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Transcript of 1 © 2006 Brooks/Cole - Thomson Review Session: –Tuesday C-106 6-8pm.
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© 2006 Brooks/Cole - Thomson
• Review Session:– Tuesday C-106 6-8pm
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© 2006 Brooks/Cole - Thomson
Chemistry and Chemical Reactivity 6th Edition
John C. Kotz Paul M. Treichel
Gabriela C. Weaver
CHAPTER 23
Nuclear Chemistry
© 2006 Brooks/Cole Thomson
Lectures written by John Kotz
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© 2006 Brooks/Cole - Thomson
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
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© 2006 Brooks/Cole - Thomson
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 spontaneous disintegration of the spontaneous disintegration of some elements into smaller pieces.some elements into smaller pieces.
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© 2006 Brooks/Cole - Thomson
Types of RadiationTypes of Radiation
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© 2006 Brooks/Cole - Thomson
Penetrating AbilityPenetrating Ability
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© 2006 Brooks/Cole - Thomson
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
Both A and Z must be balanced in nuclear reactions.
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© 2006 Brooks/Cole - Thomson
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?
Note that both A and Z are balanced.
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© 2006 Brooks/Cole - Thomson
Nuclear ReactionsNuclear Reactions
• Gamma rays – very high energy waves!Gamma rays – very high energy waves!
-rays are sometimes produced after or emissions.
Radioactive decay generates a new nucleus, but possibly in an unstable configuration of p+, n.
E Nuclear energy levels
A drop in energy level emits a -ray.
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© 2006 Brooks/Cole - Thomson
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
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© 2006 Brooks/Cole - Thomson
Element AbundanceElement Abundance
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© 2006 Brooks/Cole - Thomson
Stability of NucleiStability of NucleiScreens 23.3 and 23.4Screens 23.3 and 23.4
• 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 atom & 99% of mass of H + He = 99.9% of all atom & 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.
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© 2006 Brooks/Cole - Thomson
Half-LifeHalf-LifeSection 15.4 & Screen 23.6Section 15.4 & Screen 23.6
• HALF-LIFEHALF-LIFE is the time it takes for 1/2 a is the time it takes for 1/2 a sample is disappear.sample is 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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© 2006 Brooks/Cole - Thomson
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?
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© 2006 Brooks/Cole - Thomson
Kinetics 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
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© 2006 Brooks/Cole - Thomson
Nuclear FissionNuclear Fission
http://chemincontext.eppg.com/chapter7/FiguresAlive.html
April 26th, 1986 – Chernobyl Disaster
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© 2006 Brooks/Cole - Thomson
Nuclear Nuclear Fission & Fission &
Lise Lise MeitnerMeitner
109109MtMt
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© 2006 Brooks/Cole - Thomson
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.
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© 2006 Brooks/Cole - ThomsonImage from: http://www.animatedsoftware.com/hotwords/nuclear_reactor/nuclear_reactor.htm
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© 2006 Brooks/Cole - Thomson
Radon – a deadly gas?Radon – a deadly gas?
U23892
42Po21884 Pb214
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Ra22688
Pb20682
Rn22286
42Rn22286
Po21884
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More
t1/2 = 3hr
t1/2 = 3d
+
+
+
Rn atoms settle in lungs and eject an particle.
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© 2006 Brooks/Cole - Thomson
Units 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”
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© 2006 Brooks/Cole - Thomson
Effects of RadiationEffects of Radiation
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© 2006 Brooks/Cole - Thomson
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© 2006 Brooks/Cole - Thomson
Nuclear Medicine: Nuclear Medicine: ImagingImaging
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© 2006 Brooks/Cole - Thomson
Nuclear 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.
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© 2006 Brooks/Cole - Thomson
Nuclear 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.
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© 2006 Brooks/Cole - Thomson
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.