# Nuclear Chemistry: The Heart of Matter

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Nuclear Chemistry: The Heart of Matter
Chemistry for Changing Times 10th edition Hill/Kolb Chapter 4 Nuclear Chemistry: The Heart of Matter Daniel Fraser University of Toledo, Toledo OH ©2004 Prentice Hall

Types of Radiation Ionizing radiation – knocks electrons out of atoms or groups of atoms Produces charged species – ions Charged species that cause damage Chapter 4

Differences Between Chemical and Nuclear Reactions
Chapter 4

Half-Life Period for one-half of the original elements to undergo radioactive decay Characteristic for each isotope Fraction remaining = n = number of half-lives Chapter 4

Practice Problems Chapter 4

Radioisotopic Dating Use certain isotopes to estimate the age of various items 235U half-life = 4.5 billion years Determine age of rock 3H half-life = 12.3 years Used to date aged wines Chapter 4

Chapter 4 1 April 2017 04-TB05 Title:
Table 4.5 Several Isotopes Useful in Radioactive Dating Caption: Isotopes commonly used to determine the age of matter. Note the range limitations for each isotope. Notes: Carbon-14 dating is the most commonly recognized dating procedure. Chapter 4 Chapter 4

Carbon-14 Dating 99.9% 12C Produce 14C in upper atmosphere
Half-life of 5730 years ~50,000 y maximum age for dating Chapter 4

Example 4.2 Half-Lives Solution Exercise 4.2A Exercise 4.2B
You obtain a new sample of cobalt-60, half-life 5.25 years, with a mass of 400 mg. How much cobalt-60 remains after years (three half-lives)? Solution The fraction remaining after three half-lives is 1 2n 23 2 x 2 x 2 8 = The amount of cobalt-60 remaining is ( ) (400 mg) = 50 mg. You have mg of freshly prepared gold-189, half-life 30 min. How much of the gold-189 sample remains after five half-lives? Exercise 4.2A What percentage of the original radioactivity remains after five half-lives? Exercise 4.2B Chapter 4

Example 4.3 Solution Exercise 4.3A Exercise 4.3B
You obtain a 20.0-mg sample of mercury-190, half-life 20 min. How much of the mercury-190 sample remains after 2 hr? There are 120 min in 2 hr. There are ( ) = 6 half-lives in 2 hr. The fraction remaining after six half-lives is The amount of mercury-190 remaining is ( ) (20.0 mg) = mg. Solution 1 2n 26 2 x 2 x 2 x 2 x 2 x 2 64 = 120 20 A sample of 16.0 mg of nickel-57, half-life 36.0 hr, is produced in a nuclear reactor. How much of the nickel-57 sample remains after 7.5 days? Exercise 4.3A Tc-99 decays to Ru-99 with a half-life of 210,000 years. Starting with 1.0 mg of Tc-99, how long will it take for 0.75 mg of Ru-99 to form? Exercise 4.3B Chapter 4

( ) Example 4.4 Solution Exercise 4.4
A piece of fossilized wood has carbon-14 activity one-eighth that of new wood. How old is the artifact? The half-life of carbon-14 is 5730 years. Solution The carbon-14 has gone through three half-lives: It is therefore about 3 x 5730 = 17,190 years old. 1 8 = 2 x ( ) 3 How old is a piece of cloth that has carbon-14 activity that of new cloth fibers? The half-life of carbon-14 is 5730 years. Exercise 4.4 1 16 Chapter 4

Shroud of Turin Alleged burial shroud of Jesus Christ
Contains faint human likeness First documented in Middle Ages Carbon-14 dating done in 1988 Three separate labs Shroud ~800 years old Unlikely to be burial shroud Chapter 4

Uses of Radioisotopes Tracers Agriculture Easy to detect
Different isotopes have similar chemical and physical properties Physical, chemical, or biological processes Agriculture Induce heritable genetic alterations – mutations Preservative Destroys microorganisms with little change to taste or appearance of the food Chapter 4

Nuclear Medicine Used for two purposes
Therapeutic – treat or cure disease using radiation Diagnostic – obtain information about patient’s health Chapter 4

Makes some forms of cancer susceptible Try to destroy cancer cells before too much damage to healthy cells Direct radiation at cancer cells Gives rise to side effects Chapter 4

Diagnostic Uses Many different isotopes used
See Table 4.6 Can measure specific things Iodine-131 to locate tumors in thyroid Selenium-75 to look at pancreas Gadolinium-153 to determine bone mineralization Chapter 4

Imaging Positron emission tomography (PET)
Uses an isotope that emits a positron Observe amount of radiation released Chapter 4

Chapter 4 1 April 2017 04-TB06 Title:
Table 4.6 Some Radioisotopes and Their Medical Applications Caption: Isotopes used for diagnosis and therapy in the medical field. Notes: Note that most isotopes have relatively short half-lives. Chapter 4 Chapter 4

The more mass the particle has, the less penetrating it is The faster the particle is, the more penetrating it is Chapter 4

To minimize damage Stay a distance from radioactive sources Use shielding; need more with more penetrating forms of radiation Chapter 4

Energy from Nucleus E = mc2 Lose mass, gain energy
For chemical reactions, mass changes are not measurable For nuclear reactions, mass changes may be measurable Chapter 4

Binding Energy Holds protons and neutrons together in the nucleus
The higher the binding energy, the more stable the element Chapter 4

Nuclear Fission “Splitting the atom”
Break a large nucleus into smaller nuclei Chapter 4

Nuclear Chain Reaction
Neutrons from one fission event split further atoms Only certain isotopes, fissile isotopes, undergo nuclear chain reactions Chapter 4

Manhattan Project How to sustain the nuclear reaction?
How to enrich uranium to >90% 235U? Only 0.7% natural abundance How to make 239Pu (another fissile isotope)? How to make a nuclear fission bomb? Chapter 4

Radioactive Fallout Nuclear bomb detonated; radioactive materials may rain down miles away and days later Some may be unreacted U or Pu Radioactive isotopes produced during the explosion Chapter 4

Nuclear Power Plants Provide ~20% U.S. electricity
France >70% Slow controlled release of energy Need 2.5–3.5% 235U Problem with disposal of radioactive waste Chapter 4

Nuclear Fusion Reaction takes smaller nuclei and builds larger ones
Also called thermonuclear reactions Releases tremendous amounts of energy 1 g of H would release same as 20 tons of coal Chapter 4

End of Chapter 4 Chapter 4

Nuclei that undergo radioactive decay May produce one or more types of radiation Chapter 4

Background radiation What occurs from natural sources >80% of radioactivity exposure Chapter 4

Nuclear Equations Elements may change in nuclear reactions
Total mass and sum of atomic numbers must be the same MUST specify isotope Chapter 4

Alpha Decay Nucleus loses  particle
Mass decreases by 4 and atomic number decreases by 2 Chapter 4

Beta Decay Nucleus loses  particle
No change in mass but atomic number increases Chapter 4

Positron Emission Loses a positron
Equal mass but opposite charge of an electron Decrease in atomic number and no change in mass + Chapter 4

Electron Capture Nucleus absorbs an electron and then releases an X-ray Mass number stays the same and atomic number decreases Chapter 4

Gamma Radiation Release of high-energy photon
Typically occurs after another radioactive decay No change in mass number or atomic number Chapter 4

Artificial Transmutation
Transmutation changes one element into another Middle Ages: change lead to gold In 1919 Rutherford established protons as fundamental particles Basic building blocks of nuclei Chapter 4

Example 4.1 Balancing Nuclear Equations
Write balanced nuclear equations for each of the following processes. In each case, indicate what new element is formed. a. Plutonium-239 emits an alpha particle when it decays. b. Protactinium-234 undergoes beta decay. c. Carbon-11 emits a positron when it decays. d. Carbon-11 undergoes electron capture. Solution a. We start by writing the symbol for plutonium-239 and a partial equation showing that one of the products is an alpha particle (helium nucleus): 239 94 Pu 4 2 He + ? Mass and charge are conserved. The new element must have a mass of 239 – 4 = 235 and a charge of 94 – 2 = 92. The nuclear charge (atomic number) of 92 identifies the element as uranium (U): He + 235 92 U Chapter 4

Example 4.1 Balancing Nuclear Equations (cont.)
b. Write the symbol for protactinium-234 and a partial equation showing that one of the products is a beta particle (electron): 234 91 Pa –1 e + ? The new element still has a mass number of 234. It must have a nuclear charge of 92 in order for the total charge to be the same on each side of the equation. The nuclear charge identifies the new atom as another isotope of uranium (U): 234 91 Pr –1 e + 92 U c. Write the symbol for carbon-11 and a partial equation showing that one of the products is a positron: 11 6 C +1 e + ? To balance the equation, a particle with a mass number of 11 and an atomic number of 5 (B) is required: e + 5 B Chapter 4

Example 4.1 Balancing Nuclear Equations (cont.)
11 6 C –1 e d. We write the symbol for carbon-11 and a partial equation showing it capturing an electron: + ? 11 6 C –1 e 5 B To balance the equation, the product must have a mass number of 11 and an atomic number of 5 (B): + As mentioned in the text, positron emission and electron capture result in identical changes in atomic number, and therefore the identical elements are formed! Also, as parts (c) and (d) illustrate, C-11 (and certain other nuclei) can undergo several different types of radioactive decay processes. Write balanced nuclear equations for each of the following processes. In each case, indicate what new element is formed. Exercise 4.1 a. Radium-226 decays by alpha emission. b. Sodium-24 undergoes beta decay. c. Gold-188 decays by positron emission. d. Argon-37 undergoes electron capture. Chapter 4

Example 4.5 Solution Exercise 4.5
When potassium-39 is bombarded with neutrons, chlorine-36 is produced. What other particle is emitted? Cl + ? 36 17 1 n 39 19 K + Solution Write a balanced nuclear equation. To balance the equation, we need four mass units and two charge units (that is, a particle with a nucleon number of 4 and an atomic number of 2). That’s an alpha particle. Cl + 36 17 1 n 39 19 K + He 4 2 Technetium-97 is produced by bombarding molybdenum-96 with a deuteron (hydrogen-2 nucleus). What other particle is emitted? Exercise 4.5 Tc + ? 97 43 2 1 H 96 42 Mo + Chapter 4

Example 4.6 Solution Exercise 4.6
One of the isotopes used for PET scans is oxygen-15, a positron emitter. What new element is formed when oxygen-15 decays? Solution First write the nuclear equation +1 e + ? 15 8 O The nucleon number does not change, but the atomic number becomes 8 – 1, or 7; and so the new product is nitrogen-15: e + 7 N Phosphorus-30 is a positron-emitting radioisotope suitable for use in PET scans. What new element is formed when phosphorus-30 decays? Exercise 4.6 Chapter 4

1 April 2017 04-01 Title: Distribution Chart for Radiation Exposure Caption: Pie chart showing the sources of radiation exposure. Notes: Percent exposure from various radiation sources. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-02 Title: Alpha and Beta Emission Caption:
Nuclei undergoing alpha and beta emission. Notes: Radioactive decay is a balanced reaction in terms of mass numbers and charges. Chapter 4 Chapter 4

1 April 2017 04-03 Title: Positron Emission and Electron Capture Caption: Nuclei undergoing positron emission and electron capture. Notes: Radioactive decay is a balanced reaction in terms of mass numbers and charges. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-04 Title: Tritium Decay Caption:
Graph showing the decay of tritium with a half-life of 12.3 years. Notes: Assume that radioactivity is essentially gone after 10 half-lives. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-08 Title: Analogy for Radiation Penetration
Caption: Alpha particles stop more quickly than beta particles. Gamma radiation is the hardest to stop. Notes: Alpha particles are highly dangerous inside the body. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-09 Title: Penetrating Power of Radiation
Caption: The relative penetrating power of alpha, beta, and gamma radiation. Notes: Like X-rays, gamma rays can pass through the body. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-10 Title: Nuclear Binding Energy for Helium
Caption: The difference in mass between the individual particles in the helium nucleus and its actual mass. The missing mass is converted into the nuclear binding energy. Notes: The missing mass is known as the mass defect. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-11 Title: Nuclear Binding Energy Caption:
Graph showing that nuclear binding energy reaches a maximum at iron. Notes: Note that very low mass elements to the left of iron undergo fusion to gain nuclear stability while those to the right of iron undergo fission. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-12 Title: Nuclear Fission Caption:
The fission of an atom of uranium-235. Notes: The fission of a particular isotope does not always produce the same products. Not all atoms undergo fission. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-13 Title: Nuclear Chain Reaction Caption:
The process by which a chain reaction develops when uranium-235 undergoes fission. Note the different fission products. Notes: Uncontrolled chain reactions lead to powerful explosions. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-17-01UN Title: End-of-Chapter Problem 63
Caption: Fission reaction for end-of-chapter Problem 63. Notes: problem image Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-TB01 Title:
Table 4.1 Common Types of Radiation in Nuclear Reactions Caption: Properties of alpha, beta, and gamma radiation. Notes: the three major types of radiation Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-TB02 Title:
Table 4.2 Radioactive Decay and Nuclear Change Caption: Changes in atomic and mass number during radioactive decay processes. Notes: Atomic and mass numbers are balanced. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-TB03 Title:
Table 4.3 Some Differences Between Chemical Reactions and Nuclear Reactions Caption: Comparison of chemical and nuclear reactions. Notes: Nuclear reactions may produce different daughter elements, while chemical reactions conserve the starting elements. Chapter 4 Chapter 4

Chapter 4 1 April 2017 04-TB04 Title:
Table 4.4 Nuclear Symbols for Subatomic Particles Caption: Symbols used to represent particles in nuclear reaction equations. Notes: balancing nuclear reactions Chapter 4 Chapter 4

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