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Nuclear Chemistry
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RadioactivityRadioactivity
One of the pieces of evidence for theOne of the pieces of evidence for the
fact that atoms are made of smallerfact that atoms are made of smaller
particles came from the work ofparticles came from the work of
Marie CurieMarie Curie (1876(1876--1934).1934). She discoveredShe discovered radioactivityradioactivity,,
the spontaneous disintegration ofthe spontaneous disintegration of
some elements into smaller pieces.some elements into smaller pieces.
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Nuclear Reactions vs.Nuclear Reactions vs.Normal Chemical Changes
Normal Chemical Changes
Nuclear reactions involve the nucleusNuclear reactions involve the nucleus The nucleus opens, and protons andThe nucleus opens, and protons and
neutrons are rearrangedneutrons are rearranged The opening of the nucleus releases aThe opening of the nucleus releases a
tremendous amount of energy that holdstremendous amount of energy that holdsthe nucleus togetherthe nucleus together calledcalled bindingbinding
energyenergy Normal Chemical Reactions involveNormal Chemical Reactions involveelectronselectrons, not protons and neutrons, not protons and neutrons
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23.1
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Types of Radiation
Types of Radiation
e0
1
He4
2
Alpha (Alpha ()) a positivelya positively
charged (+2) helium isotopecharged (+2) helium isotope --we usually ignore the charge because it involveswe usually ignore the charge because it involveselectrons, not protons and neutronselectrons, not protons and neutrons
Beta (Beta ()) an electronan electron
Gamma (Gamma ()) pure energy;pure energy;
called a ray rather than acalled a ray rather than a
particleparticleK0
0
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Other
Nuclear Particles
Other
Nuclear Particles
e0
1
n1
0 NeutronNeutron
PositronPositron a positivea positiveelectronelectron
ProtonProton usually referred tousually referred to
as hydrogenas hydrogen--11
Any other elemental isotopeAny other elemental isotope
H
1
1
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Penetrating AbilityPenetrating Ability
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Geiger-Mller Counter
23.7
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Geiger Counter
Used to detect radioactive substances
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XAZMass 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
1p1
1H1or
proton1n0
neutron0e-1
0F-1or
electron0e+1
0F+1or
positron4He2
4E2or
E particle
1
1
1
0
0
-1
0
+1
4
2
23.1
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Balancing 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.
1
n0U235
92 + Cs138
55 Rb9637
1
n0+ + 2
235 + 1 = 138 + 96 + 2x1
2. Conserve atomic number (Z) or nuclear charge.
The sum of nuclear charges in the products must equal thesum of nuclear charges in the reactants.
1n0U235
92 + Cs138
55 Rb9637
1n0+ + 2
92 + 0 = 55 + 37 + 2x0 23.1
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212Po decays by alpha emission. Write the balanced
nuclear equation for the decay of212Po.
4He2
4E2oralpha particle -
212Po 4He + AX84 2 Z
212 = 4 +A A = 208
84 = 2 + Z Z = 82
212Po 4He + 208Pb84 2 82
23.1
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Nuclear Stability and Radioactive Decay
Beta decay
14C 14N + 0F + R6 7 -1
40K 40Ca + 0F + R19 20 -1
1
n1
p + 0F + R0 1 -1
Decrease # of neutrons by 1
Increase # of protons by 1
Positron decay
11C 11B + 0F + R6 5 +1
38K 38Ar + 0F + R19 18 +1
1p 1n + 0F + R1 0 +1
Increase # of neutrons by 1
Decrease # of protons by 1
R and R haveA = 0 and Z = 0 23.2
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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 + R18 17-1
55Fe + 0e 55Mn + R26 25-1
1
p +0
e1
n + R1 0-1
Alpha decay
Decrease # of neutrons by 2
Decrease # of protons by 2
212Po 4He + 208Pb84 2 82
Spontaneous fission
252Cf 2125In + 21n98 49 0
23.2
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Learning Check
What radioactive isotope is produced in the
following bombardment of boron?
10B + 4He 13N + 1n
5 2 7 0
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Write
Nuclear Equations!
Write the nuclear equation for the beta
emitter Co-60.
6060CoCo 00ee ++ 6060NiNi
2727 --11 2828
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Artificial Nuclear ReactionsArtificial Nuclear Reactions
New elements or new isotopes of known elementsNew elements or new isotopes of known elements
are produced by bombarding an atom with aare produced by bombarding an atom with a
subatomic particle such as a proton or neutronsubatomic particle such as a proton or neutron
---- or even a much heavier particle such asor even a much heavier particle such as 44HeHeandand 1111B.B.
Reactions using neutrons are calledReactions using neutrons are called
KK reactionsreactions because abecause a KK ray is usuallyray is usuallyemitted.emitted.Radioisotopes used in medicine are often made byRadioisotopes used in medicine are often made by
KK reactions.reactions.
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Artificial Nuclear ReactionsArtificial Nuclear Reactions
Example of aExample of a KK reactionreaction is productionis production
of radioactiveof radioactive3131
P for use in studies of PP for use in studies of P
uptake in the body.uptake in the body.
31311515P +P +
1100nn ------>>
32321515P +P + KK
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Transuranium ElementsTransuranium Elements
Elements beyond 92Elements beyond 92 (transuranium)(transuranium) mademade
starting with anstarting with an KK reactionreaction
2382389292U +U +
1100nn ------>>
2392399292U +U + KK
239239
9292UU ------>>239239
9393Np +Np +00
--11FF239239
9393NpNp ------>>239239
9494Pu +Pu +00
--11FF
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H
alfH
alf--L
ifeL
ife HALFHALF--LIFELIFE is the time that it takes foris the time that it takes for
1/2 a sample to decompose.1/2 a sample to decompose. The rate of a nuclear transformationThe rate of a nuclear transformation
depends only on the reactantdepends only on the reactant
concentration.concentration.
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HalfHalf--LifeLife
Decay of 20.0 mg ofDecay of 20.0 mg of1515O. What remains after 3 halfO. What remains after 3 half--lives?lives?
After 5 halfAfter 5 half--lives?lives?
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Kinetics of Radioactive DecayKinetics of Radioactive Decay
For each duration (half-life), one half of the
substance decomposes.
For example: Ra-234 has a half-life of 3.6 days
If 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
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Radiocarbon Dating
14N + 1n 14C + 1H7 160
14C 14N + 0F + R6 7 -1 t = 5730 years
Uranium-238 Dating
238U 206Pb + 84E + 60F92 -182 2 t = 4.51x10
9 years
23.3
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Learning Check!
The half life of I-123 is 13 hr. How much of
a 64 mg sample of I-123 is left after 31
hours?
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23.8
Biological Effects ofRadiation
Radiation absorbed dose (rad)
1rad =
1x1
0-5 J/
g of materialRoentgen equivalent forman (rem)
1 rem = 1 rad x Q Quality Factor
K-ray = 1
F = 1E = 20
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Effects of RadiationEffects of Radiation
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Nuclear FissionNuclear Fission
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Representation of a fission process.
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Mass DefectMass Defect
Some of the mass can be converted intoSome of the mass can be converted into
energyenergy
Shown by a very famous equation!Shown by a very famous equation!
E=mcE=mc22
EnergyEnergy
MassMass
Speed of lightSpeed of light
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Nuclear binding energy (BE) is the energy required to break
up a nucleus into its component protons and neutrons.
BE +19
F 91
p + 101
n9 1 0
BE = 9x (p mass) + 10 x (n mass) 19F mass
E = mc2
BE (amu) = 9x1.007825 + 10 x1.008665 18.9984
BE = 0.1587 amu 1 amu = 1.49x10-10 J
BE = 2.37x10-11J
binding energy per nucleon =binding energy
number of nucleons
=2.37x10-11J
19 nucleons= 1.25x10-12 J
23.2
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NuclearFission
23.5
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
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Diagram of a nuclear power plant
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23.6
NuclearFusion
2H + 2H 3H + 1H1 1 1 1
Fusion Reaction Energy Released
2H + 3H 4He + 1n1 1 2 0
6Li +
2H
24H
e3 1 2
6.3x10-13 J
2.8x10-12 J
3.6x10-12 J
Tokamak magnetic
plasma
confinement
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Nuclear
Fusion
Fusion
Excessive heat can not be contained Attempts at cold fusion have
FAILED.
Hot fusion is difficult to contain
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23.7
Radioisotopes in Medicine
1 out of every 3 hospital patients will undergo a nuclear
medicine procedure
24Na, t = 14.8 hr, F emitter, blood-flow tracer
131I, t = 14.8 hr, F emitter, thyroid gland activity
123I, t = 13.3 hr, Kray emitter, brain imaging
18F, t = 1.8 hr, F emitter, positron emission tomography
99mTc, t = 6 hr, Kray emitter, imaging agent
Brain images
with 123I-labeled
compound
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Chemistry In Action: Food Irradiation
Dosage Effect
Up to 100 kilorad
Inhibits sprouting of potatoes, onions, garlics.
Inactivates trichinae in pork. Kills or prevents insects
from reproducing in grains, fruits, and vegetables.
100 1000 kiloradsDelays 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.