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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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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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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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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Types of RadiationTypes of Radiation

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Penetrating AbilityPenetrating Ability

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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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• 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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• 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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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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Element AbundanceElement Abundance

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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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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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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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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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Nuclear FissionNuclear Fission

http://chemincontext.eppg.com/chapter7/FiguresAlive.html

April 26th, 1986 – Chernobyl Disaster

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Nuclear Nuclear Fission & Fission &

Lise Lise MeitnerMeitner

109109MtMt

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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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Radon – a deadly gas?Radon – a deadly gas?

U23892

42Po21884 Pb214

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Ra22688

Pb20682

Rn22286

42Rn22286

Po21884

42

More

t1/2 = 3hr

t1/2 = 3d

+

+

+

Rn atoms settle in lungs and eject an particle.

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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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Effects of RadiationEffects of Radiation

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Nuclear Medicine: Nuclear Medicine: ImagingImaging

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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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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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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.

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1 © 2006 Brooks/Cole - Thomson Review Session: –Tuesday C-106 6-8pm