1. Chemistry: Atoms First Second Edition Julia Burdge & Jason Overby
Chapter 20
Nuclear Chemistry
M. Stacey Thomson
Pasco-Hernando State College 1
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. What Is Radioactivity?
Radioactivity is the release of tiny, high- energy particles or gamma rays from an atom
Particles are ejected from the nucleus
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3. Nuclear Decay
Some nuclei are unstable, and will, over time, emit particles and/or electromagnetic radiation until they become stable.
The spontaneous emission of particles or electromagnetic radiation is known as radioactivity.
All elements with Z > 83 are radioactive.
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4. Nuclei and Nuclear Reactions
20.1
During a nuclear reaction, the products and reactants will contain different elements as the nuclei change.
There are several types of particles or forms of electromagnetic radiation that may be emitted during a nuclear reaction.
You should learn the names, symbols and the mass number and charge of each of the particles.

5. Nuclei and Nuclear Reactions
The symbols for subatomic particles include:
proton
neutron
electron
positron
α particle

6. Nuclei and Nuclear Reactions
In balancing a nuclear reaction, simply balance the total of all atomic numbers and total of all mass numbers for the products and reactants. +
Mass number:
212
= 212
Atomic number: 84
= 84

7. Example 20.1
Identify the missing species X in each of the following nuclear equations:
(a)
(b)
(c)

8. Nuclear Stability
20.2
Review the information from Chapter 2 on Nuclear stability.
Principle factor for nuclear stability is neutron-to-proton
ratio (n/p)
There are more stabile nuclei with 2, 8, 20, 50, 82, or 126 protons or neutrons
More with even #’s
All with atomic number > 83 are radioactive
All isotopes of Tc and Pm are radioactive

9. Nuclear Stability
The figure shows the number of neutrons vs. the number of protons in various isotopes.
Stable nuclei are located in an area of the graph known as the belt of stability.
Most radioactive nuclei lie outside the belt.
Above the belt of stability, the nuclei have higher neutron-to-proton ratio.

10. Types of Nuclear Decay
Above the belt, isotopes decay by:
beta emission

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12. Types of Nuclear Decay
Below the belt, isotopes decay by:
positron emission
electron capture

13. A Low Neutron to Proton Ratio
If the N/Z ratio is too low, and the nuclide has too many protons. These nuclides tend to undergo either positron emission or electron capture.
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14. Positron Emission
Positrons result from a proton changing into a neutron.
A positron has a charge of +1 and negligible mass.
anti-electron
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15. Positron Emission When an atom loses a positron from the nucleus, its
mass number remains the same
atomic number decreases by 1
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17. Electron Capture
Electron capture occurs when an inner orbital electron is pulled into the nucleus. A
proton combines with the electron to make a neutron. This decreases the atomic number, and increases the N/Z ratio.
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18. Electron Capture As a result of electron capture:
mass number stays the same
atomic number decreases by one
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19. Particle Changes
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20. Alpha (α) Emission
Many nuclides that are too heavy to be stable (Z>83) undergo alpha emission. An  particle contains 2 protons and 2 neutrons, and is the same as a helium nucleus.
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22. Alpha Emission Loss of an alpha particle means:
atomic number decreases by 2
mass number decreases by 4
As a result, the N/Z ratio increases.
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23. Gamma (γ) Emission
During a nuclear reaction, high energy electromagnetic radiation, called gamma rays, is often emitted. Generally occurs after the nucleus undergoes some other type of decay and the remaining particles rearrange.
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24. Gamma Emission Gamma (g) rays are high energy photons of light
No loss of particles from the nucleus
No change in the composition of the nucleus
same atomic number and mass number
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25. Other Properties of Radioactivity
Radioactive rays can ionize matter
cause uncharged matter to become charged
basis of Geiger Counter and electroscope
Radioactive rays have high energy
Radioactive rays can penetrate matter
Radioactive rays cause phosphorescent chemicals to glow
basis of scintillation counter
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26. Penetrating Ability of Radioactive Rays
0.01 mm mm mm
Pieces of Lead
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27. Ionizing Ability of Radiation
Highly energetic radiation interacts with molecules and atoms by ionizing them. This can have serious biological effects on cells in living systems. Cell damage, or abnormal cell replication can occur.
α particles are highly ionizing, but not very penetrating. They can be stopped by a sheet of paper, clothing, or air. As a result, they are not very damaging unless ingested or breathed into the lungs.
β particles have lower ionizing power, but are more penetrating. A sheet of metal or a thick piece of wood will stop them.
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28. Ionizing Ability of Radiation
γ rays have the lowest ionizing power, but are the most penetrating. Several inches of lead or slabs of concrete are needed to stop gamma rays.
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29. Nuclear Binding Energy
A quantitative measure of nuclear stability is the nuclear binding energy.The nuclear binding energy is the energy required to break up a nucleus into its component protons and neutrons.
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.
The measured mass of 19F = amu
mass of 9 protons = 9 x amu = amu
mass of 9 electrons = 9 x x10-4 amu = amu
mass of 10 neutrons = 10 x amu = amu
The calculated mass of 19F = amu
Mass defect of 19F = amu – amu = amu

30. Nuclear Binding Energy
The loss in mass is converted to energy and can be quantified with Einstein’s mass-energy equivalence relationship.
ΔE = energy of product – energy of reactant
Δm = mass of product – mass of reactant
ΔE = (Δm)c2
For 19F, Δm = – amu = – amu

31. Nuclear Binding Energy
The loss in mass is converted to energy and can be quantified with Einstein’s mass-energy equivalence relationship.
ΔE = (Δm)c2
ΔE = (– x 10–28 kg)( x 108 m/s)2
ΔE = – x 10–11 kg (m/s)2
ΔE = – x 10–11 J

32. Nuclear Binding Energy
Plot of nuclear binding energy per nucleon versus mass number.

33. Nuclear Radioactivity
20.3
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.

34. Kinetics of Radioactive Decay
All radioactive decays obey first-order kinetics.
The corresponding half-life of the reaction is given by:

35. Nuclear Radioactivity
A piece of linen cloth found at an ancient burial site is found to have a 14C activity of 4.8 disintegrations per minute. Determine the age of the cloth.
Assume that the carbon-14 activity of an equal mass of living flax (the plant from which linen is made) is 14.8 disintegrations per minute. The half-life of carbon-14 is 5715 years.
Solution
Step 1: Determine the rate constant from the equation below:

36. Dating Based on Radioactive Decay
A piece of linen cloth found at an ancient burial site is found to have a 14C activity of 4.8 disintegrations per minute. Determine the age of the cloth.
Assume that the carbon-14 activity of an equal mass of living flax (the plant from which linen is made) is 14.8 disintegrations per minute. The half-life of carbon-14 is 5715 years.
Solution
Step 2: Use the equation below to calculate time:
t = 1.0 x 104 yr

37. 14C activity in fresh-cut wood
Worked Example 20.3
A wooden artifact is found to have a 14C activity of 9.1 disintegrations per second. Given that the 14C activity of an equal mass of fresh-cut wood has a constant value of 15.2 disintegrations per second, determine the age of the artifact. The half-life of carbon-14 is 5715 years.
Strategy The activity of a radioactive sample is proportional to the number of radioactive nuclei. Thus, we can use ln([A]t/[A]0) = –kt with activity in place of concentration:
ln = –kt
To determine k, though, we must solve t½ = 0.693/k, using the value of t½ for carbon-14 (5715 years) given in the problem statement.
14C activity in artifact
14C activity in fresh-cut wood

38. Nuclear Transmutation
20.4
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. +

39. Nuclear Transmutation
Write an equation for the process represented by:
Solution
Step 1: Determine the bombarding particle and the emitted particle:
Step 2: Write the equation:
emitted particle
bombarding particle

40. Worked Example 20.5
Write the balanced nuclear equation for the reaction represented by where d represents a deuterium nucleus.
Strategy The species written first is a reactant. The species written last is a product. Within the parentheses, the bombarding particle (a reactant) is written first, followed by the emitted particle (a product).
Solution The bombarding and emitted particles are represented by and , respectively.
Think About It Check your work by summing the mass numbers and atomic numbers on both sides of the equation.

41. Nuclear Transmutation
Schematic of a cyclotron particle accelerator.

42. Nuclear Transmutation
Section of a particle accelerator.

43. Nuclear Fission
20.5
Nuclear fission is the process in which a heavy nucleus (mass number > 200) divides to form smaller nuclei and one or more neutrons. +

44. Nuclear Fission
Relative yields of the products resulting from the fission of 235U as a function of mass number.

45. Nuclear Fission
235U is capable of a self-sustaining sequence of nuclear fission known as a nuclear chain reaction.

46. Nuclear Fission
The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass.

47. Nuclear Fission
Schematic of a nuclear fission reactor.

48. Nuclear Fusion
20.6
Nuclear fusion is the process of combining small nuclei into larger ones.
The following reactions are believed to take place in the sun:
Because fusion reactions take place at very high temperatures, they are often called thermonuclear reactions.

49. Nuclear Fusion
Promising fusion reactions include:
Due to the high temperature
requirements, containment
is an issue.

50. Nuclear Fusion
A promising design employs high power lasers
A small scale fusion reaction was carried out at the Lawrence Livermore National Laboratory (right)
Technical difficulties still need to be overcome before it can be put to practical use

51. Use of Isotopes: Chemical Analysis
20.7
Radioactive and stable isotopes have applications in science for molecular structure determination.
Two proposed structures for thiosulfate ion:
By using radioactive sulfer-35 isotope, the isotope acts as a “label” for the S atoms.
Based on studies, structure 2 has been confirmed. 1) 2)

52. Isotopes in Medicine
Radioactive and stable isotopes have applications in science and medicine.
Radioactive isotopes are used as tracers.
Use of tracers for diagnosis include:
Sodium-24 – blood flow
Iodine-131 –thyroid conditions
Iodine-123 – brain imaging

53. Biological Effects of Radiation
20.8
The fundamental unit of radioactivity is the curie (Ci)
1 Cu = 3.70 x 1010 disintegrations per second.

54. Biological Effects of Radiation
A common unit for the absorbed dose of radiation is the rad (radiation absorbed dose).
1 rad = 1 x 105 J/g of tissue irradiated
The rem (roentgen equivalent for man) is determined from the number of rads:
Number of rems = number of rads x 1 RBE
RBE = the relative biological effectivness.

55. Biological Effects of Radiation