ap ch 23 nuclear

8/8/2019 AP Ch 23 Nuclear

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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


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


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.

ap ch 23 nuclear

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