1Chapter 22 - Nuclear Chapter 22 - Nuclear ChemistryChemistry

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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 ofparticles came from the work of Marie CurieMarie Curie (1876-1934).(1876-1934).

• She discovered She discovered radioactive decayradioactive decay, , the spontaneous disintegration of the spontaneous disintegration of some elements into smaller pieces.some elements into smaller pieces.

4Nuclear Reactions vs. Nuclear Reactions vs. Normal Chemical Normal Chemical

ChangesChanges• Nuclear reactions involve the nucleusNuclear reactions involve the nucleus• The protons and neutrons are rearrangedThe protons and neutrons are rearranged• This releases a tremendous amount of energyThis releases a tremendous amount of energy• This energy was used to hold the nucleus This energy was used to hold the nucleus

together and is called together and is called binding energybinding energy

• ““Normal” Chemical Reactions involve Normal” Chemical Reactions involve electronselectrons, not protons and neutrons, not protons and neutrons

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Types of RadiationTypes of Radiation

e01

He42

• Alpha Particle (Alpha Particle (αα) – two protons ) – two protons and two neutrons – a helium nuclei and two neutrons – a helium nuclei with a charge of 2with a charge of 2++

•Beta Particle (Beta Particle (ββ) – an electron) – an electron

•Gamma ray (Gamma ray (γγ) –high energy ) –high energy electromagnetic waves electromagnetic waves 0

0

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Other Nuclear ParticlesOther Nuclear Particles

e01

n10• NeutronNeutron

• Positron – a positive electronPositron – a positive electron

•Electron capture – electron captured Electron capture – electron captured by the nucleus so found on the reactant by the nucleus so found on the reactant side of the equationside of the equation

•Proton – usually referred to as Proton – usually referred to as hydrogen-1hydrogen-1 H11

-1-10 0 ee

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Balancing Nuclear ReactionsBalancing Nuclear Reactions

In the reactants and products

Atomic numbers must balanceand

Mass numbers must balance

Use a particle or isotope to fill in the missing protons and neutrons

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Balancing Nuclear ReactionsBalancing Nuclear Reactions

• Alpha emissionAlpha emission

Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.

Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved

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Balancing Nuclear ReactionsBalancing Nuclear Reactions

• Beta emissionBeta emission

Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.

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Balancing Nuclear ReactionsBalancing Nuclear ReactionsPositron (Positron (00

+1+1): a positive electron): a positive electron

Electron capture: Electron capture: the capture of an electron

207 207

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Learning Check

What radioactive isotope is produced in the following alpha bombardment of boron-10?

105B + 4

2He → ? + 10n

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Learning Check

Nitrogen – 13 plus a neutron is produced by the bombardment of boron?

105B + 4

2He → 137N + 1

0n

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Write Nuclear Equations!

Write the nuclear equation for the beta emitter Co-60.

6027Co 60

28Ni + 0-1β

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Half-Life

• The amount of time that it takes for ½ the mass of a radioactive nuclide to decay.

• Each nuclide has a half-life that is unique to that nuclide

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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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Problem The half life of Polonium-218 is 3.0

minutes. If you begin with 10.0 grams, how much would remain after 9.0 minutes?

Time Mass

0.0 minutes 10.0 grams

3.0 minutes 5.0 grams

6.0 minutes 2.5 grams

9.0 minutes 1.25 grams

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Your Turn• The original mass of P-32 is 4.0 mg. The half-life of

P-32 is 14.3 days. How much P-32 will remain after 57.2 days?

Time Mass 0.0 days 4.0 mg

14.3 days 2.0 mg 28.6 days 1.0 mg 42.9 days .5 mg 57.2 days .25 mg

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Radiocarbon DatingRadiocarbon DatingRadioactive C-14 is formed in the upper atmosphere Radioactive C-14 is formed in the upper atmosphere

by nuclear reactions initiated by neutrons in cosmic by nuclear reactions initiated by neutrons in cosmic radiationradiation

1414N + N + 11oon n 1414C + C + 11HH

The C-14 is oxidized to COThe C-14 is oxidized to CO22, which circulates through , which circulates through

the biosphere.the biosphere.

When a plant dies, the C-14 is not replenished.When a plant dies, the C-14 is not replenished.

But the C-14 continues to decay with tBut the C-14 continues to decay with t1/21/2 = 5730 years. = 5730 years.

Activity of a sample can be used to date the sample.Activity of a sample can be used to date the sample.

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Radiation Exposure• Exposure to radiation can cause cancer and

genetic effects by damaging the DNA.

• Everyone is exposed to environmental background radiation – about .030 to .150 rems is normal

• .500 rems is acceptable according to the U.S. Government.

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Effects of RadiationEffects of Radiation

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Penetrating AbilityPenetrating Ability

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Nuclear FissionNuclear Fission

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Nuclear FissionNuclear Fission• Fission is the splitting of unstable, Fission is the splitting of unstable,

very heavy nuclei into more stable very heavy nuclei into more stable

nuclei of intermediate mass.nuclei of intermediate mass.

• The process produces an enormous The process produces an enormous

amount of energyamount of energy

27Representation of a fission process

28Nuclear 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.

• About 20% of the U. S. About 20% of the U. S.

energy comes from energy comes from

nuclear.nuclear.

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30Diagram of a nuclear power plant

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Nuclear Fusion

Fusion small nuclei combine

2H + 3H 4He + 1n +

1 1 2 0

Occurs in the sun and other stars

Energy

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37Nuclear Medicine: Nuclear Medicine: ImagingImaging

Thyroid imaging using Tc-99Thyroid imaging using Tc-99

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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.