1. Chapter 21 Nuclear Chemistry
Lecture Presentation
Chapter 21 Nuclear Chemistry
James F. Kirby
Quinnipiac University
Hamden, CT
© 2015 Pearson Education, Inc.

2. Chemical vs. Nuclear Reactions
Comparison of Chemical Reactions and Nuclear Reactions
Chemical reactions
Nuclear reactions
1. Atoms are rearranged by the breaking and forming of bonds.
2. Only electrons are involved in breaking and forming of bonds.
3. Reactions are accompanied by absorption or release of relatively small amounts of energy.
4. Rates of reaction are influenced by temperature, pressure, concentration, and catalysts.
1. Elements or isotopes are converted from one to another.
2. Protons, neutrons, electrons, and other elementary particles may be involved.
3. Reactions are accompanied by absorption or relase of tremendous amounts of energy.
4. Rates of reaction normally are not affected by temperature, pressure, and catalysts.

3. 21.1 Radioactivity and Nuclear Equations
Some nuclei are instable. They fall apart spontaneously, and emit particles in doing so. The process is called radioactive decay or nuclear decay.
All isotopes of the elements with atomic numbers higher than 84 are radioactive.
Mass Number X A Z
Element Symbol
Atomic Number
Nuclear terminology
proton
neutron
b particle
positron
a particle
1 1 H or 1 1 p
0 1 n
−1 0 e or −1 0 β
+1 0 e or β
2 4 He or 2 4 α A 1 1 4 Z 1 −1 +1 2

4. 21.1 Radioactivity and Nuclear Equations
Conserve mass number (A). U
235 92 + 1n Cs
138 55 + Rb 96 37 +
2 1n = x1
The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.
Conserve atomic number (Z) or nuclear charge. U
235 92 + 1n Cs
138 55 + Rb 96 37 +
2 1n
92 + 0 = x0
The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.

5. EXERCISE #1 212 Po 2 4 α + 82 208 Pb Pb A: 212 = 4 + x x = 208
212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.
212 Po
2 4 α + Pb Pb 84 82
A: 212 = 4 + x
x = 208
Z: 84 = 2 + y
y = 82
EXERCISE #2
Write the balanced equation for the nuclear reaction
26 56 Fe(d,α) Mn where d represents the deuterium nucleus (that is, 1 2 H ).
26 56 Fe +
1 2 H
2 4 α +
25 54 Mn

6. 21.1 Radioactivity and Nuclear Equations
Types of Radioactive Decay
Positron decay
Beta decay
6 11 C B β
6 14 C N + −1 0 β
19 38 K Ar β
19 40 K Ca + −1 0 β
Z: −1
A: unchanged
Z: +1
A: unchanged
(n +1)
(n −1)
Electron-capture decay
Alpha decay
18 37 Ar + −1 0 e Cl
Po Pb α
Inner-orbital electron
Z: −2
A: −4
26 55 Fe + −1 0 e Mn
(n −2)
Z: −1
A: unchanged
(n +1)

7. EXERCISE #3
Which of the following produces a b particle?
a) Ga+ −1 0 e Zn
b) Cu β Ni
c) Fr α At
d) Sb −1 0 β Te
electron-capture decay
positron decay
a decay
b Decay

8. 21.4 Rates of Radioactive Decay
Rate of Decay
Half-life
Time required for the number of nuclides to reach half the original value.
The rate of decay is first-order and proportional to the number of nuclides.
rate = − ∆N ∆t = kN
t1/2 = k
ln N = ln N0 – kt
N = amount of atoms at time t
N0 = amount of atoms at time t = 0
k = decay constant

9. EXERCISE #4
The half-life of molybdenum-99 is 66.0 hrs. How much of a 1.00-mg sample of Mo is left after 330 hrs?
ln N = ln N0 – kt k
t1/2 = k
𝑡 1/2 =
hrs
k =
= hr−1
ln N = ln N0 – kt
= ln(1.00) – ( hr−1)(330 hrs)
= −3.465
N =
e−3.465
= mg

10. 21.3 Nuclear Transmutations
The change of one element into another, brought about by the collision of two particles.
13 27 Al He P n
Cf O Sg n
7 14 N He O p
7 14 N (a, p) 8 17 O

11. 21.7-21.8 Nuclear Power Nuclear fission
A process in which a heavy nucleus (Z >200) splits to form smaller nuclei with intermediate mass and one or more neutrons.
0 1 n U Ba Kr n
Nuclear fusion
A process in which two smaller nuclei combine to form a heavier, more stable nucleus.
2 3 He H He e
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12. 21.7 Nuclear Power: Fission
Nuclear fission
A self-sustaining fission process is called a chain reaction.
Nuclear chain reaction
Event
Neutrons causing fission event
Result
subcritical
< 1
Reaction stops
critical
= 1
Sustained reactions
supercritical
> 1
Violent explosion
Atomic bomb
The TNT was set off first. The explosion forces the section of fissionable material together to form an amount considerably larger than the critical mass.

13. 21.8 Nuclear Power: Fusion Nuclear fusion Fusion Reaction
Energy Released
1 2 H H H H
3.0 x 108 kJ/mol
1 2 H H He n
1.7 x 109 kJ/mol
3 6 Li H He
2.2 x 109 kJ/mol

14. END OF CHAPTER 21