nuclear the number of nuclear disintegrations that occur in one second. disintegrations that occur in one second. Commonly used in medical laboratory Commonly used in medical laboratory diagnostic procedures. diagnostic procedures. One cure is 3.7 x 10One cure is 3.7 x 101010 nuclear nuclear disintegrations.disintegrations.

RAD:RAD: (radiation absorbed dose) similar to a (radiation absorbed dose) similar to a REM, and is used in monitoring dosimeter REM, and is used in monitoring dosimeter measurements for X-ray personnel.measurements for X-ray personnel.

Sievert(Sv)- SI derived unit of dose and Sievert(Sv)- SI derived unit of dose and reflects the biological effects of radiation reflects the biological effects of radiation that is absorbed (in gray units).that is absorbed (in gray units).

REMS, and RADS are the two most common REMS, and RADS are the two most common units for measuring radiation exposure.units for measuring radiation exposure.

Exposure Limits:Exposure Limits: Average citizen:Average citizen:

No more than 500 millirems per year. No more than 500 millirems per year. X-rays can cause exposures of 100 X-rays can cause exposures of 100 millirem per procedure.millirem per procedure.

Radiation or Nuclear medicine workers:Radiation or Nuclear medicine workers:No more than 5 rems per year.No more than 5 rems per year.

Physiological effects:Physiological effects:Acute Radiation sickness: 100-400 Acute Radiation sickness: 100-400

remsremsLD-50 (lethal dose 50%):LD-50 (lethal dose 50%): 400 rems 400 remsLD-100 Death: LD-100 Death: over 1000 over 1000

remsrems Hyperlink to Radiation poisoning

Protection from Protection from RadiationRadiationThree factors to protect Three factors to protect

radiation workers areradiation workers areS-S-ShieldingShielding; ; the use of lead and orthe use of lead and or

concrete in high concrete in high radiation areas.radiation areas.

T-T-TimeTime; ; limit the amount oflimit the amount of time in high time in high

radiation areas.radiation areas.D-D-DistanceDistance; ; the farther away from the farther away from

a high radiation areaa high radiation areathe lower the exposure.the lower the exposure.

Shielding GraphicShielding Graphic

Nuclear FissionNuclear Fission When a nucleus fissions, it splits into several When a nucleus fissions, it splits into several

smaller fragments or atoms. smaller fragments or atoms. These fragments, or fission products, are about These fragments, or fission products, are about

equal to half the original mass. equal to half the original mass. Two or three neutrons can also be emitted. Two or three neutrons can also be emitted. The sum of the masses of these fragments is The sum of the masses of these fragments is

less than the original mass. This 'missing' mass less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has (about 0.1 percent of the original mass) has been converted into energy according to been converted into energy according to Einstein's equation.Einstein's equation.

Fission can occur when a nucleus of a heavy Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen atom captures a neutron, or it can happen spontaneouslyspontaneously

Fission ReactorsFission Reactors The heat from a fission reactor is used to The heat from a fission reactor is used to

heat water to steam, which turns heat water to steam, which turns turbines to generate electricity.turbines to generate electricity.

Fuels rods made of aluminum hold the Fuels rods made of aluminum hold the Uranium-235 or U-238 which is the most Uranium-235 or U-238 which is the most common nuclide used in fission reactors.common nuclide used in fission reactors.

Control rods made of neutron-absorbing Control rods made of neutron-absorbing steel are used to limit the number of steel are used to limit the number of free neutrons. free neutrons.

Graphite(carbon) is used to slow down Graphite(carbon) is used to slow down fast neutrons produced from fission. fast neutrons produced from fission.

Control rods allow for a limited self-Control rods allow for a limited self-sustaining reaction.sustaining reaction.

Oak Ridge Fission Oak Ridge Fission ReactorReactor

Production of ElectricityProduction of Electricity

Nuclear FusionNuclear Fusion Nuclear energy can also be released by Nuclear energy can also be released by

fusion of two light elements (elements fusion of two light elements (elements with low atomic numbers).with low atomic numbers).

The power that fuels the sun and the The power that fuels the sun and the stars is nuclear fusion. stars is nuclear fusion.

In a hydrogen bomb, two isotopes of In a hydrogen bomb, two isotopes of hydrogen, deuterium and tritium are hydrogen, deuterium and tritium are fused to form a nucleus of helium and a fused to form a nucleus of helium and a neutron. neutron.

Unlike nuclear fission, there is no limit on Unlike nuclear fission, there is no limit on the amount of the fusion that can occur.the amount of the fusion that can occur.

Applications of Nuclear Applications of Nuclear ChemistryChemistry

Radioactive Dating using C-14Radioactive Dating using C-14 Treatment of Cancer (Phosphorous and Treatment of Cancer (Phosphorous and

Cobalt)Cobalt) NMR and CAT scans in RadiologyNMR and CAT scans in Radiology Sterilization of foodsSterilization of foods Radioactive tracers (cardiology)Radioactive tracers (cardiology) Fission reactors for Electrical Power Fission reactors for Electrical Power Medical Laboratory proceduresMedical Laboratory procedures Defensive and Offensive WeaponsDefensive and Offensive Weapons