Nuclear chemistry

Nuclear ChemistryNuclear Chemistry

RadioactivityRadioactivity

• One of the pieces of evidence for the fact One of the pieces of evidence for the fact that atoms are made of smaller particles that atoms are made of smaller particles

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

• She discovered radioactivity: the She discovered radioactivity: the spontaneous disintegration of the spontaneous disintegration of the nucleus of some elements into smaller nucleus of some elements into smaller pieces.pieces.

Nuclear Reactions vs. Normal Nuclear Reactions vs. Normal Chemical ChangesChemical Changes

• Nuclear reactions involve the nucleusNuclear reactions involve the nucleus

• The nucleus loses particles, and protons and The nucleus loses particles, and protons and neutrons are rearrangedneutrons are rearranged

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

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

Types of RadiationTypes of Radiation

e01

He42

• Alpha (Alpha (άά) – a positively ) – a positively charged helium isotopecharged 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 (Beta (ββ) – an electron) – an electron

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

00

6Alpha Decay

When a radioactive nucleus emits an alpha particle, a new nucleus forms that has:

• a mass number that is 4 less than that of the initial nucleus.

• an atomic number that is decreased by 2.

7

Alpha Decay Nuclear Equation

Copyright © 2005 by Pearson Education, Inc.Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin CummingsPublishing as Benjamin Cummings

In a balanced nuclear equation, the sum of the mass numbers and the sum of the atomic numbers for the nuclei of the reactant and the products must be equal.

MASS NUMBERS Total = 251 = 251

251Cf 247 Cm + 4 He 98 96 2

Total = 98 = 98

ATOMIC NUMBERS

Balancing Nuclear Equations

Equation for Alpha DecayWrite an equation for the alpha decay of 222Rn.

STEP 1 Write the incomplete equation 222Rn ?s + 4He 86 2

STEP 2 Determine the mass number 222 – 4 = 218

STEP 3 Determine the atomic number 86 – 2 = 84

STEP 4 Determine the symbol of element 84 = Po

STEP 5 Complete the equation

222Rn 218 Po + 4He 86 84 2

10Beta Decay

A beta particle• is an electron

emitted from the nucleus.

• forms when a neutron in the nucleus breaks down.

1n 0e + 1H0 -1 1

STEP 1 Write an equation for the decay of42Potassium,a beta emitter.

42K new nucleus + 0e 19 -1

STEP 2 Mass number : (same) = 42

STEP 3 Atomic number: 19 + 1 = 20

STEP 4 Symbol of element 20 = Ca

STEP 5 42K 42Ca + 0e 19 20 -1

Writing An Equation for Beta Decay

Other Nuclear ParticlesOther Nuclear Particles

e01

n10• NeutronNeutron

• Positron – a positive Positron – a positive electronelectron

• Proton – usually referred Proton – usually referred to as Hydrogento as Hydrogen+1+1

• Any other elemental Any other elemental isotopeisotope

H11

Half Life

The time required for half of the nuclei in a The time required for half of the nuclei in a sample of a specific isotope to undergo sample of a specific isotope to undergo radioactive decay.radioactive decay.

Radioactive Parent

Stable Daughter Half life

Potassium 40 Argon 40 1.25 billion yrs

Rubidium 87 Strontium 87 48.8 billion yrs

Thorium 232 Lead 208 14 billion years

Uranium 235 Lead 207 704 million years

Uranium 238 Lead 206 4.47 billion years

Carbon 14 Nitrogen 14 5730 years

Half Lives for Radioactive Elements

Half Life and radioactive dating

Half-LifeHalf-Life

Decay of 20.0 mg of Decay of 20.0 mg of 1515O. What remains after 3 O. What remains after 3 half-lives? After 5 half-lives?half-lives? After 5 half-lives?

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?

In gamma radiation• energy is emitted from an unstable

nucleus, indicated by m following the mass number.

• the mass number and the atomic number of the new nucleus are the same.

99mTc 99Tc + 43 43

Gamma () Radiation

In position emission,• a proton is converted to a neutron and a

positron.

1 p 1n + 0e 1 0 +1

• the mass number of the new nucleus is the same, but the atomic number decreases by 1.

49Mn 49Cr + 0e 25 24 +1

Positron Emission

Why radiation is dangerous

Radiation ionizes atoms in cell tissue and causes Radiation ionizes atoms in cell tissue and causes chemical reactions akin to decomposition / chemical reactions akin to decomposition / combustion. combustion. disrupts nucleotide sequences (your DNA is mutated)disrupts nucleotide sequences (your DNA is mutated)

Why radiation is dangerousWhy radiation is dangerous

Measuring Radiation•How radioactive a substance is refers to the How radioactive a substance is refers to the number of nuclear disintegrations per second number of nuclear disintegrations per second that occur in a sample. that occur in a sample.

•SI unit is the Becquerel (Bq) which is 1 SI unit is the Becquerel (Bq) which is 1 disintegration/seconddisintegration/second

•The older unit, the Curie(Ci) :The older unit, the Curie(Ci) :1 Ci = 3.7 x 101 Ci = 3.7 x 101010 disintegrations per second disintegrations per second

Measuring Radiation

•The The 'rad'rad' is used to describe the energy quantity ' is used to describe the energy quantity or dose of radiation absorbed. or dose of radiation absorbed.

•radrad (rd) stands for “radiation absorbed dose” (rd) stands for “radiation absorbed dose”

•One One radrad defined as 10 defined as 10-5-5 J/g of material. J/g of material.

Measuring Radiation Damage

•The rad does not account for the kind of damage The rad does not account for the kind of damage done, only for how much radiation goes in.done, only for how much radiation goes in.

•To take into account this fact the REM was To take into account this fact the REM was derivedderived

•To find the dose in REMS the dosage in rads is To find the dose in REMS the dosage in rads is multiplied by a conversion factor that reflects the multiplied by a conversion factor that reflects the effectiveness of the effectiveness of the kindkind of radiation causing the of radiation causing the damagedamage

Dosage in REMS Biological Effect : 25    notable change in blood cell components 25    notable change in blood cell components  100  radiation sickness - nausea, vomiting, 100  radiation sickness - nausea, vomiting, decrease in white blood cell count, diarrhea, decrease in white blood cell count, diarrhea, dehydration, prostration, hemorrhaging and loss dehydration, prostration, hemorrhaging and loss of hair of hair  200  the same as above but more pronounced in a 200  the same as above but more pronounced in a shorter period of time shorter period of time 

400  ½ of any population exposed to this dosage 400  ½ of any population exposed to this dosage will be dead in 60 days will be dead in 60 days 

600  all exposed to this level will be dead in one 600  all exposed to this level will be dead in one week week 

Chernobyl

Anyone near the Chernobyl plant when it melted Anyone near the Chernobyl plant when it melted down received 400 rems also immediately. down received 400 rems also immediately.

The day after 1 rem/hr was found in the nearest The day after 1 rem/hr was found in the nearest city. city.

Normal background radiation is 1,000 times lower Normal background radiation is 1,000 times lower than thisthan this

Detecting radiation

Detecting radiation

Protection from radiation•Wear lead infused suit.Wear lead infused suit.•Keep your distance.Keep your distance.• Inverse square law.Inverse square law.• Intensity of radiation is inversely proportional Intensity of radiation is inversely proportional to the square of the distance from the sourceto the square of the distance from the source

Nuclear Fuel

Uranium “Yellow Cake” UUranium “Yellow Cake” U33OO88

FissionNeutronNeutron

Fission Chain Reaction

Representation of a fission process.

Nuclear FissionNuclear Fission

Diagram of a nuclear power plant.

Nuclear Fission & POWERNuclear Fission & POWER

• 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.

Fusion

• A process by which multiple like-charged atomic nuclei join together to form a heavier nucleus

Nuclear Fusion

Fusion: small nuclei combine

2H + 3H 4He + 1n +

1 1 2 0

Occurs in the sun and other stars

Energy

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

10B + 4He ? + 1n

5 2 0

Fusion

Nuclear Fusion

Fusion • Excessive heat can not be

contained• Attempts at “cold” fusion have

FAILED.• “Hot” fusion is difficult to contain

Artificial Nuclear ReactionsArtificial Nuclear Reactions

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 heavier proton or neutron -- or even a much heavier particle such as particle such as 44He and He and 1111B.B.

Reactions using neutrons are called Reactions using neutrons are called

reactionsreactions because a because a ray is usually ray is usually emitted.emitted.

Radioisotopes used in medicine are often made Radioisotopes used in medicine are often made by by reactionsreactions..

Artificial Nuclear ReactionsArtificial Nuclear Reactions

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

starting with a starting with a reactionreaction

2382389292U + U + 11

00n ---> n ---> 2392399292U + U +

2392399292U U ---> ---> 239239

9393Np + Np + 00-1-1

2392399393Np Np ---> ---> 239239

9494Pu + Pu + 00-1-1

Nuclear Medicine: ImagingNuclear Medicine: Imaging

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.