Nuclear ChemistryNuclear Chemistry

RadioactivityRadioactivity• Antoine Henri Becquerel

(1852-1908) Discovered radioactivity accidentally while experimenting with photographic film.

RadioactivityRadioactivity

• Discovered polonium Discovered polonium and radiumand radium

• Coined the term Coined the term “radioactivity”“radioactivity”

Marie Curie

(1867-1934)

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

ChangesChanges• Nuclear reactions involve changes in Nuclear reactions involve changes in

the nucleusthe nucleus

• The splitting of the nucleus releases The splitting of the nucleus releases a tremendous amount of energy that a tremendous amount of energy that holds the nucleus together – called holds the nucleus together – called binding energybinding energy

• ““Normal” Chemical Reactions Normal” Chemical Reactions involve involve electronselectrons, not the nucleus, not the nucleus

Types of RadiationTypes of Radiation

e01

He42• AlphaAlpha ( (άά) – a positively ) – a positively

charged helium isotopecharged helium isotope

•BetaBeta ( (ββ) – an electron) – an electron

•GammaGamma ( (γγ) – pure energy; ) – pure energy; called a ray rather than a called a ray rather than a particleparticle 0

0

Other Nuclear ParticlesOther Nuclear Particles

e01

n10• NeutronNeutron

• Positron – a positive Positron – a positive electronelectron

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

A

Z

1n0

neutron0e-1

0-1or

Beta particle0e+1

positron4He2

42or

alpha particle

1

0

0

-1

0

+1

4

2

Symbol Format

Balancing Nuclear ReactionsBalancing Nuclear Reactions•The reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation)

Atomic numbers must balanceand

Mass numbers must balance

Balancing Nuclear Equations

1. Conserve mass number (A).

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

(235 + 1) = 236 (138 + 96 + 2x1) = 236

2. Conserve atomic number (Z) or nuclear charge.

1n0U23592 + Cs138

55 Rb9637

1n0+ + 2

92 + 0 = 55 + 37 + 2x0

23.1

Nuclear ReactionsNuclear Reactions

• Alpha emissionAlpha emission

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

226 ? + 222

88 86RnRa

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 ReactionsNuclear Reactions

• Beta emissionBeta emission

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

238 ? + 238

92 93U Np

238 0 + 23892 -1 93U Np

Other Types of Nuclear Other Types of Nuclear ReactionsReactions

Positron (Positron (00+1+1): a positive electron): a positive electron

Electron capture: Electron capture: the capture of an electron

207 207

Learning Check

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

10B + 4He ? + 1n

5 2 0

Learning Check

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

Artificial Nuclear Artificial Nuclear ReactionsReactions

New elements or new isotopes of known New elements or new isotopes of known elements are produced by bombarding an elements are produced by bombarding an atom with a subatomic particle such as a atom with a subatomic particle such as a proton or neutron -- or even a much proton or neutron -- or even a much heavier particle such as 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 ray is usually emittedusually emitted

Artificial Nuclear Artificial Nuclear ReactionsReactions

Example of a Example of a reaction reaction is is

production of radioactive production of radioactive 3131P for use P for use

in studies of P uptake in the body.in studies of P uptake in the body.

31311515P + P + 11

00n ---> n ---> 32321515P + P +

Transuranium ElementsTransuranium Elements

Elements beyond 92 Elements beyond 92 (transuranium)(transuranium) made made

by starting with a by starting with a 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

Half-LifeHalf-Life

•HALF-LIFEHALF-LIFE is the time that it takes is the time that it takes for 1/2 a sample to decompose.for 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.

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?

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

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 by nuclear reactions initiated by neutrons in cosmic radiationcosmic radiation

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

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

through the biosphere.through 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 = 5730

years.years.

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

Geiger Counter

• Used to detect radioactive substances

Learning Check!

The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

39 hr./13 hr. = 3 half lives

64g x ½ = 32g x ½ = 16g x ½ = 8g will be left after 3 half lives.

0R

64/8 = 8 grams

Nuclear FissionNuclear Fission

Representation of a fission process.

Nuclear Fission & Nuclear Fission & POWERPOWER

• Currently about 103 Currently about 103

nuclear power plants nuclear power plants

in the U.S. and about in the U.S. and about

435 worldwide.435 worldwide.

• 17% of the world’s 17% of the world’s

energy comes from energy comes from

nuclear.nuclear.

Figure 19.6: Diagram of a nuclear power plant.

Nuclear Fusion

Fusion small nuclei combine

2H + 3H 4He + 1n +

1 1 2 0

Occurs in the sun and other stars

Energy

Effects of RadiationEffects of Radiation

Band of Stability Band of Stability and Radioactive and Radioactive DecayDecay

Nuclear Medicine: Nuclear Medicine: ImagingImaging

Thyroid imaging using Tc-99mThyroid imaging using Tc-99m

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.