Nuclear Chemistry

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XAZ

Mass Number

Atomic NumberElement Symbol

Atomic number (Z) = number of protons in nucleus

Mass number (A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

A

Z

1p1

1H1or

proton1n0

neutron0e-1

0b-1or

electron0e+1

0b+1or

positron4He2

4a2or

a particle

1

1

1

0

0

-1

0

+1

4

2

23.1

Diagram showing penetrating ability

www.epa.gov

Balancing Nuclear Equations

1. Conserve mass number (A).

The sum of protons plus neutrons in the products must equal

the sum of protons plus neutrons in the reactants.

1n0U23592 + Cs

13855 Rb

9637

1n0+ + 2

235 + 1 = 138 + 96 + 2x1

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

The sum of nuclear charges in the products must equal the

sum of nuclear charges in the reactants.

1n0U23592 + Cs

13855 Rb

9637

1n0+ + 2

92 + 0 = 55 + 37 + 2x023.1

212Po decays by alpha emission. Write the balanced

nuclear equation for the decay of 212Po.

4He2

4a2oralpha particle -

212Po 4He + AX84 2 Z

212 = 4 + A A = 208

84 = 2 + Z Z = 82

212Po 4He + 208Pb84 2 82

23.1

23.1

Nuclear Stability and Radioactive Decay

Beta decay

14C 14N + 0b + n6 7 -140K 40Ca + 0b + n19 20 -1

1n 1p + 0b + n0 1 -1

Decrease # of neutrons by 1

Increase # of protons by 1

Positron decay

11C 11B + 0b + n6 5 +138K 38Ar + 0b + n19 18 +1

1p 1n + 0b + n1 0 +1

Increase # of neutrons by 1

Decrease # of protons by 1

n and n have A = 0 and Z = 023.2

Electron capture decay

Increase # of neutrons by 1

Decrease # of protons by 1

Nuclear Stability and Radioactive Decay

37Ar + 0e 37Cl + n18 17-1

55Fe + 0e 55Mn + n26 25-1

1p + 0e 1n + n1 0-1

Alpha decay

Decrease # of neutrons by 2

Decrease # of protons by 2212Po 4He + 208Pb84 2 82

Spontaneous fission

252Cf 2125In + 21n98 49 023.2

n/p too large

beta decay

X

n/p too small

positron decay or electron capture

Y

23.2

Nuclear Stability

Certain numbers of neutrons and protons are extra stable

n or p = 2, 8, 20, 50, 82 and 126

Like extra stable numbers of electrons in noble gases (e- = 2, 10, 18, 36, 54 and 86)

Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons

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

All isotopes of Tc and Pm are radioactive

23.2

Nuclear binding energy (BE) is the energy required to break

up a nucleus into its component protons and neutrons.

BE + 19F 91p + 101n9 1 0

BE = 9 x (p mass) + 10 x (n mass) 19F mass

E = mc2

BE (amu) = 9 x 1.007825 + 10 x 1.008665 18.9984

BE = 0.1587 amu 1 amu = 1.49 x 10-10 J

BE = 2.37 x 10-11J

binding energy per nucleon = binding energy

number of nucleons

= 2.37 x 10-11 J

19 nucleons= 1.25 x 10-12 J

23.2

Nuclear binding energy per nucleon vs Mass number

nuclear stability

23.2

nuclear binding energy

nucleon

Kinetics of Radioactive Decay

N daughter

rate = -DN

Dtrate = lN

DN

Dt= lN-

N = N0exp(-lt) lnN = lnN0 - lt

N = the number of atoms at time t

N0 = the number of atoms at time t = 0

l is the decay constant

ln2=

tl

23.3

Kinetics of Radioactive Decay

[N] = [N]0exp(-lt) ln[N] = ln[N]0 - lt

[N]

ln [

N]

23.3

Radiocarbon Dating

14N + 1n 14C + 1H7 160

14C 14N + 0b + n6 7 -1 t = 5730 years

Uranium-238 Dating

238U 206Pb + 8 4a + 6 0b92 -182 2 t = 4.51 x 109 years

23.3

Nuclear Transmutation

Cyclotron Particle Accelerator

14N + 4a 17O + 1p7 2 8 1

27Al + 4a 30P + 1n13 2 15 0

14N + 1p 11C + 4a7 1 6 2

23.4

Nuclear Transmutation

23.4

Nuclear Fission

23.5

235U + 1n 90Sr + 143Xe + 31n + Energy92 54380 0

Energy = [mass 235U + mass n (mass 90Sr + mass 143Xe + 3 x mass n )] x c2

Energy = 3.3 x 10-11J per 235U

= 2.0 x 1013 J per mole 235U

Combustion of 1 ton of coal = 5 x 107 J

Nuclear Fission

23.5

235U + 1n 90Sr + 143Xe + 31n + Energy92 54380 0

Representative fission reaction

Nuclear Fission

23.5

Nuclear chain reaction is a self-sustaining sequence of

nuclear fission reactions.

The minimum mass of fissionable material required to

generate a self-sustaining nuclear chain reaction is the

critical mass.

Non-critical

Critical

Schematic Diagram of a Nuclear Reactor

23.5

Annual Waste Production

23.5

35,000 tons SO2

4.5 x 106 tons CO2

1,000 MW coal-fired

power plant

3.5 x 106

ft3 ash

1,000 MW nuclear

power plant

70 ft3

vitrified

waste

Nuclear Fission

23.5

Nuclear Fission

Hazards of the

radioactivities in spent

fuel compared to

uranium ore

From Science, Society and Americas Nuclear Waste, DOE/RW-0361 TG

Chemistry In Action: Natures Own Fission Reactor

Natural Uranium

0.7202 % U-235 99.2798% U-238

Measured at Oklo

0.7171 % U-235

23.6

Nuclear Fusion

2H + 2H 3H + 1H1 1 1 1

Fusion Reaction Energy Released

2H + 3H 4He + 1n1 1 2 0

6Li + 2H 2 4He3 1 2

6.3 x 10-13 J

2.8 x 10-12 J

3.6 x 10-12 J

Tokamak magnetic

plasma

confinement

23.7

Radioisotopes in Medicine

1 out of every 3 hospital patients will undergo a nuclear medicine procedure

24Na, t = 14.8 hr, b emitter, blood-flow tracer

131I, t = 14.8 hr, b emitter, thyroid gland activity

123I, t = 13.3 hr, g-ray emitter, brain imaging

18F, t = 1.8 hr, b+ emitter, positron emission tomography

99mTc, t = 6 hr, g-ray emitter, imaging agent

Brain images

with 123I-labeled

compound

23.7

Radioisotopes in Medicine

98Mo + 1n 99Mo42 0 42

235U + 1n 99Mo + other fission products92 0 42

99mTc 99Tc + g-ray43 43

99Mo 99mTc + 0b + n42 43 -1

Research production of 99Mo

Commercial production of 99Mo

t = 66 hours

t = 6 hours

Bone Scan with 99mTc

Geiger-Mller Counter

23.7

23.8

Biological Effects of Radiation

Radiation absorbed dose (rad)

1 rad = 1 x 10-5 J/g of material

Roentgen equivalent for man (rem)

1 rem = 1 rad x Q Quality Factor

g-ray = 1

b = 1

a = 20

Chemistry In Action: Food Irradiation

Dosage Effect

Up to 100 kilorad

Inhibits sprouting of potatoes, onions, garlics.

Inactivates trichinae in pork. Kills or prevents insects

from reproducing in grains, fruits, and vegetables.

100 1000 kilorads Delays spoilage of meat poultry and fish. Reduces

salmonella. Extends shelf life of some fruit.

1000 to 10,000 kiloradsSterilizes meat, poultry and fish. Kills insects and

microorganisms in spices and seasoning.

Half-lifesThe rate at which a particular radioisotope decays is

described by its half-life.

The half-life is defined as the time that it takes for

one half of a sample of a radioactive element to

decay into another element.

The half-life of a radioisotope is dependent only on

what the radioisotope is.

Table N provides us

with a list of various

nuclides, their decay

modes, and their half-

lifes.

Using Table N, what is

the decay mode and

half-life for Radium-

226?

Using Table N

Table N indicates that Radium-226 undergoes alpha

decay.

Based on this we can write a balanced nuclear equation to

represent this reaction:

This tells us that for every atom of Radium that

decays an atom of Radon is produced.

Using Half-lifeTable N also tells us that Radium-226 has a half-life of

1600 years.

Starting with a 100g

sample, after 1 half-

life (or 1600 years),

50g remain.

After another 1600

years, half of the

50g will remain

(25g).

Carbon-14 Dating

The age of objects that were once alive can be

determined by using the C-14 dating test. In this test,

scientists determine how much C-14 is left in a sample

and from this determine the age of the object.

From Table N we can determine that C-14 undergoes

b decay:

Where does the Carbon-14 come

from?

C-14 is created in the

atmosphere by

cosmic rays.

It becomes part of living

things through

photosynthesis and the

food chain.

When the plant or

animal dies, the C-14

begins to decay.

Using C-14 to Age ObjectsBy comparing the amount of C-14 left in a sample to the amount that

was present when it was alive, and using the half-life of 5700 years

(Table N), one can determine the age of a sample.

Uranium-238 Series

The Uranium-238 Decay Series is used to determine the age of

rocks.

In this series, the

ratio of the U-

238 to the Pb-

206 is used to

determine the

age of the rock.

Parent-daughter Relationship

Aging moon rocks

NASA astronauts have retrieved

842 pounds (382 kg) of moon rocks

(in many missions), which have

been closely studied. The

composition of the moon rocks is

very similar to that of Earth rocks.

Using radioisotope dating, it has

been found that moon rocks are

about 4.3 billion years old.

Sample Half-life Problem 1

A 10 gram of sample of Iodine-131undergoes b decay, what

will be the mass of iodine remaining after 24 days?

From Table N, the life of iodine is determined to be

approximately 8 days.

That means that 24 days is equivalent to 3 half-lifes.

The decay of 10 grams of I-131 would produce:

1.25 grams of I-131 would remain after 24

days.

Sample Half-life Problem 2A sample of a piece of wood is analyzed by C-14 dating. The

percent of C-14 is found to be 25% of what the original C-14

concentration was. What is the age of the sample?

First, lets analyze how many half-lives have taken place.

Two half-lives have gone by while the sample decayed from

the original C-14 concentration to 25% of that concentration.

Based on Table N, the half-life of C-14 is 5730 years,

so

Your turn!

On a sheet of paper, answer the following questions

from your textbook. Indicate how you arrived at your

answer and turn in your work for a homework/quiz

grade.

Page 670

Questions 34 (a and b), 36, 37, 38, 41, 42.

Page 671

Questions 50, 58, 59

The End

This is the end of the first slide show on

nuclear reactions. You may continue

learning about nuclear reactions by viewing

the second show:

Nuclear Chemistry:

Fission and Fusion