Nuclear Chemistry
Chapter 23
23.1-23.6
Nuclear Chemistry
Nuclear Chemistry- the 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 Transmutation- results 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
XAZ
Mass Number
Atomic NumberElement Symbol
Nuclear Reactions
1p11H1or
proton
1n0
neutron
0e-10-1or
electron
0e+10+1or
positron
4He242or
particle
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 + Cs138
55 Rb9637
1n0+ + 2
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.
1n0U23592 + Cs138
55 Rb9637
1n0+ + 2
92 + 0 = 55 + 37 + 2x0
Balancing Nuclear Equations
212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po.
4He242oralpha particle -
212Po 4He + AX84 2 Z
212 = 4 + A A = 208
84 = 2 + Z Z = 82
212Po 4He + 208Pb84 2 82
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 largebeta decay
X
n/p too smallpositron decay or electron capture
Y
Nuclear Stability
Beta decay
14C 14N + 0 + 6 7 -1
40K 40Ca + 0 + 19 20 -1
1n 1p + 0 + 0 1 -1
Decrease # of neutrons by 1
Increase # of protons by 1
23.2
Nuclear Stability
and have A = 0 and Z = 0
1p 1n + 0 + 1 0 +1
Positron decay
11C 11B + 0 + 6 5 +1 Increase # of neutrons by 1
38K 38Ar + 0 + 19 18 +1 Decrease # of protons by 1
Nuclear Stability
Electron capture decay
37Ar + 0e 37Cl + 18 17-1Increase # of neutrons by 1
55Fe + 0e 55Mn + 26 25-1Decrease # of protons by 1
1p + 0e 1n + 1 0-1
Nuclear Stability
Alpha decay
212Po 4He + 208Pb84 2 82 Decrease # of neutrons by 2
Decrease # of protons by 2
Nuclear Binding Energy
Nuclear Binding Energy- the energy required to break up a nucleus into its component protons and neutrons.
Necessity? Mass Defect Einstein’s Theory of Relativity
E = mc2
Nuclear Binding Energy
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
Nuclear Binding Energy
binding energy per nucleon = binding energy
number of nucleons
= 2.37 x 10-11 J19 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
14N + 4 17O + 1p7 2 8 1
Nuclear Transmutation
Notation for reactions First Isotope (bombarding particle, ejected
particle) Final Isotope Notation for Nitrogen-14 bombarded with
particle.
Transuranium Elements
Synthetic elements Atomic Numbers greater than 92 Particle Accelerator necessary for
preparation
Particle Accelerator
Cyclotron Particle Accelerator
Nuclear Fission
Nuclear Fission- the 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
235U + 1n 90Sr + 143Xe + 31n + Energy92 54380 0
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.
Non-critical
Critical
Chain Reaction
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 D2O D absorbs neutrons less efficiently than H Does not require U-235 Neutrons leak out of reactor Expensive to prepare D2O Environmentally friendly
Breeder Reactors
Breeder Reactor- uses 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 Fusion- the 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
