chapter23_Nuclear.ppt

1Chemistry and Chemical Reactivity 6th Edition

John C. Kotz Paul M. Treichel

Gabriela C. Weaver

CHAPTER 23

Nuclear Chemistry

Lecture written by John Kotz as modified by George Rhodes

2

Chapter Goals p-1139• Identify radioactive elements and describe natural and

artificial nuclear reactions• Calculate the binding energy and binding energy per

nucleon for a particular isotope• Understand rates of radioactive decay• Understand artificial nuclear reactions• Understand issues of health and safety with respect to

radioactivity• Become aware of their use in science and medicine

3

Nuclear ChemistryNuclear Chemistry

Pictures of human Pictures of human heart before and after heart before and after

stress using gamma stress using gamma rays from radioactive rays from radioactive

Tc-99m Tc-99m

4

Enrico Fermi

• Nuclear physicist who worked on the Manhattan Style Clam Chowder Project. When asked later to explain why he was involved in such an endeavor, he replied, "I'm lactose intolerant."

5

Or, Fermi

• was an Italian physicist most noted for his work on beta decay, the development of the first nuclear reactor, and for the development of quantum theory. Fermi won the 1938 Nobel Prize for his work on induced radioactivity.

6

ATOMIC COMPOSITIONATOMIC COMPOSITION• ProtonsProtons

– + electrical charge+ electrical charge– mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g g– relative mass = 1.007 atomic mass units (amu)relative mass = 1.007 atomic mass units (amu)

• ElectronsElectrons– negative electrical chargenegative electrical charge– relative mass = 0.0005 amurelative mass = 0.0005 amu

• NeutronsNeutrons– no electrical chargeno electrical charge– mass = 1.009 amumass = 1.009 amu

• amu = as compared to 1 atom of carbon 12amu = as compared to 1 atom of carbon 12

7

IsotopesIsotopes

• Atoms of the same element (same Z) but Atoms of the same element (same Z) but different mass number (A).different mass number (A).

• Boron-10 (Boron-10 (1010B) has 5 p and 5 n: B) has 5 p and 5 n: 101055BB

• Boron-11 (Boron-11 (1111B) has 5 p and 6 n: B) has 5 p and 6 n: 111155BB

10B

11B

8

RadioactivityRadioactivity

• One of the pieces of evidence for the One of the pieces of evidence for the fact that atoms are made of smaller fact that atoms are made of smaller particles came from the work of particles came from the work of

Marie CurieMarie Curie (1876-1934). (1876-1934). • She discovered She discovered

radioactivityradioactivity, the , the spontaneous disintegration of some spontaneous disintegration of some elements into smaller pieces.elements into smaller pieces.

• Nobel/Physics 1903 for radiation Nobel/Physics 1903 for radiation phenomena and phenomena and

• Nobel/Chemistry 1911 for the Nobel/Chemistry 1911 for the discoveries of Ra and Podiscoveries of Ra and Po

9

Types of Ionizing Types of Ionizing RadiationRadiation

10

XAZ

Mass Number

Atomic NumberElement Symbol

Atomic number (Z) = number of protons in nucleus

Mass number (A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

A

Z

1p11H1or

proton1n0

neutron0e-1

0-1or

electron0e+1

0+1or

positron4He2

42or

particle

1

1

1

0

0

-1

0

+1

4

2

11

Penetrating AbilityPenetrating Ability

12

Nuclear ReactionsNuclear Reactions

• Ernest Rutherford* found Ra forms Rn gas

when emitting an alpha particle.

• 1902—Rutherford and Soddy proposed

radioactivity is the result of the natural change

of the isotope of one element into an isotope of

a different element.

• *Nobel/Chemistry 1908

13


• Alpha emissionAlpha emission

Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.

Nucleons are rearranged but conserved

14


• Beta emissionBeta emission

Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.

How does this happen?

So, the e- (β particle) is emitted while the proton remains with the nucleus

15Balancing Nuclear Equations

1. Conserve mass number (A).

The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

235 + 1 = 138 + 96 + 2x1

2. Conserve atomic number (Z) or nuclear charge.

The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

92 + 0 = 55 + 37 + 2x0

16212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.

4He242oralpha particle -

212Po 4He + AX84 2 Z

212 = 4 + A A = 208

84 = 2 + Z Z = 82

212Po 4He + 208Pb84 2 82

17Nuclear Stability and Radioactive Decay

Beta decay

14C 14N + 0 + 6 7 -1

40K 40Ca + 0 + 19 20 -1

1n 1p + 0 + 0 1 -1

Decrease # of neutrons by 1

Increase # of protons by 1

Positron decay

11C 11B + 0 + 6 5 +1

38K 38Ar + 0 + 19 18 +1

1p 1n + 0 + 1 0 +1

Increase # of neutrons by 1

Decrease # of protons by 1

and have A = 0 and Z = 0

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Electron capture decay

Increase # of neutrons by 1

Decrease # of protons by 1

Nuclear Stability and Radioactive Decay

37Ar + 0e 37Cl + 18 17-1

55Fe + 0e 55Mn + 26 25-1

1p + 0e 1n + 1 0-1

Alpha decay

Decrease # of neutrons by 2

Decrease # of protons by 2212Po 4He + 208Pb84 2 82

Spontaneous fission

252Cf 2125In + 21n98 49 0

19

Gamma rays

• Gamma rays are often produced alongside other forms of radiation such as alpha or beta. When a nucleus emits an α or β particle, the daughter nucleus is sometimes left in an excited state. It can then jump down to a lower level by emitting a gamma ray in much the same way that an atomic electron can jump to a lower level by emitting visible light or ultraviolet radiation.

20Radioactive Decay SeriesRadioactive Decay Series

21Other Types of Nuclear Other Types of Nuclear ReactionsReactions

Positron (Positron (00+1+1): a positive electron): a positive electron

K-capture:K-capture: the capture of an electron from the first or K shell

An electron and proton combine to form a neutron.0

-1e + 11p --> 1

0n

207 207

22

Origin of the ElementsOrigin of the Elements

• The Big Bang Theory The Big Bang Theory • In the first moments there were only In the first moments there were only 2 elements — hydrogen and helium2 elements — hydrogen and helium

23Stability Stability of of NucleiNuclei

24

Stability of NucleiStability of Nuclei

• H is most abundant element in the universe.H is most abundant element in the universe.– 88.6% of all atoms88.6% of all atoms– He is 11.3% of all atomsHe is 11.3% of all atoms– H + He = 99.9% of all atoms & 99% of mass of H + He = 99.9% of all atoms & 99% of mass of

the universe.the universe.

• This tells us about the origin of the This tells us about the origin of the elements, and so does the existence of elements, and so does the existence of isotopes.isotopes.

25Elemental Abundance on Elemental Abundance on EarthEarth

26

IsotopesIsotopes

• Hydrogen: Hydrogen: – 11

11H, protiumH, protium

– 2211H, deuteriumH, deuterium

– 3311H, tritium (radioactive)H, tritium (radioactive)

• Helium, Helium, 4422HeHe

• Lithium, Lithium, 6633Li and Li and

7733LiLi

• Boron, Boron, 101055B and B and 1111

55BB

• IronIron

– 54542626Fe, 5.82% abundantFe, 5.82% abundant




27

IsotopesIsotopes

• Hydrogen: Hydrogen: – 11

11H, protiumH, protium

– 2211H, deuteriumH, deuterium

– 3311H, tritium (radioactive)H, tritium (radioactive)

• Helium, Helium, 4422HeHe

• Lithium, Lithium, 6633Li and Li and 77

33LiLi

• Boron, Boron, 101055B and B and 1111

55BB

• Except for Except for 1111H the mass H the mass

number is always at least number is always at least

2 x atomic number. 2 x atomic number.

• Repulsive forces between Repulsive forces between

protons must be protons must be

moderated by neutrons.moderated by neutrons.

28Stability Stability of of NucleiNuclei

• Heaviest naturally Heaviest naturally

occurring non-occurring non-

radioactive isotope is radioactive isotope is

209209Bi with 83 protons and Bi with 83 protons and

126 neutrons126 neutrons

• There are 83 x 126 = There are 83 x 126 =

10,458 possible isotopes. 10,458 possible isotopes.

Why so few actually Why so few actually

exist?exist?

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Stability of NucleiStability of Nuclei

• Up to Z = 20 (Ca), n = p (except for Up to Z = 20 (Ca), n = p (except for 7733Li, Li, 1111

55B, B, 191999F)F)

• Beyond Ca, n > p (A > 2 Z)Beyond Ca, n > p (A > 2 Z)

• Above Bi all isotopes are radioactive. Fission leads to Above Bi all isotopes are radioactive. Fission leads to

smaller particles, the heavier the nucleus the greater the smaller particles, the heavier the nucleus the greater the

rate.rate.

• Above Ca: elements of EVEN Z have more isotopes and Above Ca: elements of EVEN Z have more isotopes and

most stable isotope has EVEN N.most stable isotope has EVEN N.

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Stability Stability of of NucleiNuclei

• Out of > 300 stable isotopes:

EvenEven OddOdd

OddOdd

EvenEven

ZZNN

157157 5252

5050 55

31311515PP

191999FF

2211H, H, 66

33Li, Li, 101055B, B, 1414

77N, N, 1801807373TaTa

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Stability of Stability of NucleiNuclei

• Suggests some PAIRING of NUCLEONS• There are “nuclear magic numbers”

2 He 28 Ni8 O 50 Sn20 Ca 82 Pb

EvenEven OddOdd

OddOdd

EvenEven

ZZ NN

157157 5252

5050 55

32Band of Stability Band of Stability and Radioactive and Radioactive DecayDecay 243

95Am --> 42 + 239

93Np

emission reduces Z

emission increases Z

6027Co --> 0

-1 + 6028Ni

Isotopes with low n/p ratio, below band of stability decay, decay by positron emission or electron capture

33

Binding Energy, EBinding Energy, Ebb

EEbb is the energy required to separate the is the energy required to separate the

nucleus of an atom into protons and nucleus of an atom into protons and

neutrons.neutrons.

For deuterium, For deuterium, 2211HH

2211H ---> H ---> 11

11p + p + 1100nn EEbb = 2.15 x 10 = 2.15 x 1088 kJ/mol kJ/mol

EEbb per nucleon per nucleon = E = Ebb/2 nucleons/2 nucleons

= 1.08 x 10= 1.08 x 1088 kJ/mol nucleons kJ/mol nucleons

34Calculate Binding Calculate Binding EnergyEnergy

For deuterium, For deuterium, 2211H: H: 22

11H ---> H ---> 1111p + p + 11

00nn

Mass of Mass of 2211H = 2.01410 g/molH = 2.01410 g/mol

Mass of proton = 1.007825 g/molMass of proton = 1.007825 g/mol

Mass of neutron = 1.008665 g/mol =2.01649Mass of neutron = 1.008665 g/mol =2.01649

∆∆m = 0.00239 g/molm = 0.00239 g/mol

From Einstein’s equation: From Einstein’s equation:

EEbb = (∆m)c = (∆m)c22 = 2.15 x 10 = 2.15 x 1088 kJ/mol kJ/mol

EEbb per nucleon = E per nucleon = Ebb/2 nucleons /2 nucleons

= 1.08 x 10= 1.08 x 1088 kJ/mol nucleons kJ/mol nucleons

35Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons.

BE + 19F 91p + 101n9 1 0

BE = 9 x (p mass) + 10 x (n mass) – 19F mass

E = mc2

BE (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984

BE = 0.1587 amu 1 amu = 1.49 x 10-10 J

BE = 2.37 x 10-11J

binding energy per nucleon = binding energy

number of nucleons

= 2.37 x 10-11 J19 nucleons

= 1.25 x 10-12 J

36

E = mc2

• To use this equation:

• 1. convert mass defect to kg

• 2. c= m/s or 3x108 then

• 3. 3x108 squared = 9x 1016 and this times the mass defect = J

37

Binding EnergyBinding Energy

38Binding Binding Energy/NucleonEnergy/Nucleon

39

Half-LifeHalf-LifeSection 15.4 Section 15.4

• HALF-LIFEHALF-LIFE is the time it takes for 1/2 a is the time it takes for 1/2 a sample to disappear.sample to disappear.

• The rate of a nuclear transformation depends The rate of a nuclear transformation depends only on the “reactant” concentration.only on the “reactant” concentration.

• Concept of HALF-LIFE is especially useful for Concept of HALF-LIFE is especially useful for 1st order reactions.1st order reactions.

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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?

41Kinetics of Radioactive Kinetics of Radioactive DecayDecay

Activity (A) = Disintegrations/time = (k)(N)

where N is the number of atoms

Decay is first order, and so

ln (A/Ao) = -kt

The half-life of

radioactive decay is

t1/2 = 0.693/k

42

Radiocarbon DatingRadiocarbon DatingRadioactive C-14 is formed in the upper atmosphere Radioactive C-14 is formed in the upper atmosphere

by nuclear reactions initiated by neutrons in cosmic by nuclear reactions initiated by neutrons in cosmic radiationradiation

1414N + N + 11oon ---> n ---> 1414C + C + 11HH

The C-14 is oxidized to COThe C-14 is oxidized to CO22, which circulates through , which circulates through

the biosphere.the biosphere.

When a plant dies, the C-14 is not replenished.When a plant dies, the C-14 is not replenished.

But the C-14 continues to decay with tBut the C-14 continues to decay with t1/21/2 = 5730 years. = 5730 years.

Activity of a sample can be used to date the sample.Activity of a sample can be used to date the sample.

43Radiocarbon Dating

14N + 1n 14C + 1H7 160

14C 14N + 0 + 6 7 -1 t½ = 5730 years

Uranium-238 Dating

238U 206Pb + 8 4 + 6 092 -182 2 t½ = 4.51 x 109 years

44

Radiocarbon DatingRadiocarbon Dating

45Artificial Nuclear Artificial Nuclear ReactionsReactions

New elements or new isotopes of known elements New elements or new isotopes of known elements are produced by bombarding an atom with a are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- subatomic particle such as a proton or neutron -- or even a much heavier particle such as or even a much heavier particle such as 44He and He and 1111B.B.

Reactions using neutrons are called Reactions using neutrons are called

n,n, reactions reactions because a because a ray is usually ray is usually emitted.emitted.

Radioisotopes used in medicine are often made by Radioisotopes used in medicine are often made by n,n, reactions. reactions.

46Artificial Nuclear Artificial Nuclear ReactionsReactions

Example of a Example of a n,n, reaction reaction is is

production of radioactive production of radioactive 3131P for use in P for use in

studies of P uptake in the body.studies of P uptake in the body.

31311515P + P + 11

00n ---> n ---> 32321515P + P +

47

Transuranium ElementsTransuranium Elements

Elements beyond 92 Elements beyond 92 (transuranium)(transuranium) made made

starting with an starting with an n,n, reaction reaction

2382389292U + U + 11

00n ---> n ---> 2392399292U + U +

2392399292U U ---> ---> 239239

9393Np + Np + 00-1-1

2392399393Np Np ---> ---> 239239

9494Pu + Pu + 00-1-1

48

Annual Waste Production35,000 tons SO2

4.5 x 106 tons CO2

1,000 MW coal-firedpower plant

3.5 x 106

ft3 ash

1,000 MW nuclearpower plant

70 ft3 vitrified waste

Nuclear Fission

49

TransuraniTransuranium um

Elements & Elements & Glenn Glenn

SeaborgSeaborg

106106SgSg

50

Nuclear FissionNuclear Fission

51Nuclear Fission

Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions.The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass.

Non-critical

Critical

52

Nuclear FissionNuclear Fission

Fission chain has three general steps:Fission chain has three general steps:

1.1. Initiation.Initiation. Reaction of a single atom Reaction of a single atom

starts the chain (e.g., starts the chain (e.g., 235235U + neutron)U + neutron)

2.2. PropagationPropagation. . 236236U fission releases U fission releases

neutrons that initiate other fissionsneutrons that initiate other fissions

3. 3. TerminationTermination. .

53Nuclear Fission

Schematic diagram of a

nuclear fission reactor

54

Nuclear Nuclear Fission & Fission &

Lise Lise MeitnerMeitner

109109MtMt

55Nuclear Fission & Nuclear Fission & POWERPOWER

• Currently about 103 Currently about 103

nuclear power plants in nuclear power plants in

the U.S. and about 435 the U.S. and about 435

worldwide.worldwide.

• 17% of the world’s 17% of the world’s

energy comes from energy comes from

nuclear.nuclear.

56Units for Measuring Units for Measuring RadiationRadiation

Curie: 1 Ci = 3.7 x 10Curie: 1 Ci = 3.7 x 101010 distintegrations/s distintegrations/s

SI unit is the becquerel: 1 Bq = 1 dpsSI unit is the becquerel: 1 Bq = 1 dps

Rad: measures amount of energy absorbedRad: measures amount of energy absorbed

1 rad = 0.01 J absorbed/kg tissue1 rad = 0.01 J absorbed/kg tissue

Rem: based on rad and type of radiation. Rem: based on rad and type of radiation.

Quantifies biological tissue damageQuantifies biological tissue damage

Usually use “millirem”Usually use “millirem”

57

Effects of RadiationEffects of Radiation

58

59Nuclear Medicine: Nuclear Medicine: ImagingImaging


Technetium-99m is used in more than 85% Technetium-99m is used in more than 85%

of the diagnostic scans done in hospitals of the diagnostic scans done in hospitals

each year. Synthesized on-site from Mo-99.each year. Synthesized on-site from Mo-99.

99994242Mo ---> Mo ---> 99m99m

4343Tc + Tc + 00-1-1

99m99m4343Tc decays to Tc decays to 9999

4343Tc giving off Tc giving off ray. ray.

Tc-99m contributes in sites of high activity.Tc-99m contributes in sites of high activity.


Imaging of a Imaging of a heart using heart using Tc-99m before Tc-99m before and after and after exercise.exercise.

62

BNCTBNCTBoron Neutron Capture Boron Neutron Capture

TherapyTherapy• 1010B isotope (not B isotope (not 1111B) has the ability to B) has the ability to

capture slow neutronscapture slow neutrons

• In BNCT, tumor cells preferentially take In BNCT, tumor cells preferentially take

up a boron compound, and subsequent up a boron compound, and subsequent

irradiation by slow neutrons kills the irradiation by slow neutrons kills the

cells via the energetic cells via the energetic 1010B --> B --> 77Li neutron Li neutron

capture reaction (that produces a capture reaction (that produces a

photon and an alpha particle)photon and an alpha particle)

• 1010B + B + 11n ---> n ---> 77Li + Li + 44He + photonHe + photon

63

Food Food IrradiationIrradiation

•Food can be irradiated with Food can be irradiated with rays from rays from 6060Co or Co or 137137Cs.Cs.•Irradiated milk has a shelf life of 3 mo. Irradiated milk has a shelf life of 3 mo.

without refrigeration.without refrigeration.•USDA has approved irradiation of meats USDA has approved irradiation of meats

and eggs.and eggs.

64

Accelerator Transmutation of Waste

65Chemistry In Action: Nature’s Own Fission Reactor

Natural Uranium

0.7202 % U-235 99.2798% U-238

Measured at Oklo

0.7171 % U-235

66Nuclear Fusion

2H + 2H 3H + 1H1 1 1 1

Fusion Reactions Energy Released

2H + 3H 4He + 1n1 1 2 0

6Li + 2H 2 4He3 1 2

6.3 x 10-13 J

2.8 x 10-12 J

3.6 x 10-12 J

Tokamak magnetic plasma

confinement

67

Particle Beam Fusion

If a high energy beam of electrons or other particles can be directed onto a tiny pellet or microballoon of deuterium-tritium mixture, it could cause it to explode like a miniature hydrogen bomb, fusing the deuterium and tritium nuclei in a time frame too short for them to move apart.

68

Laser Fusion

• Nova Laser System• Nova is the name given to the second generation laser fusion device at

Lawrence Livermore Laboratories. It employs lasers ten times more powerful than the Shiva laser fusion device and will attempt to reach the breakeven point for fusion. Nova makes use of ten lasers which are focused on a 1 mm diameter target area, dumping 100,000 joules of energy into the target in a nanosecond.

• As of 1994, Nova approached the Lawson criterion, but at a temperature too low for fusion ignition.

• Once a critical ignition temperature for nuclear fusion has been achieved, it must be maintained at that temperature for a long enough confinement time at a high enough ion density to obtain a net yield of energy.

69Radioisotopes in Medicine• 1 out of every 3 hospital patients will undergo a nuclear

medicine procedure

• 24Na, t½ = 14.8 hr, emitter, blood-flow tracer

• 131I, t½ = 14.8 hr, emitter, thyroid gland activity

• 123I, t½ = 13.3 hr, ray emitter, brain imaging

• 18F, t½ = 1.8 hr, emitter, positron emission tomography

• 99mTc, t½ = 6 hr, ray emitter, imaging agent

Brain images with 123I-labeled compound

70Geiger-Müller Counter

71Biological Effects of RadiationRadiation absorbed dose (rad)

1 rad = 1 x 10-5 J/g of material

Roentgen equivalent for man (rem)

1 rem = 1 rad x Q Quality Factor-ray = 1

= 1 = 20

72Chemistry In Action: Food Irradiation

Dosage Effect

Up to 100 kiloradInhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables.

100 – 1000 kilorads Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit.

1000 to 10,000 kiloradsSterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning.

Technology

chapter23_Nuclear.ppt