Chapter 20 Nuclear Chemistry Insert picture from First page of chapter

Chapter 20

Nuclear ChemistryInsert picture fromFirst page of chapter

Copyright McGraw-Hill 2009 2

20.1 Nuclei and Nuclear Reactions

• Radioactive decay – emission of particles and/or electromagnetic radiation by unstable nuclei

• Radioactivity - Spontaneous emission of particles or electromagnetic radiation

• Nuclear transmutation, results from the bombardment of nuclei by neutrons, protons, or other nuclei.


Radioactive decay and nuclear transmutation are nuclear reactions, which differ significantly from ordinary chemical reactions.


• The symbols for subatomic particles are as follows:

• In balancing any nuclear equation, we must balance the total of all atomic numbers and the total of all mass numbers for the products and reactants.


Identify X in the following nuclear equation.

017833 XAs


017833 XAs A

Z

reactant mass numbers = product mass numbers

reactant atomic numbers = product atomic numbers

0 78 A

78 A

1)( 33 Z

34 ZTherefore, X is Se or Se78

34


20.2 Nuclear Stability

• Nuclear stability determined by a balance between– Coulombic repulsions– Short range nuclear attractions (very strong)– If replusions > attractions, the nucleus is

unstable– If attractions > replusions, the nucleus is

stable


• Patterns of nuclear stability– Nuclei containing a magic number of protons

and/or neutrons are stable.• The numbers 2, 8, 20, 50, 82, and 126 are

called magic numbers.– There are many more stable nuclei with even

numbers of both protons and neutrons than with odd numbers of these particles.

– All isotopes of the elements with atomic numbers higher than 83 are radioactive.

– All isotopes of technetium (Tc, Z = 43) and promethium (Pm, Z = 61) are radioactive.



particle emission

electron capture

positron emission

Above the belt

Below the belt


• Nuclear Binding Energy– Quantitative measure of nuclear stability– The energy required to break up a nucleus

into its component protons and neutrons.– Represents the conversion of mass to energy

that occurs during an exothermic nuclear reaction.

– The difference between the mass of an atom and the sum of the masses of its protons, neutrons and electrons is called the mass defect.


– According to Einstein’s mass-energy equivalence relationship (E = mc2, where E is energy, m is mass, and c is the velocity of light), the energy released is

– where E and m are defined as follows:

2cm E )(

reactants ofenergy - products ofenergy E

reactants of mass - products of mass m

energy binding nuclear E


nucleons of number

energy binding nuclear nucleon perenergy binding nuclear


Calculate a) the nuclear binding energy in

kilojoules/mol and b) the nuclear binding energy

in joules per nucleon of . The exact atomic

mass of bismuth is 208.9804.

Bi20883

1.008665 nmass 10

1.007825 Hmass 11


amu 83.649475 1.007825 83

amu 126.083125 1.008665 125 amu 209.732600

amu 209.732600- amu 208.9804 m

amu 75220. m

amu 10 6.022

kg 1.00 amu 75220

26. m

a) Nuclear binding energy


2210 s/m kg10 1.12 E

2827 m/s103.00kg 101.2491 E

J 10 1.12 10E

/mol106.022J 10 1.12 2310 E

J/mol10 6.74 13E

kJ/mol10 6.74 13E

kg 101.2491 27m


b) Nuclear binding energy per nucleon

J/nucleon105.38nucleons 208

J10 1.12 13

10

E

kJ/mol10 6.74 energy binding Nuclear 13

kJ/mol10 6.74- 13E


20.3 Natural Radioactivity

• The disintegration of a radioactive nucleus often is the beginning of a radioactive decay series, which is a sequence of nuclear reactions that ultimately result in the formation of a stable isotope.

• The beginning radioactive isotope is called

the parent and the product isotope is called the daughter.


Decay series for uranium-238


• Kinetics of radioactive decay– First-order kinetics (N – number of radioactive

nuclei at time t , k is the rate constant and is the half-life)

– Used as the basis for dating (14C and 238 U are used depending on material)

time atdecay of rate kNt

0

t kt N

Nln

0.693

k t

21 /

21 /

t


A piece of linen cloth found at an ancientburial site is found to have a 14C activity of 4.8 disintegrations per minute. Determinethe age of the cloth. Assume that thecarbon-14 activity of an equal mass of living flax (the plant from which linen ismade) is 14.8 disintegrations per minute. The half-life of carbon-14 is 5715 years.


0

t kt N

Nln

flax living inacitivity C

artifact inactivity C14

14

kt ln

yr101.12 dps 14.8

ps d 4.8ln 14 t

0.693

years5715k

yr101.21 -14 k

yr10 1.0 4t


Uranium-238 Dating

Compare to ratio found in sample.


20.4 Nuclear Transmutation

• Nuclear transmutation differs from radioactive decay in that transmutation is brought about by the collision of two particles.

• Particle accelerators made it possible to synthesize the so-called transuranium elements, elements with atomic numbers greater than 92.


Write an equation for the process represented by

AgpPd 10947

10646 ),(


AgpPd 10947

10646 ),(

emitted particlebombarding particle

p Ag He Pd 11

10947

42

10646



Schematic diagram of a cyclotron particle accelerator.


A particle accelerator uses electric and magnetic fields to increase the kinetic energy of charged species so that a reaction will occur.


20.5 Nuclear Fission

• Nuclear fission is the process in which a heavy nucleus (mass number > 200) divides to form smaller nuclei of intermediate mass and one or more neutrons.

• Because the heavy nucleus is less stable than its products, this process releases a large amount of energy.





• nuclear chain reaction, which is a self-sustaining sequence of nuclear fission reactions.

• critical mass, the minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction.

• Applications of nuclear fission– Atomic bomb– Generation of electricity


Critical Mass: Chain reaction occurs


Schematic diagram of an atomic bomb


Schematic Diagram of a Nuclear Fission Reactor


Refueling the Core of a Nuclear Reactor


• Types of reactors (Using as fuel) – Light water reactor - uses H2O as

moderator used to reduce kinetic energy of neutrons

– Heavy water reactor – uses D2O as moderator• More efficient than light water reactor

– Breeder reactor – produces more fissionable fuel than it uses• Doubling time – time to produce enough

fuel to refuel the original reactor• Can utilize fertile isotopes plutonium-239

and thorium-232

U23592


20.6 Nuclear Fusion

• Nuclear fusion - the combining of small nuclei into larger one– Exempt from waste disposal issues of fission

• Solar fusion

• Thermonuclear reactions – take place at very high temperatures


• Promising reactions

• Technical difficulty – confine nuclei at required temperatures– Magnetic confinement– High-power lasers


Tokamak : A magnetic plasma confinement design


• Used in hydrogen (thermonuclear) bombs– High temperatures attained– Contain solid LiD

– Cleaner than fission bombs


20.7 Use of Isotopes• Chemical analysis

– Use of tracers • Sulfur-35 in the determination of the

structure of thiosulfate

• Photosynthetic pathway using oxygen-18 and 14-carbon


• Isotopes in medicine– Use of tracers for diagnosis

• Sodium-24 – blood flow• Iodine-131 –thyroid conditions• Iodine -123 – brain imaging

– Major advantage – easy to detect

normal Alzheimer victim


Geiger Counter: Used to detect radiation


20.8 Biological Effects of Radiation

• Quantitative measures of radation– curie (Ci): fundamental unit of radioactivity

• Equivalent to 3.70 x 1010 nuclear disintegrations per second

– rad (radiation absorbed dose)• Considers activity• Considers energy• Considers type of radiation emitted• 1 rad = 1 x 105 J/g of tissue irradiated


– RBE (relative biological effectiveness)• Considers biological effect of radiation

–Part of body irradiated–Type of radiation

– rem (roentgen equivalent for man)

• Chemical basis for radiation damage– Ionizing radiation produces radicals– Radicals (free radicals) – molecular

fragments with unpaired electrons



– e and the hydroxyl radical can form other radicals

– In tissues radicals can attack and destroy membranes, enzymes, DNA, etc.

• Radiation damage– Somatic (affect the organism within its

lifetime)– Genetic (inheritable changes and gene

mutations)

Key Points

• Nuclei and nuclear reactions– Radioactive decay– Nuclear transmutations– Particles involved in nuclear reactions– Balancing nuclear reactions

• Nuclear stability– Type of interactions involved– Pattern of stability

• Magic numbers• Odd/even numbers of nucleons

– Nuclear binding energy• Mass defect• Einstein’s mass-energy equivalence

relationship• Calculation nuclear binding energy

–Per mole of nucleons–Per nucleon

• Natural radioactivity– Radioactive decay series

– Kinetics of radioactive decay– Dating based on radioactive decay

• Carbon-14 dating• Uranium-238 dating• Potassium-40 dating

• Nuclear Transmutation– Transuranium element– Particle accelerators

• Nuclear fission– Nuclear fission reactions

• Nuclear chain reactions• Critical mass

– Generation of electric power• Light water reactors• Heavy water reactors• Breeder reactors

– Nuclear fusion• Solar nuclear reactions• Thermonuclear reactions• Potential for generation of electric power• Thermonuclear bombs

• Uses of Isotopes– Chemical Analysis– Medicine

• Biological effects of radiation– Units to measure radiation

• curie• rad• RBE• rem

– Effect of free radicals– Somatic damage– Genetic damage

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Chapter 20 Nuclear Chemistry Insert picture from First page of chapter