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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
Nuclear ReactionsNuclear Reactions
• 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
Nuclear ReactionsNuclear Reactions
• 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
18
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
– 56562626Fe, 91.66% abundantFe, 91.66% abundant
– 57572626Fe, 2.19% abundantFe, 2.19% abundant
– 58582626Fe, 0.33% abundantFe, 0.33% 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?
29
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.
30
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
31
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.
40
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
60Nuclear 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.
61Nuclear Medicine: Nuclear Medicine: ImagingImaging
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.