Upload
barry-walsh
View
231
Download
3
Tags:
Embed Size (px)
Citation preview
Nuclear Chemistry
23.1
Nuclear Reactions vs. Nuclear Reactions vs. Normal Chemical Normal Chemical
ChangesChanges• Nuclear reactions involve the nucleusNuclear reactions involve the nucleus• The nucleus opens, and protons and The nucleus opens, and protons and
neutrons are rearrangedneutrons are rearranged• The opening of the nucleus releases a The opening of the nucleus releases a
tremendous amount of energy that holds tremendous amount of energy that holds the nucleus together – called the nucleus together – called binding binding energyenergy
• ““Normal” Chemical Reactions involve Normal” Chemical Reactions involve electronselectrons, not protons and neutrons, not protons and neutrons
I. Nuclear Chemistry
A. Wilhem Rontgen - discovered x-rays in 1895
B. Antoine Henri Becquerl - discovered radioactivity
1. photographic plates and rocks
C. Marie and Pierre Curie - discovered other radioactive elements
1. Marie first person to win the Nobel peace prizetwice
2. husband run over by wagon when he was crossing the street
3. Marie and her children died of radiation poisoning
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 ofparticles came from the work of
Marie CurieMarie Curie (1876-1934).(1876-1934). • She discoveredShe discovered radioactivityradioactivity, ,
the spontaneous disintegration of the spontaneous disintegration of some elements into smaller pieces.some elements into smaller pieces.
II. Radioactivity
A. Spontaneous break down of an unstable nucleus with the release of particles and rays
B. Mass defect and nuclear stability
1. the sum of the particles(protons, neutrons and electrons) that make up an atom but does not add up to the mass of an atom
2. the difference between the sum of the masses and the atomic mass is know as the mass defect
Mass DefectMass Defect
• Some of the mass can be converted into Some 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
C. Nuclear binding energy
1. The energy released when a nucleus is formedfrom nucleons (protons and neutrons)
III Properties of Radioactive elements
1. They affect photographic film
2. They produce electric charges in the surrounding air
3. They produce fluorescence with certain compounds
a. fluorescence - makes thing glow
4. Their radiation’s have special physiological effects
a. causes mutations in cells - changes in the
DNA of cells causing rapid growth and a
change in their function
5. They undergo radioactive decay
a. Radioactive decay - they emit particles from the nucleus making simpler atoms
i. half-life - the time it takes 1/2 a given
amount to decay
ii. Half-lives can be from a few seconds
to millions of years
Half-LifeHalf-Life
• HALF-LIFEHALF-LIFE is the time that it takes for is the time that it takes for 1/2 a sample to decompose.1/2 a sample to decompose.
• The rate of a nuclear transformation The rate of a nuclear transformation depends only on the “reactant” depends only on the “reactant” concentration.concentration.
Kinetics of Radioactive Kinetics of Radioactive DecayDecay
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
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?
e.g. The half-life of Plutonium -239 is 24110 years. Of an original mass of 100. g, how much remains after 96440 years
first find the number of half-life's
# Half-lifes = 96440 years 24110 Years
= 4
now divide the gram sample in 1/2 four times
100 ===> 6.25===>12.5===> 25===> 50
1 2 3 4
The half-life of thorium -227 is 18.72 days. How many days are required for 3/4 of a given amount to decay
1 ===> 1/2 ===> 1/4
This tells you that you have 1/4 of the original amount left - therefore - 3/4 of a given amount has decayed
you must multiply 18.72 days by 2 == 37.44 days
18.72 days 18.72 days
e.g Exactly 1/16 of a given amount of protactinium-234 remains after 26.76 hours. What is the half-life of
protactinium - 234
First find the number of half-life's
1 ==> 1/2 ===> 1/4 ===> 1/8 ===> 1/16
You must pass threw 4 half life’s
26.76 hours4 half-life’s
= 6.69 hours/half-life
The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 78 hours?
Nuclear Stability
• Certain numbers of neutrons and protons are extra stable
• n or p = 2, 8, 20, 50, 82 and 126
• Like extra stable numbers of electrons in noble gases (e- = 2, 10, 18, 36, 54 and 86)
• Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons
• All isotopes of the elements with atomic numbers higher than 83 are radioactive
• All isotopes of Tc and Pm are radioactive
23.2
Band of Stability and Band of Stability and Radioactive DecayRadioactive Decay
When the number of protons in a stable nuclei is plotted against the number of neutrons
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
Radioactive decay
1. types of particles
a. alpha particles, contain two protons and
two neutrons - can be stopped by a piece of
paper - have low penetrating power - may
cause burns to the flesh
b. beta particles,, high speed electrons, travel at close to the speed of light, c, which is
equal to 3 x 108 m/sec or 186,000 miles a sec
c. gamma rays,, are high energy electromagnetic waves. Most penetrating
Types of RadiationTypes of Radiation
e01
He42
• Alpha – a positively charged Alpha – a positively charged (+2) helium isotope(+2) helium isotope - - we usually we usually ignore the charge because it involves electrons, ignore the charge because it involves electrons, not protons and neutronsnot protons and neutrons
•Beta – an electronBeta – an electron
•Gamma – pure energy; Gamma – pure energy; called a ray rather than a called a ray rather than a particleparticle
00
Other Nuclear ParticlesOther Nuclear Particles
e01
n10• NeutronNeutron
• Positron – a positive Positron – a positive electronelectron
•Proton – usually referred to Proton – usually referred to as hydrogen-1as hydrogen-1
•Any other elemental isotopeAny other elemental isotope
H11
Penetrating AbilityPenetrating Ability
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
23.1
3. radioactive decay sequence
238U92 ----> + 234Th90
parent daughter
when you have an alpha ejection - you lose 2 protons and 2 neutron
The 92 of uranium is the number of protons and will go to 90 with an alpha ejection - the number of protons in you nucleus determines the element.
therefore - U turns into Th
The 238 of U is the total number of particles in
the nucleus = number of protons and neutrons -
with an alpha ejection - you lose 2 protons and 2
neutrons your mass goes down by 4 or become 234
226Ra88 ----> + 222Rn86
When you have a beta ejection - you have a neutron change to a protons thus causing your number of protons to go up by one. The total number of particles in the nucleus does not change
234Pa91 ----> 234U92
+ beta particle
234Th90 ---->234Pa91
+
On page 724 do problems 33,34,35,40,41,42,43
212Po 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
23.1
Nuclear 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 = 023.2
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 49 023.2
What radioactive isotope is produced in the following bombardment of boron?
10B + 4He ? + 1n
5 2 0
What radioactive isotope is produced in the following bombardment of boron?
10B + 4He 13N + 1n
5 2 7 0
Write Nuclear Equations!
Write the nuclear equation for the beta emitter Co-60.
6060CoCo 00ee ++ 6060NiNi2727 -1 -1 2828
Positron emission -conversion of a proton to a neutron bythe emission of a positron
1. Positron - particle that has the same mass as an
electron, but has a positive charge
Gamma radiation - does not change the identity of the element but makes the atom more stable
Transmutation - changing the identity of an element through the release of radioactive particles
Isotopes - atoms of the same element that have different number of neutrons
Geiger-Müller Counter
23.7
Geiger Counter
• Used to detect radioactive substances
Artificial 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
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 reactions. reactions.
Artificial Nuclear Artificial Nuclear ReactionsReactions
Example of a Example of a reaction reaction is production is production
of radioactive of radioactive 3131P for use in studies of P P for use in studies of P
uptake in the body.uptake in the body.
31311515P + P + 11
00n ---> n ---> 32321515P + P +
Transuranium ElementsTransuranium Elements
Elements beyond 92 Elements beyond 92 (transuranium)(transuranium) made made
starting with an starting with an 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
23.8
Biological 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
Effects of RadiationEffects of Radiation
Nuclear FissionNuclear FissionFission is the splitting of atomsFission is the splitting of atoms
These are usually very large, so that they are not as stableThese are usually very large, so that they are not as stable
Fission chain has three general steps:Fission chain has three general steps:
1.1. Initiation.Initiation. Reaction of a single atom starts the Reaction of a single atom starts the
chain (e.g., chain (e.g., 235235U + neutron)U + neutron)
2.2. PropagationPropagation. . 236236U fission releases neutrons that U fission releases neutrons that
initiate other fissionsinitiate other fissions
3. 3. TerminationTermination. .
Nuclear FissionNuclear Fission
Nuclear Fission
23.5
235U + 1n 90Sr + 143Xe + 31n + Energy92 54380 0
Energy = 3.3 x 10-11J per 235U
= 2.0 x 1013 J per mole 235U
Combustion of 1 ton of coal = 5 x 107 J
= 235 grams = 0.5 lbs
Representation of a fission process.
Nuclear Fission
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
Nuclear 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.
Diagram of a nuclear power plant
Annual Waste Production
23.5
35,000 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
Nuclear Fusion
Fusion small nuclei combine
2H + 3H 4He + 1n +
1 1 2 0
Occurs in the sun and other stars
Energy
Nuclear Fusion
Fusion
• Excessive heat can not be contained
• Attempts at “cold” fusion have FAILED.
• “Hot” fusion is difficult to contain
23.7
Radioisotopes 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
protection from radiation
A. Shielding
sunscreen, lead apron
B. distance
- inverse square law
Nagasaki JapanAugust 9, 1945
Nuclear review
1. A radioactive atom will lose the greatest amount of mass when it emits 1. a neutron' 3.a beta particle , 2. a proton 4.an alpha particle
2 A sample of iodine-131 contains 10. grams. Approximately how much iodine-131 will remain after 24 days
(half life -8 days)? 1. 1.25g 3. 5.0 g
2. 2.5 g 4. 10. g
3. What is the moderator in a nuclear reactor? 1. carbon dioxide 3. cadmium 2. boron 4. graphite
You have a review test
4. In the reaction 90Th234 -> 91Pa234 + X, X represents
1.a neutron 3. an alpha particle 2.a positron 4. a beta particle
5. One of the biggest advantages of a fusion reactor is it 1. produces no radioactive wastes 2. is small in size 3. will never explode 4. has no reaction control problem
6. Which particle has the least mass? 1. alpha particle 2. proton 3. neutron 4. electron
7. A neutron has approximately the same mass as 1. an alpha particle 3. an electron 2. a beta particle 4. a proton
8. When 88Ra226 emits an alpha particle, the resulting atom is
1. 86 Rn 2 2 2
2. 86 Rn 2 2 4
3. 88 Ra 2 2 2
4. 88 Ra 2 2 4
9. To make nuclear fission nuclear reactor more efficient, which device is used to slow the speed of neutrons?
1. internal shield 2. external shield 3.control rod 4.moderator
10. If radioactive substance has a half-life of 9 days, what fraction of its original mass would remain after 27 days? 1. 1/8 2. 1/4 3. 1/2 4. 3/4
11. Which reaction illustrates fusion? 1. 1 H
2 + 1 H2 ===> 2He4
2. on1 + 13A127 ==> 11Na24 + 2He4
3. 13A127 + 2He4 ===> 15P30 + 2 He4 + 0 n
1
4. 7 N1 4 + 2 He4 ===> 1 H
1 + 8O17
12.Control rods in nuclear reactors are commonly made of boron and cadmium because these two elements have the ability to 1) absorb neutrons 2) emit neutrons 3) decrease the speed of neutrons 4) increase the speed of neutrons
13. If iodine-131 undergoes beta decay, which symbol represents the resulting nucleus?
1. 52Te132 2. 54Xe131 3. 53I130 4. 51 Sb1 27
14. Which element is formed when 82Pb214 emits a beta particle?
1. 84 Po 21 8 2. 80 Hg 2 0 0 3. 83Bi213 4. 83Bi214
15.Radioactive changes differ from ordinary chemical changes In that radioactive changes 1.are explosive 3.involve changes in the nucleus 2.absorb energy 4.release energy
16. In the reaction
4Be9 + X ----> 6 C12 + 0 n1 the X represents
1.an alpha particle 3.an electron 2.a beta particle 4.a proton
18. Which nuclear equation represents beta decay? 1. 13A127 + 2He4 --> 15P
30 + on1
2 . 92 U2 3 8 -- -> 90 Th2 3 4 + 2 He4
3. 6 C1 4 - -> 7 N
1 4 + - 1 e0
4. 18Ar37 + -1 eo --> 17Cl37
19. An atom of Ra226 decays to Rn222 by emitting 1.a proton 3. an alpha particle 2.an electron 4. a beta particle
20. Heavy water may be used in a nuclear reactor as a 1.moderator 3. shielding 2.fuel 4. control rod
21.When an atom emits a beta particle, the total number of nucleons 1. decreases 2. increases 3. remains the same
22. The radioactive particle or ray with the greatest penetrating power is the
1.alpha particle 3.gamma ray 2.beta particle 4.proton
23. The major portion of an atom's mass consists of 1) electrons and protons 3) neutrons and positrons 2) electrons and neutrons 4) neutrons and protons
24. During a chain reaction the number of nuclei reacting per second 1. increases 2. decreases 3. remains the same
25. A radioactive source emits radiation which is deflected as shown in the diagram. .
This radiation could be
1. _1eo
2. 2 He4
3. 1 H1
4. 0 n1
26.When 90Th234 emits a beta particle ( -1 e0), the element
formed is 1. Ra 2. Th 3. Pa 4. U
27. A 40.0 milligram sample of phosphorus -33 decays to 10.0 milligrams in 50.0 days. What is the half-life of
phosphorus-33? 1.12.5 days 3.37.5 days 2.25.0 days 4.75.0 days
28. During a fission reaction, which type of particle is captured by a nucleus? 1.deuterium 3.neutron 2.electron 4.proton
29.When two light nuclei combine into a heavier nucleus, the process is called
1.fission 3.beta decay 2.fusion 4.nuclear disintegration
30, An electron has a charge identical to that of 1. a neutron 3. an alpha particle 2.a proton 4. a beta particle
31. In the reaction 92U238 --> 90Th234 + X, X represents
1.a beta particle 3. a positron 2.a neutron 4. an alpha particle
23.6
Nuclear Fusion
2H + 2H 3H + 1H1 1 1 1
Fusion Reaction 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
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.
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 + 2x023.1
Radiocarbon 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
23.3