Nuclear Chemistry
Chapter 23
23.1-23.6

Nuclear Chemistry
 Nuclear Chemistrythe study of reactions involving changes in atomic nuclei.
 Importance
 Disadvantages

Nuclear Reactions





Except for Hydrogen, all nuclei contain particles called protons and neutrons.
Nuclei can be stable or unstable.
Unstable Nuclei emit particles and/or electromagnetic radiation spontaneously.
Phenomenon is called Radioactivity.
Nuclear Transmutationresults from the bombardment of nuclei by neutrons, protons or other nuclei.

Nuclear Reactions


Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Mass Number
Atomic Number
A
Z
X Element Symbol

Nuclear Reactions proton
1
1 p or
1
1 H neutron
1
0 n
0
-1 electron e or
-1
0 b positron
0
+1 e or
+1
0 b
4
2 a particle
He or
2
4 a

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.
235
92
U + 1
0 n 138
55
Cs +
96
37
Rb + 2 1
0 n
235 + 1 = 138 + 96 + 2x1

Balancing Nuclear Equations
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.
235
92
U + 1
0 n 138
55
Cs +
96
37
Rb + 2 1
0 n
92 + 0 = 55 + 37 + 2x0

Balancing Nuclear Equations
212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po.
alpha particle -
4
2
He or
4
2 a
212
84
Po 4
2
He + A
Z
X
212 = 4 + A
84 = 2 + Z
A = 208
Z = 82
212
84
Po 4
2
He + 208
82
Pb

Chemical Reactions vs. Nuclear
Reactions

Nuclear Stability
 Nucleus is very small
 Contributes most of weight of atom
 Extremely high density
 Even higher # of particles

Nuclear Stability
 Particles repel/attract each other
 neutron-to-proton ratio
 Predicting stability:
– Magic numbers: 2,8,20,50,82,126
–
–
–
Even numbers of neutrons and protons vs. odd numbers
All isotopes of elements with atomic numbers higher than 83 are radioactive.
All isotopes of Tc and Pm are radioactive.

n/p too large beta decay
X
Y n/p too small positron decay or electron capture

Nuclear Stability
Beta decay
14
6
C 14 N + 0 b
+ n
7 -1
40
19
K 40 Ca + 0 b
+ n
20 -1
Decrease # of neutrons by 1
Increase # of protons by 1
1
0 n 1 p + 0 b
+ n
1 -1
23.2

Nuclear Stability
Positron decay
11
6
C 11 B + 0 b
+ n
5 +1
Increase # of neutrons by 1
38
19
K 38 Ar + 0 b
+ n
18 +1
Decrease # of protons by 1
1
1 p 1 n + 0 b
+ n
0 +1 n and n have A = 0 and Z = 0

Nuclear Stability
Electron capture decay
37
18
Ar + 0 e 37 Cl + n
-1 17
55
26
Fe + 0 e 55 Mn + n
-1 25
Increase # of neutrons by 1
Decrease # of protons by 1
1
1 p + 0 e 1 n + n
-1 0

Nuclear Stability
Alpha decay
212
84
Po 4
2
He + 208
82
Pb Decrease # of neutrons by 2
Decrease # of protons by 2

Nuclear Binding Energy
 Nuclear Binding Energythe energy required to break up a nucleus into its component protons and neutrons.
 Necessity?


Mass Defect
Einstein’s Theory of Relativity
E = mc 2

Nuclear Binding Energy
E = mc 2
BE + 19
9
F 9 1
1 p + 10 1
0 n
BE = 9 x (p mass) + 10 x (n mass) – 19 F mass
BE (amu) = [(9 x 1.007825) + (10 x 1.008665)] – 18.9984
BE = 0.1587 amu
BE = 2.37 x 10 -11 J
1 amu = 1.49 x 10 -10 J

Nuclear Binding Energy binding energy per nucleon = binding energy number of nucleons
=
2.37 x 10 -11 J
19 nucleons
= 1.25 x 10 -12 J

Nuclear Binding Energy

Natural Radioactivity
 Outside the belt of stability, nuclei are radioactive.
 Radioactive nuclei spontaneously emit radiation.
–
α particles, β particles, γ rays, etc.
 Disintegration of radioactive nucleus leads to a decay series.

Radioactive Decay--Dating




Uranium decay
After time, half of parent exsists
Equal amounts of parent and daughter
Age?

Nuclear Transmutations
 Rutherford, 1919


Artificial Radioactivity
Nitrogen bombarded by α particles
14
7
N + 4 a
2
17 O + 1 p
8 1

Nuclear Transmutation
 Notation for reactions


First Isotope (bombarding particle, ejected particle) Final Isotope
Notation for Nitrogen-14 bombarded with a particle.

Transuranium Elements
 Synthetic elements
 Atomic Numbers greater than 92
 Particle Accelerator necessary for preparation

Particle Accelerator
Cyclotron Particle Accelerator

Nuclear Fission
 Nuclear Fissionthe process in which a heavy nucleus (mass number > 200) divides to form smaller nuclei of intermediate mass and one or more neutrons.
 Energy is released.
 Uranium-235 was the first element discovered to go through nuclear fission.

Nuclear Fission
235
92
U + 1
0 n 90
38
Sr + 143
54
Xe + 3 1
0 n + Energy

Nuclear Fission
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 .

Chain Reaction
Non-critical
Critical

The Atomic Bomb

Nuclear Reactors
 Peaceful application of nuclear fission
 Generates electricity from chain reactions
 Provides 20% of electricity in U.S.
 Light water reactors; Heavy water reactors;
Breeder reactors

Light Water Reactors








Most U.S. nuclear reactors are light water
Light Hydrogen
Use Uranium-235 under controlled conditions
Releases large quantities of steam
Steam drives electric generators
Needs large amounts of coolant
Plants built by lakes and rivers
Large amounts of thermal pollutant

Light Water Reactors

Heavy Water Reactors


Uses Deuterium D
2
O
D absorbs neutrons less efficiently than H
 Does not require U-235
 Neutrons leak out of reactor


Expensive to prepare D
2
O
Environmentally friendly

Breeder Reactors





Breeder Reactoruses uranium fuel, but unlike a conventional nuclear reactor, it produces more fissionable materials than it uses.
Converts uranium-238 to plutonium-239 in a 3 step process.
Plutonium-239 undergoes fission
Reactor produces 1 mole of p-239 for every 1 mole used.
Takes 7-10 years for complete regeneration.

Hazards of Nuclear Energy
 Production of radioactive isotopes with long half-lives (24,400 years)
 Radioactive and toxic substances
 Three-mile Island Reactor- radiation escaped
 Chernobyl Nuclear Plant- fire and explosion
 Accidents
 Waste Disposal

Nuclear Fusion
 Nuclear Fusionthe combining of small nuclei into larger ones.
 Two small nuclei can combine and release large amounts of energy
 To occur, the nuclei must be in an environment with high temperature.
 Thermonuclear Reactions
 Nuclear fusion occurs constantly on the Sun.

Nuclear Fusion
 How do we get it to occur?
 Container?

The Hydrogen Bomb
 Thermonuclear Bomb
 All power and no control
 Fusion reaction then fission reaction
 Fusion reaction creates high temp. for fission reaction
 Bombs usually contain Co-59 and upon explosion convert to Co-60