21Nuclear Chemistry

A nuclear submarine uses energy released by nuclear reactions.

746 S ON CU O F TEKS CHEMYSTERY 12B

An Ice-Age Baby In 2007, a reindeer herder in north-central Russia thought he spotted the frozen remains of a reindeer. What he found was a perfectly preserved baby wooly mammoth about the size of a large dog. The only thing missing was its shaggy coat. Scientists named the mammoth Lyuba, which means “love” in Russian. Wooly mammoths are an extinct species related to modern elephants. These large mammals had curved tusks and long hair. They lived on Earth from about 1.8 million years ago until about 11,500 years ago. How do scientists know when Lyuba lived and died? As you read about radioactive decay, think about how the process can help scientists find the age of a wooly mammoth fossil.

Take a trip back in time with the Untamed Science crew to “meet” the scientist who first used the term radioactivity and to learn more about the radioactive decay process.

Texas Essential Knowledge and Skills

Readiness TEKS: 12B Describe radioactive decay process in terms of balanced nuclear equations. Supporting TEKS: 12A Describe the characteristics of alpha, beta, and gamma radiation. 12C Compare fission and fusion reactions. TEKS: 3D Evaluate the impact of research on scientific thought, society, and the environment. 2I Communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology-based reports. 2H Organize, analyze, evaluate, make inferences, and predict trends from data.

Nuclear Chemistry 747 21.1 Nuclear Radiation In this lesson, you will learn how to describe radioactive decay process in terms of balanced nuclear equations (TEKS 12B). You will also learn about the characteristics of alpha, beta, and gamma radiation (TEKS 12A). Also TEKS 3D. CHEMISTRY & YOU Q: What makes some types of radiation more dangerous than other types? Atoms emit electromagnetic radiation when an electron moves from a higher energy level to a lower energy level. Most electromagnetic radiation, such as visible light, has low energy, low penetrating power, and is not dangerous. X-rays are an exception. Lengthy or frequent exposure to X-rays can damage cells in your body. This lesson will help you understand the basic processes of Key Questions nuclear chemistry and why exposure is also a concern with nuclear radiation. How do nuclear reactions differ from chemical reactions? Radioactive Decay TEKS 12B, 3D What are three types of How do nuclear reactions differ from chemical reactions? nuclear radiation? In 1896, the French chemist Antoine Henri Becquerel made an accidental Vocabulary discovery. He was studying the ability of uranium salts that had been • radioactivity exposed to sunlight to fog photographic film plates. During bad weather, • nuclear radiation when Becquerel could not expose a sample to sunlight, he left the sample on • radioisotope top of the photographic plate. When he developed the plate, he discovered • alpha particle that the uranium salt still fogged the film. Bequerel’s research impacted the • beta particle scientific thought of his associates Marie and Pierre Curie. The Curies were • gamma ray able to show that rays emitted by uranium atoms caused the film to fog. • nuclear equation Marie Curie is shown in Figure 21.1. She used the term radioactivity to refer Figure 21.1 Marie Curie to the spontaneous emission of rays or particles from certain elements, such Marie Curie and her husband as uranium. Radioactivity is also known as radioactive decay. The rays and Pierre shared the 1903 Nobel Prize particles emitted from a radioactive source are called nuclear radiation. in physics with Becquerel for their Radioactive decay is an example of a nuclear reaction. In both chemical pioneering work on radioactivity. reactions and nuclear reactions, atoms become more stable. The word stable means “constant” or “not likely to change.” In a chemical reaction, atoms tend to attain a more stable electron configuration by transferring or sharing electrons. Nuclear reactions begin with unstable isotopes, or radioisotopes. Atoms of these isotopes become more stable when changes occur in their nuclei. The changes are always accompanied by the emission of large amounts of energy. Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure, or the presence of catalysts. Also, nuclear reactions of a given radioisotope cannot be slowed down, sped up, or stopped. Radioactive decay is a spontaneous process that does not require an input of energy. If the product of a nuclear reaction is unstable, it will decay too. The process continues until unstable isotopes of one element are changed, or transformed, into stable isotopes of a different element. These stable isotopes are not radioactive.

748 Table 21.1 Characteristics of Alpha, Beta, and Gamma Radiation

Type Consists of Symbol Charge Mass (amu) Common source Penetrating power Low Alpha particles Alpha radiation α, 4 2+ 4 Radium-226 (0.05 mm body (helium nuclei) 2He tissue) Beta particles Moderate (4 mm Beta radiation β, 0 1− 1/1837 Carbon-14 (electrons) −1e body tissue) High-energy Very high Gamma radiation electromagnetic γ 0 0 Cobalt-60 (penetrates body radiation easily)

Types of Radiation TEKS 12A, 12B What are three types of nuclear radiation?

Radiation is emitted during radioactive decay. Three types of nuclear ELPS 4.F.3 radiation are alpha radiation, beta radiation, and gamma radiation. With a partner, use the diagrams Table 21.1 describes the characteristics of alpha, beta, and gamma radiation. on pages 750 and 751 to explain some key differences among the Alpha Radiation Some radioactive sources emit helium nuclei, which are different types of radiation. As you also called alpha particles. Each alpha particle contains two protons and differentiate, keep in mind the order two neutrons and has a double positive charge. An alpha particle is of the three symbols alpha, beta, 4 and gamma as the first, second, and written 2He or α. third letters of the Greek alphabet. The radioisotope uranium-238 emits alpha radiation and is transformed into another radioisotope, thorium-234. When an atom loses an alpha particle, the atomic number of the product is lower by two and its mass number is lower by four. Figure 21.2 illustrates this process.

238 Radioactive 234 4 92U decay 90Th + 2He (α emission) Uranium-238 Thorium-234 Alpha particle

Alpha particle Figure 21.2 Alpha Decay 4He Uranium-238 decays and forms 2 thorium-234. The radiation emitted is an alpha particle. Interpret Diagrams 234 Th Describe the structure of 90 an alpha particle. 238 92U

A nuclear equation is a representation of a nuclear reaction; the symbols of the reactants are connected by an arrow with the symbols of the products. You can describe radioactive decay processes in terms of balanced nuclear equations. In a balanced nuclear equation, the sum of the mass numbers (superscripts) on the right equals the sum on the left. The same is true for the atomic numbers (subscripts). Because of their large mass and charge, alpha particles do not travel very far and are not very penetrating. The surface of your skin can stop them.

Nuclear Chemistry 749 Beta Radiation An electron resulting from the breaking apart of a neutron in an atom is called a beta particle. The neutron breaks apart into a proton, which remains in the nucleus, and a fast-moving Beta particle 0 electron, which is released. –1 e 1 1 0 0n 1p + −1e Neutron Proton Electron 14 6 C (beta particle)

The symbol for the electron has a subscript of −1 and a superscript 14 N 7 of 0. The −1 represents the charge on the electron. The 0 represents the extremely small mass of the electron compared to the mass of Figure 21.3 Beta Decay a proton. When a carbon-14 atom Carbon-14 is a radioisotope. It emits a beta particle as it decays decays, the products are and forms nitrogen-14. Figure 21.3 illustrates this reaction. nitrogen-14 and a beta particle. 14 14 0 6C 7N + −1e (β emission) Carbon-14 Nitrogen-14 Beta particle (radioactive) (stable)

The nitrogen-14 atom has the same mass number as carbon-14, but its atomic number has increased by 1. It contains an additional proton and one fewer neutron. The nuclear equation is balanced. A beta particle has less charge than an alpha particle and much less mass than an alpha particle. Thus, beta particles are more penetrating than alpha particles. Beta particles can pass through paper but are stopped by aluminum foil or thin pieces of wood. Because of their opposite charges, alpha and beta radiation can be separated by an electric field, as shown in Figure 21.4.

Lead block Aligning slot Alpha particles (positive charge) –

Gamma rays (no charge) + Electric ﬁeld Radioactive source Beta particles Detecting screen (negative charge)

Figure 21.4 The Effect of an Electric Field on Radiation An electric field has a different effect on each type of radiation. Alpha and beta particles move in opposite directions. Alpha particles move toward the negative plate and beta particles move toward the positive plate. Gamma rays are not deflected as they pass between the plates. Apply Concepts Why are gamma rays not deflected?

750 Chapter 21 • Lesson 1 Figure 21.5 Relative Penetrating Lead block Paper Wood Lead Power of Nuclear Radiation Because of their large mass and charge, alpha particles (red) are the least penetrating of the three main types of nuclear radiation. Gamma rays (yellow) have no mass or charge Some and are the most penetrating. gamma Compare How penetrating are rays beta particles (green) compared to Radioactive source alpha particles and gamma rays?

Gamma Radiation A high-energy photon emitted by a radioisotope is called a gamma ray. The high-energy photons are a form of electromagnetic radiation. Nuclei often emit gamma rays along with alpha or beta particles during radioactive decay. The following examples illustrate two radioactive decay processes in terms of balanced nuclear equations.

230 226 4 90Th 88Ra + 2He + γ Thorium-230 Radium-226 Alpha Gamma particle ray

234 234 0 90Th 91Pa + −1e + γ Thorium-234 Protactinium-234 Beta Gamma particle ray

Gamma rays have no mass and no electrical charge. So the emission CHEMISTRY & YOU of gamma radiation does not alter the atomic number or mass number of Q: Gamma rays can be dangerous an atom. Because gamma rays are extremely penetrating, they can be very because of their penetrating power. dangerous. For example, gamma rays pass easily through paper, wood, and What property determines the rela- the human body. They can be stopped, although not completely, by several tive penetrating power of electro- meters of concrete or several centimeters of lead, as shown in Figure 21.5. magnetic radiation?

21.1 LessonCheck TEKS 12A, 12B

1. Compare What factors do not affect 5. Describe In your own words, describe radioactive nuclear reactions, but do affect chemical decay processes in terms of balanced nuclear equations. reactions? Identify the two items that must be equal in a balanced nuclear reaction. 2. Describe Briefly describe the characteristics of alpha, beta, and gamma 6. Relate Cause and Effect How does alpha decay affect radiation. the mass number of a nucleus? How does beta decay affect the mass number? 3. Identify What part of an atom undergoes change during radioactive decay? 7. Identify Which of the three types of radiation described in this lesson is the most penetrating, and why? 4. Compare and Contrast How is the atomic number of a nucleus changed by alpha decay? 8. Predict When polonium-210 decays by alpha radiation, By beta decay? By gamma decay? what isotope is formed?

Nuclear Chemistry 751 21.2 Nuclear Transformations In this lesson, you will learn how to describe radioactive decay processes in terms of balanced nuclear equations (TEKS 12B), how to organize, analyze, and predict trends from data (TEKS 2H), and how to communicate valid conclusions supported by data through methods such as graphs and summaries (TEKS 2I). Also TEKS 12A. CHEMISTRY & YOU Q: What is the source of radon in homes? All the isotopes of radon gas are unstable and emit radiation. Inhaled radon is the second leading cause of lung cancer in the United States. Radon may accumulate in a basement that is not well ventilated. Because radon is a colorless, odorless gas, people often do not know that they are being exposed to high levels of radon. Test kits are available to measure the levels of radon in a building. In this lesson, you will study the decay series that produces this hazardous gas. Key Questions What determines the type of Nuclear Stability and Decay TEKS 12B, 12A decay a radioisotope undergoes? What determines the type of decay a radioisotope undergoes? How much of a radioactive All atomic nuclei, except those of hydrogen atoms, consist of neutrons sample remains after each half- and two or more protons. If a force did not hold these subatomic particles life? together, the like-charged protons would repel one another and fly apart. What are two ways in which The nuclear force is an attractive force that acts between all nuclear particles transmutation can occur? that are extremely close together, such as protons and neutrons in a nucleus. At these short distances, the nuclear force dominates over electromagnetic Vocabulary repulsions and holds the nucleus together. • nuclear force More than 1,500 different nuclei are known. Only 264 of the known • band of stability nuclei are stable and do not decay. The rest are unstable and will change over • positron time. The stability of a nucleus depends on the ratio of neutrons to protons. • half-life Figure 21.6 shows a graph of the number of neutrons vs. the number of pro- • transmutation • transuranium elements tons for all known stable nuclei. The region of the graph in which these points are located is called the band of stability. For elements of low atomic number (below about 20), this ratio is about 1. Above atomic number 20, stable nuclei have more neutrons than protons. A nucleus may be unstable and undergo spontaneous decay for different reasons. The neutron-to-proton ratio in a radioisotope determines the type of decay that occurs. Some nuclei are unstable because they have too many neutrons relative to the number of protons. When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus. A neutron that emits an electron becomes a proton. 1 1 0 0n 1p + −1e This process is known as beta emission. It increases the number of protons while decreasing the number of neutrons. Radioisotopes that undergo beta emission include the following. 66 66 0 29Cu 30Zn + −1e

14 14 0 6C 7N + −1e

752 Interpret G r a p h s TEKS 2H

Figure 21.6 A plot of neutrons vs. protons for all stable nuclei forms a pattern called the band of Ratio of Neutrons to Number of stability, which is shown in purple. The green line Protons for Stable Nuclei shows what the pattern would be if the ratio were 1 for every nucleus. 140 Ratio≈1.5 a. Identify What does each dot represent? 120 Band of b. Analyze Data What is the ratio of neutrons stability 100 to protons for tin (Sn, atomic number = 50)? Ratio≈1.3 c. Predict Trends How does the neutron- 80 to-proton ratio change as the number of protons 60 Ratio≈1.2 increases in stable nuclei? n0 = 1 40 p + 1

Number of neutrons (Ratio = 1.0) 20

0 20 40 60 80 100 120 Number of protons

Other nuclei are unstable because they have too few neutrons relative to the number of protons. These nuclei increase their stability by converting a proton to a neutron. An electron is captured by a nucleus during this process, which is called electron capture. Here are two examples of electron capture. 59 0 59 28Ni + −1e 27Co

37 0 37 18Ar + −1e 17Cl A positron is a particle with the mass of an electron but a positive charge. 0 Its symbol is +1e. During positron emission, a proton changes to a neutron, just as in electron capture. Here are two examples of positron emission. 8 8 0 5B 4Be + +1e

15 15 0 8O 7N + +1e When a proton is converted to a neutron, the atomic number decreases by 1 and the number of neutrons increases by 1. All nuclei that have an atomic number greater than 83 are radioactive. These nuclei have both too many neutrons and too many protons to be stable. Therefore, they undergo radioactive decay. Most of them emit alpha particles. Alpha emission increases the neutron-to-proton ratio, which tends to increase the stability of the nucleus. In alpha emission the mass number decreases by four and the atomic number decreases by two. 226 222 4 88Ra 86Rn + 2He

232 228 4 90Th 88Ra + 2He Recall that conservation of mass is an important property of chemical reactions. In contrast, mass is not conserved during nuclear reactions. An extremely small quantity of mass is converted into the energy released during radioactive decay.

Nuclear Chemistry 753 Sample P r o b l e m 21.1 TEKS 12B

Balancing a Nuclear Equation 40 40 Write a balanced nuclear equation for the radioactive decay of 19K to 20Ca.

➊ Analyze Identify the relevant concepts. Apply the rules for balancing nuclear equations. The sum of the mass numbers (superscripts) on the right must equal the sum on the left. The same is true for the atomic numbers (subscripts).

➋ Solve Apply the concepts to this problem.

Write a skeleton equation. Include This is a radioactive decay process, 40 40 a question mark for the radioactive 19K 20Ca + ? so the radioactive particle appears particle. on the right side of the equation.

The mass numbers (40) are balanced, but the atomic numbers (19 and 20) are not. Balance the equation by determining A beta particle has almost no mass and a the identity of the particle. charge of 1–. So adding a beta particle to the right side will balance the equation.

40 40 0 19K 20Ca + -1e

9. Write a balanced nuclear equation for the 10. Write a balanced nuclear equation for alpha 60 60 252 radioactive decay of 26 Fe to 27 Co. emission by 99 Es.

Half-Life How much of a radioactive sample remains after each half-life? CHEMISTRY & YOU Every radioisotope has a characteristic rate of decay, which is measured by its half-life. A half-life (t1) is the time required for one-half of the Q: Uranium compounds are 2 found in rocks and in soils that nuclei in a radioisotope sample to decay to products. During each form from these rocks. How can half-life, half of the remaining radioactive atoms decay into atoms of a these uranium compounds lead new element. to a build up of radon in homes Comparing Half-Lives Half-lives can be as short as a second or as long and other buildings? as billions of years. Scientists analyze radioisotopes with long half-lives to determine the age of ancient objects. Many artificially produced radioisotopes have short half-lives, which makes them useful in nuclear medicine. Short-lived isotopes are not a long-term radiation hazard for patients.

754 Chapter 21 • Lesson 2 238 234 234 234 92U 90Th 91Pa 92 U Figure 21.7 Decay Series of U-238 4.5  109 yr 25 days 6.7 h Uranium-238 decays through a series of radioactive intermediates, including radon (Rn) gas. 222 226 230 86Rn 88Ra 90Th Interpret Diagrams What is the 2.3  103 yr 8  104 yr 2.5  105 yr stable end product of this series?

218 214 214 84Po 82Pb 83Bi 4 days 3 min 27 min

210 210 214 83Bi 82Pb 84Po 22 yr 1.6 104 s 20 minutes

210 206 84Po 82Pb Stable isotope 5 days 138 days

One isotope that has a long half-life is uranium-238. It decays through a complex series of unstable isotopes to the stable isotope lead-206. Figure 21.7 summarizes this process. The age of uranium-containing minerals can be estimated by measuring the ratio of uranium-238 to lead-206. Because the half-life of uranium-238 is 4.5 × 109 years, it is possible to use its half-life to date rocks as old as the solar system. Radiocarbon Dating Scientists often find the age of an object that was 14 once part of a living system by measuring the amount of carbon-14 ( 6C) it contains. Carbon-14 has a half-life of 5730 years. Most of Earth’s carbon, 12 13 14 however, consists of the more stable isotopes 6C and 6C. The ratio of 6C to the other carbon isotopes in the environment is fairly constant because high- 14 energy cosmic rays from space constantly produce 6C in carbon dioxide in the upper atmosphere. Plants use carbon dioxide to produce carbon compounds, such as glu- cose. In those compounds, the ratio of carbon isotopes is the same as in the air. The same ratio is maintained as animals consume the plants, and other animals. Thus, the ratio of carbon-14 to other carbon isotopes is constant during an organism’s lifetime. When an organism dies, it stops exchanging 14 carbon with the environment and its radioactive 6C atoms decay without 14 being replaced. Therefore, the ratio of 6C to stable carbon in the remains of an organism changes in a predictable way. Archaeologists can use this data to estimate when an organism died. Table 21.2 Exponential Decay Function You can use the following equation to calcu- Decay of Initial Amount late how much of an isotope will remain after a given number of half-lives. (A 0) of Radioisotope Half- 1 n Amount Remaining A ∙ A0 ∙ ( 2 ) Life

1 0 0 A 0 × (2) = A 0 In the formula, A stands for the amount remaining, A0 for the initial amount, 1 1 1 and n for the number of half-lives. The exponent n indicates how many times 1 A0 × (2) = A 0 × 2 1 A0 must be multiplied by 2 to determine A. Table 21.2 shows examples in 2 A × (1)2 = A × 1 × 1 which n = 1 and n = 2. 0 2 0 2 2

Nuclear Chemistry 755 Sample P r o b l e m 21.2

Using Half-lives in Calculations

Carbon-14 emits beta radiation and decays with a half-life (t1) of 5730 years. 2 Assume you start with a mass of 2.00 × 10−12 g of carbon-14. a. How long is three half-lives? b. How many grams of the isotope remain at the end of three half-lives?

➊ Analyze List the knowns and the unknowns. To calculate the length of three half-lives, multiply the KNOWNS UNKNOWNS 1 ∙ ∙ half-life by three. To find the mass of the radioisotope t2 5730 years 3 half-lives ? years 1 –12 initial mass(A0) 2.00 ∙ 10 g remaining, multiply the original mass by 2 for each mass remaining ∙ ? g half-life that has elapsed. number of half-lives (n) ∙ 3

➋ Calculate Solve for the unknowns.

Multiply the half-life of carbon-14 by a. t 1 ∙ n ∙ 5730 years ∙ 3 ∙ 17,190 years the total number of half-lives. 2

The initial mass of carbon-14 is reduced 1 1 1 by one half for each half-life. So b. Remaining mass ∙ 2.00 ∙ 10−12 g ∙ ∙ ∙ 1 2 2 2 multiply by 2 three times. ∙ 0.250 ∙ 10−12 g

∙ 2.50 ∙ 10−13 g

You can get the same answer by using n 3 1 −12 1 the equation for an exponential decay c. A ∙ A0 (2) ∙ (2.00 ∙ 10 g) (2) function. −12 1 ∙ (2.00 ∙ 10 g) (8) ∙ 0.250 ∙ 10−12 g

∙ 2.50 ∙ 10−13 g

➌ Evaluate Do the results make sense? The mass of carbon-14 after three half-lives should be one-eighth of the original mass. If you divide 2.50 × 10−13 g by 2.00 × 10−12 g, 1 you will get 12.5%, or 8 . For Problem 11, first figure out the number of half-lives.

11. Manganese-56 is a beta emitter with 12. Thorium-234 has a half-life of 24.1 days. a half-life of 2.6 h. What is the mass of Will all the thorium atoms in a sample manganese-56 in a 1.0-mg sample of the decay in 48.2 days? Explain. isotope at the end of 10.4 h?

756 Chapter 21 • Lesson 2 Transmutation Reactions TEKS 12B What are two ways in which transmutation can occur? For thousands of years, alchemists tried to change lead into gold, an element which is more highly valued than lead. Despite much effort, they were not able to achieve their goal. What they wanted to achieve is transmutation, or the conversion of an atom of one element into an atom of another element. This change can occur in at least two ways. Transmutation can occur by radioactive decay or when particles bombard the nucleus of an atom. The particles may be protons, neutrons, alpha particles, or small atoms. Transmutations are common in nature. The production of carbon-14 from nitrogen-14 that takes place in the upper atmosphere is one example. Recall the decay series of uranium-238, which was described in Figure 21.7. In this series, 14 transmutations occur before a stable isotope of lead is produced. Some transmutations that do not occur in nature can be forced to occur in a laboratory or in a nuclear reactor. Ernest Rutherford performed the earliest artificial transmutation in 1919. He bombarded nitrogen gas with alpha particles. The results of this action are shown in Figure 21.8. As the nitrogen atoms absorb the alpha particles, they form fluorine-18 atoms.

14 4 18 7N + 2He 9F Nitrogen-14 Alpha Fluorine-18 particle The unstable fluorine atoms quickly decay to form a stable isotope of oxygen and a proton.

18 17 1 9F 8O + 1p Fluorine-18 Oxygen-17 Proton

1 p Figure 21.8 The Transmutation 1 of Nitrogen-14 Proton The first artificial transmutation reaction involved bombarding + nitrogen gas with alpha particles. Interpret Diagrams Which

4 14 18 17 particle is the intermediate in 2 He 7 N 9 F 8 O this nuclear reaction? Alpha Nitrogen Unstable Oxygen particle atom ﬂuorine atom

Rutherford’s experiment eventually led to the discovery of the proton. When he and other scientists analyzed their data, they noticed a pattern as they did different transmutation experiments. In every case, hydrogen nuclei (protons) were emitted. Scientists realized that these hydrogen nuclei must have a fun- damental role in atomic structure. James Chadwick’s discovery of the neutron in 1932 also involved a transmutation experiment. Neutrons were produced when beryllium-9 was bombarded with alpha particles.

9 4 12 1 4Be + 2He 6C + 0n Beryllium-9 Alpha Carbon-12 Neutron particle

Nuclear Chemistry 757 Elements with atomic numbers above 92, the atomic number of uranium, are called transuranium elements. All of these elements are radioactive. All transuranium elements undergo transmutation. These elements are synthesized in nuclear reactors and nuclear accelerators. Reactors produce beams of low- energy particles. Accelerators are used to increase the speed of bombarding particles to very high speeds. Sometimes particles must pass through a series of accelerators before they reach the desired speed. The European Organization for Nuclear Research, known as CERN, has a number of accelerators at its site on the border between France and Switzerland. Figure 21.9 shows CERN’s largest accelerator. When uranium-238 is bombarded with the relatively slow neutrons from a nuclear reactor, some uranium nuclei capture these neutrons. The product is uranium-239. 238 1 239 92U + 0n 92 U Uranium-239 is radioactive and emits a beta particle. The other product is an isotope of the artificial radioactive element neptunium (atomic number 93). 239 239 0 92 U 93 Np + −1 e Neptunium is unstable and decays, emitting a beta particle and a second artificial element, plutonium (atomic number 94). 239 239 0 93 Np 94 Pu +−1 e Figure 21.9 Particle Accelerator Plutonium and neptunium are both transuranium elements. The The Large Hadron Collider is the most powerful majority of these elements do not occur in nature. Scientists in accelerator in the world. It has a circumference of about 27 kilometers and is about 100 meters Berkeley, California, synthesized the first two artificial elements underground. The photograph shows a very small in 1940. Since that time, more than 25 additional transuranium part of the collider. elements have been produced artificially.

21.2 LessonCheck TEKS 12B 13. Identify What factor determines the 17. Write Balanced Nuclear Equations Complete the type of decay that occurs in a radioisotope? following nuclear equations. Use what you know about balanced nuclear equations to identify the missing 14. Predict How much of a sample of particles. radioisotope remains after one half-life? 27 4 30 27 0 a. 13 Al + 2 He 14 Si + ? c. 14 Si −1 e + ? After two half-lives? 214 4 66 66 b. 83 Bi 2 He + ? d. 29 Cu 30 Zn + ? 15. Explain How can transmutation 18. Calculate A radioisotope has a half-life of 4 days. How occur in a stable isotope? much of a 20-gram sample of this radioisotope remains 16. Predict Which nuclei would you predict at the end of each time period? to be stable? Explain your answer. a. 4 days b. 8 days a. 9 3 Li 19. Calculate 59 The mass of cobalt-60 in a sample decreased b. 27 Co from 0.800 g to 0.200 g over a period of 10.5 years. 20 c. 8 O From this information, calculate the half-life of 146 d. 60 Nd cobalt-60.

758 Chapter 21 • Lesson 2 Small-Scale Lab TEKS 12B, 2I, 2H

Radioactivity and Half-Lives

Purpose To simulate the transformation of a radioactive isotope over time, graph the data, and relate the data to radioactive decay and half-lives

Materials • coin • graph paper

Procedure Analyze and Conclude 1. On a sheet of paper, organize your data into a 1. Graph data table similar to the one below. Use graph paper to plot the number of flips (y-axis) versus the trial number (x-axis). Draw 2. For trial 1, flip a coin 100 times. In your table, a smooth line to connect the points. record the total number of heads that result. 2. Analyze Data Is the rate of the number of 3. For trial 2, flip the coin the same number of times heads produced over time linear or nonlinear? Is the as the number of heads in trial 1. Record the number rate constant over time or does it change? of flips and the number of heads that result. 3. Relate Cause and Effect Why does each trial 4. Continue the procedure until you obtain no reduce the number of heads by about one-half? more heads. 4. Use Models A half-life is the time required for one-half of the atoms of a radioisotope to decay to Number Number products. What value represents one half-life for the Trial of ﬂips of heads process of flipping coins?

1 100 You’re the Chemist 1. Communicate Valid Conclusions Design and 2 carry out an experiment using a single die to model radioactive decay. Communicate your valid conclu- 3 sion by plotting a graph of your data and writing a 4 short summary that explains how the data support your conclusion. 5 2. Write Balanced Nuclear Equations Radon-222 undergoes alpha decay to produce polonium-218. 6 Write a balanced nuclear equation to describe this process. 7 3. Calculate The half-life of radon-222 is 3.8 days. Determine how long it takes for only one eighth of a 8 sample of radon-222 to remain.

Small-Scale Lab 759 21.3 Fission and Fusion

In this lesson, you will compare fission and fusion reactions (TEKS 12C).

CHEMISTRY & YOU Q: Where does the sun’s energy come from? The sun appears as a bright, fiery ball in the sky. The sun is so bright that you should never look at it directly without eye protection. The sun is about halfway through its life cycle. It has been producing energy for about 5 billion years and is expected to continue to produce energy for about 5 billion more. In this lesson, you will study the nuclear reaction that takes place in the sun.

Nuclear Fission TEKS 12C Key Questions What happens in a nuclear chain reaction? What happens in a nuclear When the nuclei of certain isotopes are bombarded with neutrons, the nuclei chain reaction? split into smaller fragments. This process is called fission. Uranium-235 and plutonium-239, for example, are fissionable isotopes. Figure 21.10 shows how How do fission reactions uranium-235 breaks into two smaller fragments when struck by a slow-moving and fusion reactions compare? neutron. At the same time, more neutrons are released by the fission. These Vocabulary neutrons strike the nuclei of other uranium-235 atoms, which causes a chain • fission reaction. In a chain reaction, some of the emitted neutrons react with • neutron moderation other fissionable atoms, which emit neutrons that react with still more • neutron absorption fissionable atoms. • fusion Nuclear fission can release enormous amounts of energy. The fission of 1 kg of uranium-235, for example, yields an amount of energy equal to that produced when 20,000 tons of dynamite explode. In an uncontrolled nuclear chain reaction, all the energy is released in fractions of a second. An atomic bomb is a device that can trigger an uncontrolled nuclear chain reaction.

Neutron 91 Figure 21.10 Fission of Uranium 36 Kr When struck by a slow-moving Krypton-91 neutron, a uranium-235 nucleus breaks into two smaller nuclei and releases three neutrons. 1 n Energy 3 0 Predict What happens when the released neutrons strike other uranium-235 nuclei? 235 U 236 U 92 92 142 Uranium-235 Uranium-236 56 Ba (ﬁssionable) (very unstable) Barium-142

760 Fission can be controlled so energy is released more slowly. ELPS 3.C.4 Nuclear reactors, such as the one shown in Figure 21.11, use con- With a partner, use the captions trolled fission to produce useful energy. The reaction takes place and labels to discuss what is pic- within uranium-235 or plutonium-239 fuel rods. Much of the tured in Figures 21.10 and 21.13, energy produced in this reaction is in the form of heat. A fluid, usu- the diagrams of fission and fusion. ally liquid sodium or water, removes heat from the core, or central Then take turns giving each other a guided talk-through of what happens part, of the reactor. Thus, the fluid is called a coolant. The heated in these processes. Use connecting fluid is used to change water to steam, which drives a turbine that words in your talk. For example: generates electricity. The control of fission in a nuclear reactor and, since, because, before, after, involves two steps, neutron moderation and neutron absorption. then, and so. Neutron Moderation Neutron moderation is a process that slows down neutrons so the reactor fuel can capture them to continue the chain reaction. Moderation is necessary because most of the neutrons produced move so fast that they would pass right through a nucleus without being captured. Water and carbon in the form of graphite are good moderators. Figure 21.11 Nuclear Reactor A nuclear reactor is used to produce Neutron Absorption To prevent the chain reaction from going electricity. A coolant absorbs heat too fast, some of the slowed neutrons must be trapped before produced by the controlled fission they hit fissionable atoms. Neutron absorption is a process that reaction and transfers the heat to decreases the number of slow-moving neutrons. Control rods, water, which changes to steam. The steam drives a turbine, which drives a made of materials such as cadmium, are used to absorb neutrons. generator that produces electricity. When the control rods extend almost all the way into the reactor Interpret Diagrams What core, they absorb many neutrons, and fission occurs slowly. As the happens to the steam after it rods are pulled out, they absorb fewer neutrons and the fission pro- drives the turbine? cess speeds up. If the chain reaction were to go too fast, heat might be produced faster than the coolant could remove it. The reactor core would overheat, which could lead to mechanical failure and release of radioactive materials into the atmosphere. Ultimately, a meltdown of the reactor core might occur.

Containment Shell

Steam Electrical Heated output Reactor Generator coolant Steam Steam Control Water rod Condenser

Fuel 38ºC water rod Carbon moderator 27ºC water

Coolant Pump Pump Pump

Nuclear Chemistry 761 Nuclear Waste Fuel rods from nuclear power plants are one major source of nuclear waste. The fuel rods are made from a fissionable isotope, either READING SUPPORT uranium-235 or plutonium-239. The rods are long and narrow—typically Build Reading Skills: 3 meters long with a 0.5-cm diameter. In a typical reactor, three hundred fuel Inference When you make an rods are bundled together to form an assembly, and one hundred assemblies inference, you are really reading are arranged to form the reactor core. During fission, the amount of fission- between the lines. An inference should be based on information able isotope in each fuel rod decreases. Eventually the rods no longer have in the text and any background enough fuel to ensure that the output of the power station remains constant. knowledge you may have. After The isotope-depleted, or spent, fuel rods must be removed and replaced with you read the Nuclear Waste new fuel rods. section, use inference to explain Spent fuel rods are classified as high-level nuclear waste. They contain a how the storage of nuclear wastes mixture of highly radioactive isotopes, including fission products and what could affect the environment. remains of the nuclear fuel. Some of these fission products have very short half-lives, on the order of fractions of seconds. Others have half-lives of hun- dreds or thousands of years. All nuclear power plants have holding tanks, or “swimming pools,” for spent fuel rods. Water cools the spent rods, and also acts as a radiation shield to reduce the radiation levels. The pools, like the one shown in Figure 21.12, are typically 12 meters deep. Storage racks at the bottom of these pools are designed to hold the spent fuel assemblies. The rods continue to produce heat for years after their removal from the core. The spent fuel rods may spend a decade or more in a holding tank. In the past, plant operators expected spent fuel rods to be reprocessed. Any left- over fissionable isotope in the rods would be recycled in the manufacture of new fuel rods. However, with large deposits of uranium ore available—many in the United States—it is less expensive to mine new fuel than to reprocess depleted fuel. At some nuclear plants, the storage pool has no space left. In order to keep these plants open, their fuel rods must be moved to off-site storage facilities. Finding appropriate storage sites is difficult because high-level waste may need be stored for a long time. Plutonium-239, for example, will not decay to safe levels for 240,000 years. Often, people are concerned about having nuclear waste stored nearby or shipped through their communities.

Figure 21.12 Storage of Fuel Rods Racks at the bottom of this pool contain spent fuel rods.

762 Chapter 21 • Lesson 3 Figure 21.13 Fusion in the Sun In the sun, hydrogen nuclei fuse to + + Energy produce helium nuclei. Interpret Diagrams What are the other products of this 1 4 0 reaction? 4 1 H 2 He 2+1 e Hydrogen nuclei Helium nucleus Positrons

Nuclear Fusion TEKS 12C How do fission reactions and fusion reactions compare? The sun, directly and indirectly, is the source of most energy used on Earth. The energy emitted by the sun results from nuclear fusion. Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei. Figure 21.13 shows that the reaction also produces two positrons. When comparing fission and fusion reactions, fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split apart and form smaller nuclei. However, fusion reactions occur only at very high temperatures—in excess of 40,000,000°C. The use of controlled nuclear fusion as an energy source on Earth is appealing. The potential fuels are inexpensive and readily available. Some scientists are studying a reaction in which a deuterium (hydrogen-2) nucleus and a tritium (hydrogen-3) nucleus combine to form a helium nucleus. CHEMISTRY YOU 2 3 4 1 & 1H + 1H 2He + 0n + energy Q: The high temperatures The problems with fusion lie in achieving the high temperatures needed needed to support fusion exist to start the reaction and in containing the reaction once it has started. The within the sun’s core. Late in high temperatures required to start fusion reactions have been achieved by the sun’s life cycle, other fusion using a fission bomb. Such a bomb is the triggering device used for setting off reactions will occur. What a hydrogen bomb, which is an uncontrolled-fusion device. This process is of element would form when two no use, however, as a controlled generator of power. helium nuclei fuse?

21.3 LessonCheck TEKS 12C 20. Relate Cause and Effect Explain what 25. Interpret Diagrams Review the diagram of a reactor happens in a nuclear chain reaction. in Figure 21.11. What roles does water play in a typical nuclear reactor? 21. Compare In your own words, compare fission and fusion reactions. 26. Infer Some nuclear waste is stored about 600 meters below the desert in New Mexico inside caverns dug 22. Explain What is neutron moderation, and out of an ancient bed of rock salt. The land above the why is it necessary in a nuclear reactor? storage site is owned by the federal government. Why 23. Identify What are two sources of the radio- do you think this location was chosen? active nuclei present in spent fuel rods? 2 7. Describe Read about heavy water reactors on 24. Evaluate Suppose the technical problems page R35 of the Elements Handbook. What is the with fusion reactors could be overcome. advantage of using heavy water instead of ordinary What are some advantages to using a fusion water as a neutron moderator? reactor to produce electricity?

Nuclear Chemistry 763 21.4 Radiation in Your Life

In this lesson, you will learn about the impact of research on the environment and society (TEKS 3D). Also TEKS 2I.

CHEMISTRY & YOU Q: How does a smoke detector work? Smoke detectors can limit injuries or deaths due to fires. A typical household smoke detector contains a small 241 amount of americium, 95Am, in the form of AmO2. Americium-241 is a radioisotope. When the air is smoke-free, a current flows through the smoke detector. When smoke is present, there is a drop in current. This drop is detected by an electronic circuit, which causes an alarm to sound. This lesson will help you understand the role of radiation in smoke detection.

Detecting Radiation TEKS 3D What are three devices used to detect radiation? Key Questions Radiation emitted by radioisotopes has enough energy to knock electrons What are three devices off some atoms of a bombarded substance, producing ions. Thus, the radia- used to detect radiation? tion emitted by radioisotopes is called ionizing radiation. It is not possible for What are some practical humans to see, hear, smell, or feel ionizing radiation. The impact of research uses of radioisotopes? on society and the environment can be seen in the use of detection devices to alert people to radiation around them and to monitor the level of that radia- Vocabulary tion. These devices work because of the effects of the radiation when it strikes • ionizing radiation atoms or molecules in the detector. For example, the radiation can expose a photographic plate, which produces an image such as the one shown in Figure 21.14. When the plate is developed, its darkened areas show where the plate has been exposed to radiation. Some devices rely on the current produced when atoms are ionized. Geiger counters, scintillation counters, and film badges are commonly used to detect radiation.

CHEMISTRY & YOU Q: Radiation emitted in a smoke detector ionizes the nitrogen and oxygen in air, and a current flows. When smoke particles attach to the ions, the ions lose their charge. What happens next?

Figure 21.14 X-Rays X-rays allow doctors to see inside the body without having to cut into the body. Color was added to highlight parts of the image.

764 Geiger Counter A Geiger counter uses a gas-filled metal tube to detect radiation. The tube has a central wire electrode that is connected to a power supply. When ionizing radiation penetrates a thin window at one end of the tube, the gas inside the tube becomes ionized. Because of the ions and free electrons produced, the gas is able to conduct electricity. Each time a Geiger tube is exposed to radiation, current flows. The bursts of current drive electronic counters or cause audible clicks from a built-in speaker. Geiger counters can detect alpha, beta, and gamma radiation. The first small, hand-held Geiger counters were developed in the 1930s. Astronomers use Geiger counters to detect cosmic rays from outer space. Geologists use Geiger counters to search for radioactive minerals, such as uranium ores. These devices are also used to check for leaks in hospitals and other places that use radiation. Figure 21.15 shows one use for a Geiger counter.

Scintillation Counter A scintillation counter uses a phosphor-coated surface to detect radiation. A phosphor is a luminescent material. When ionizing radiation strikes the surface, the phosphor produces bright flashes of light, or scintillations. The number of flashes, and their energies, are detected electronically. The data is then converted into electronic pulses, which are measured and recorded. Scintillation counters are more sensitive than Geiger counters. This means that they can detect some radiation that would not be detected by a Geiger counter. Scintillation counters are used to track the path of radioisotopes Figure 21.15 Geiger Counters through the body. They are also used to monitor the possible transport of This person is using a Geiger counter radioactive materials across national borders and through airports. to check for pockets of radiation in contaminated dirt at a spill site. Film Badge Figure 21.16 is a diagram of a typical film badge. The badge contains layers of photographic film covered with black light- proof paper. The film is sealed in a plastic or metal holder. To reach the film, radiation must pass through a filter, which absorbs some radiation, or a transparent area through which radiation can pass easily. People who work with or near ionizing radiation must wear a film badge to monitor their exposure while they are at work. At specific intervals, the film is removed and developed. The strength and type of radiation exposure are determined by comparing the darkness of the film in all the exposed areas. Records are kept of the results. Film badges do not protect a person from radiation, but they do monitor the degree of exposure. To protect themselves, workers must keep a safe distance from the source of the radiation and use adequate shielding.

Plastic case Filters

Figure 21.16 Film Badge In a film badge, radiation passes through one of Film several filters or through a transparent area before it strikes the film. Different amounts of radiation pass through each area.

Nuclear Chemistry 765 Quick Lab TEKS 2I

Purpose To demonstrate the Inverse-Square Relationships relationship between radiation intensity and the distance from Flashlight Procedure 1cm × 1cm the radiation source 1. Estimate and record the distance square opening Materials (A) from the bulb filament to the front surface of the flashlight. • flashlight 2. Cover the end of a flashlight with • strips of duct tape strips of duct tape. Leave a 1 cm × 1 cm Duct tape • scissors square slit in the center of the tape. • poster board, white 3. Place the flashlight on its side on (50 cm × 50 cm) position, record the distance (B) from a flat surface. Turn on the flashlight. the flashlight to the board and the • meter ruler or tape measure Darken the room. length (L) of one side of the square • flat surface, long enough to 4. Mount a large piece of white poster image on the board. hold the meter ruler board in front of the flashlight, per- 6. On a sheet of graph paper, plot • graph paper pendicular to the horizontal surface. L on the y-axis versus A + B on the 5. Move the flashlight away from the x-axis. On another sheet, plot L2 on board in short increments. At each the y-axis versus A + B on the x-axis.

Analyze and Conclude 1. Communicate Valid Conclusions As the flashlight is moved away from the board, what happens to the intensity of the light in the square image? Use your graphs to describe the relationship between intensity and distance. 2. Explain When the distance of the flashlight from the board (B) is doubled and tripled, what happens to the areas and intensities of the squares?

Using Radiation TEKS 3D What are some practical uses of radioisotopes? Research into safe use of radiation has impacted society and the environment. Radioisotopes are used to analyze matter, study plant growth, diagnose medical problems, and treat diseases.

Analyzing Matter Scientists use radiation to detect trace amounts of elements in samples. The process is called neutron activation analysis. A sample is bombarded with neutrons from a radioactive source. Some atoms in the sample become radioactive. The half-life and type of radiation emitted can be detected and analyzed by a computer. Because this data is unique for each isotope, scientists can determine what radioisotopes were produced and infer what elements were in the original sample. Museums use this process to detect art forgeries. Crime laboratories use it to analyze gunpowder residues.

Using Tracers Radioisotopes called tracers are used in agriculture to test the effects of herbicides, pesticides, and fertilizers on plants. A tracer is intro- duced into the substance being tested. Next, plants are treated with the tagged substance. Devices that detect radioactivity are used to locate the substance in the plants. The tracer may also be monitored in animals that consume the plants, as well as in water and soil.

766 Chapter 21 • Lesson 4 Diagnosing Medical Problems Radioisotopes can be used to detect disorders of the thyroid gland, which is located in the throat. The main function of this gland is to control the rate at which your cells release energy from food. The thyroid gland extracts iodide ions from blood and uses them to make the hormone thyroxine. To diagnose thyroid disease, the patient is given a drink containing a small amount of the radioisotope iodine-131. After about two hours, the amount of iodide uptake is measured by scanning the patient’s throat with a radiation detector. Figure 21.17 shows the results of such a scan. In a similar way, the radioisotope technetium-99m is used to detect brain tumors and liver disorders. Phosphorus-32 is used to detect skin cancer.

Treating Diseases Radiation is one method used in the treatment of some cancers. Cancer is a disease in which abnormal cells in the body are produced at a rate far beyond the rate for normal cells. The mass of cancer cells that result from this runaway growth is called a tumor. Fast-growing cancer cells are more susceptible to damage by high-energy radiation such as gamma rays than are healthy cells. Thus, radiation can be used to kill the cancer cells in a tumor. Some normal cells are also killed, however, and cancer cells at the center of the tumor may be resistant to the radiation. Therefore, the benefits of the treatment and the risks to the patient must be carefully evaluated before radiation treatment begins. Cobalt-60 and cesium-137 are typical radiation sources for cancer therapy. Salts of radioisotopes can also be sealed in gold tubes and directly inserted in tumors. This method of treatment is called seeding. The salts Figure 21.17 Radioactive Tracer emit beta and gamma rays that kill the surrounding cancer cells. Because This scanned image of a thyroid the radioisotope is in a sealed container, it is prevented from traveling to gland shows where radioactive other parts of the body. iodine-131 has been absorbed. Prescribed drugs containing radioisotopes of gold, iodine, or phosphorus Doctors use these images to identify are sometimes used in radiation therapy. For example, a dose of iodine-131 thyroid disorders. larger than that used to detect thyroid diseases can be given to a patient to treat the disease. The radioactive iodine passes through the digestive system into the blood, which carries it to the thyroid. The iodine that collects in the gland emits beta particles and gamma rays , which provide therapy.

21.4 LessonCheck TEKS 3D 28. Compare In each of the three detection 32. Infer Why do airports use scintillation counters devices described in the lesson, what is used to and not Geiger counters to search for radioactive detect the radiation? materials? 29. Evaluate What are four ways that research into 33. Compare Of Geiger counters, scintillation radioisotopes impacts society or the environment? counters, and film badges, which device is most similar to a smoke detector? Explain your choice. 30. Define Why is the radiation emitted by radioisotopes called ionizing radiation? 34. Sequence Briefly describe the three steps that occur when iodine-131 is used to diagnose thy- 31. Explain Suppose you worked with or near a radia- roid disease? tion source. Why might your employer use a film badge rather than a Geiger counter to monitor your 35. Explain What is one advantage of using sealed environmental exposure to radiation? tubes, or seeds, to treat a tumor?

Nuclear Chemistry 767 Y TH PL E P

A TEKS Chemystery 12B

An Ice-Age Baby Scientists were able to use carbon-14 dating to determine the age of the baby mammoth discovered in 2007. During Lyuba’s short time on Earth, the ratio of carbon-14 to other carbon isotopes in her body was constant. After she died, the unstable carbon-14 atoms began to decay. The other carbon atoms in Lyuba’s body remained stable. The ratio of carbon-14 atoms to other carbon atoms was no longer fixed. Based on the ratio of carbon isotopes in the preserved sample, Lyuba lived and died about 40,000 years ago. Archaeologists use the same method to date artifacts left behind by ancient cultures. An artifact is an object made or shaped by humans. Examples of artifacts are tools, weapons, and ornaments. Ancient cultures made the objects from natural materials in their environment—materials that they found, grew, or hunted. Artifacts containing carbon and made of materials from once-living materials can be analyzed using carbon-14 dating. Such artifacts include ax handles or bowls made of wood, arrowheads shaped from bone, or ornaments made from the shells of mussels or oysters.

1. Calculate Approximately how many half-lives 5. Calculate The half-life for carbon-14 is does 40,000 years represent? The half-life for 5730 years. About what percentage of the carbon-14 is 5730 years. original carbon-14 in a wooden bowl artifact would be left after 60,000 years? 2. Apply Concepts Archaeologists find a wooden bowl, a stone arrowhead, and a bone bead at a 6. Evaluate Data Thorium-234, which emits beta site that they suspect is about 40,000 years old. and gamma radiation, has a half-life of 24.1 days. Which objects can they use to test their hypoth- Considering Lyuba’s carbon-14 age of about esis? Explain. 40,000 years, why would thorium-234 be less useful than carbon-14 to determine Lyuba’s age? 3. Explain Describe what happens to the structure of carbon-14 atoms as this isotope decays. 7. Organize Data Radon-222, radium-226, uranium-235, and uranium-238 are naturally- 4. Write Balanced Nuclear Equations Use your occurring radioisotopes. Do research to find understanding of the radioactive decay processes the half-life of each radioisotope and what kind to write a balanced nuclear equation for the of radiation each radioisotope emits. Organize decay of carbon-14 to nitrogen-14. your data as an entry in a science journal.

768 Chapter 21 • CHEMystery Math Tune-Up: Nuclear Reactions TEKS 12B

Problem ➊ Analyze ➋ Calculate ➌ Evaluate

Plutonium-239 Knowns: The mass number of X must The mass numbers decays by emitting mass number of Pu = 239 equal the mass number of Pu total 239 on an alpha particle. mass number of α = 4 minus the mass number of α. both sides of the Balance the equation atomic number of Pu = 94 The atomic number of X must equation. The atomic by identifying the atomic number of α = 2 equal the atomic number of Pu numbers total 94 product of this minus the atomic number of α. on both sides of Unknowns: reaction. 239 4 239−4 the equation. The Mass number of X = ? 94Pu 2He + 94−2X 239 4 4 235 isotope uranium-235 94 2 + = 2 + 92 Pu He X Atomic number of X ? He X is a well-known Identity of X = ? The element with atomic radioisotope. Hint: Review Sample In an equation for a nuclear number 92 is uranium. Problem 21.1 for help reaction, mass numbers and 239 4 235 94 2 + 92 with balancing nuclear atomic numbers must be Pu He U equations. balanced.

Thorium-234 has a Knowns: Divide the decay time by the After three half-lives, half-life of 24.1 days. Original mass of Th = half-life of thorium to find the number of atoms If a thorium-234 6.4 × 10−12 g the number of half-lives. of a radioisotope will 1 sample has a mass of Decay time = 72.3 days decrease to 8 of the −12 72.3 days 6.4 × 10 g, how t1 = 24.1 days original number. 2 = 3 half-lives much of the sample is 24.1 days/half-life Unknown: left after 72.3 days? Review Sample Mass of Th remaining = ? Multiply the mass of thorium Hint: 1 by 2 three times. Problem 21.2 for The mass of thorium-234 another calculation 1 1 1 decreases by half with each 6.4 × 10−12 g × × × = involving half-life. half-life. Find the number of 2 2 2 × −13 half-lives in 72.3 days and 8.0 10 g multiply the mass of thorium 1 by 2 for each half-life.

Carbon-14 (C-14) Knowns: A ratio of C-14 atoms to N-14 The bone sample undergoes beta t1 = 5730 yr atoms of 1 means that C-14 has is 11,460 years old, 2 4 decay and produces Ratio of C-14 to N-14 = 25% decayed for two half-lives: which is equal to two nitrogen-14 (N-14). half-lives or the time 1 1 1 1 2 The half-life for this Unknown: = × = required for 75% of = 4 2 2 (2) process is 5730 years. Age of sample ? the carbon-14 atoms In a sample from an The number of C-14 atoms Convert two half-lives to years. to decay. ancient piece of bone, decreases by half every 5730 5730 years × 2 = 11,460 years the ratio of carbon-14 years. Find the number of atoms to nitrogen-14 half-lives that reduce the atoms is 25%. How 1 number of C-14 atoms to 4 old is the bone? (25%) and multiply by 5730.

Math Tune-Up 769 21 TEKS Practice TEKS 12B, 12A, 12C, 3D, 2H, 3F *Solutions appear in Appendix C Review Content *44. What happens to an atom with a nucleus that falls outside the band of stability? 36. Explain how radioisotopes are different from 45. Describe radioactive decay process by writing other isotopes. a balanced nuclear equation for the radioactive 37. The decay of radium-226 produces an isotope decay of fluorine-17 by positron emission. of the element radon and alpha radiation. The 46. Identify the more stable isotope in each pair. atomic number of radium (Ra) is 88; the atomic 14 13 a. 6C, 6C number of radon (Rn) is 86. Describe this 3 1 b. 1H, 1H radioactive decay process by writing a balanced 15 16 c. 8O, 8O nuclear equation. 13 14 d. 7 N, 7 N 38. An isotope of the element lead (Pb) decays to an * 47. Define half-life. isotope of the element bismuth (Bi) by emission of a beta particle. Complete the equation for 48. Why is it important that radioactive isotopes the reaction by supplying the missing atomic used for diagnosis or treatment of medical number and mass number. problems have relatively short half-lives? 210 ? 0 49. ?Pb 83 Bi + − 1e * A patient is given 20 mg of iodine-131. The half- life of iodine-131 is 8 days. How much of the 39. Write the symbol and charge for each item. isotope will remain in the patient’s body after a. alpha particle 40 days? b. beta particle c. gamma ray 50. What is the difference between natural and artificial radioactivity? *40. Alpha radiation is emitted during the decay of the following isotopes. Describe each radioac- 51. What are the transuranium elements? Why are tive decay process by writing a balanced nuclear they unusual? equation for it. Name the element produced in 52. Describe the process of nuclear fission, and each case. define a nuclear chain reaction. a. 238 c. 235 uranium-238 ( 92U) uranium-235 ( 92U) 53. Why are spent fuel rods removed from a reactor b. 230 d. 222 thorium-230 ( 90 Th) radon-222 ( 86Rn) core? What do they contain? What happens to 41. The following radioisotopes are beta emitters. them after they are removed? Write balanced nuclear equations to describe 54. Fusion reactions produce enormous amounts each decay process. of energy. Why is fusion not used to generate 14 40 a. carbon-14 ( 6C) c. potassium-40 (19K) electrical power? 90 b. strontium-90 (38Sr) 55. Why are X-rays and the radiation emitted by *42. How are the mass number and atomic num- radioisotopes called ionizing radiation? ber of a nucleus affected by the loss of the 56. following? Why must people rely on devices such as Geiger counters to detect radiation? a. beta particle b. alpha particle 57. What type of jobs require people to wear a film c. gamma ray badge and what is the purpose of this device? 43. The following radioactive nuclei decay by emit- 58. Why are cancer cells more easily damaged by ting alpha particles. Write the product of the high-energy radiation than healthy cells are? decay process for each isotope. 238 210 a. 94Pu c. 84Po 210 230 b. 83Bi d. 90 Th

770 Understand Concepts 64. Write a balanced nuclear equation for each word equation. * 59. Write balanced nuclear equations for these a. Radon-222 emits an alpha particle to form transmutations. polonium-218. 30 30 b. Radium-230 is produced when thorium-234 a. 15P to 14Si 13 14 emits an alpha particle. b. 6C to 6C 131 131 c. When polonium-210 emits an alpha particle, c. 53 I to 54 Xe the product is lead-206. 60. How are the nuclear reactions that take place in 65. Research and describe the contributions the the sun different from the nuclear reactions that following scientists made to the study of take place in a nuclear reactor? radioactivity and nuclear chemistry. 61. Complete these nuclear equations. a. Marie Curie 32 0 a. 15P + − 1e b. Antoine Henri Becquerel 14 0 b. 7 N + − 1e c. James Chadwick 238 234 c. 92 U 90 Th + d. Ernest Rutherford 141 0 d. 56Ba + − 1e 66. 181 4 How many protons and how many neutrons are e. 77Ir + 2 He in each of the following nuclei? 60 206 233 3 62. Write nuclear equations for the beta decay of a. 27Co b. 82Pb c. 90 Th d. 1H the following isotopes. 67. A sample of matter has 32 million radioactive 90 14 137 239 50 * a. 38Sr b. 6C c. 55Cs d. 93 Np e. 22 Ti atoms. How many of these atoms would be left 63. The graph shows the radioactive decay curve for after five half-lives? thorium-234. Use the graph to answer the ques- 68. Write balanced nuclear equations for alpha tions below. emission by each of these isotopes. 231 241 226 252 a. 91Pa b. 95Am c. 88Ra d. 99Es Thorium-234 Decay *69. Write balanced nuclear equations for beta emis- 100 sion by each of these isotopes. %)

( 3 28 131 75 a. 1H b. 12Mg c. 53I d. 34Se 80 70. Use the concept of stability to compare chemi- 60 cal reactions with nuclear reactions.

40 71. The ratio of carbon-14 to carbon-12 in a chunk of charcoal from an archaeological dig is one- 20 half the ratio of carbon-14 to carbon-12 in a piece of freshly cut wood. How old is the chunk Radioisotope remaining 0 20 40 60 80 100 120 of charcoal? Days 72. How are a positron and an electron similar? How are they different? a. What percentage of the isotope remains after *73. Use what you know about balanced nuclear 60 days? equations to complete the following equations. b. After 40 days have passed, how many grams 38 38 a. 19K 20Ca + ? of a 250-g sample of thorium-234 would 242 4 b. 94Pu ? + 2He remain? 68 0 c. 31Ga ? + − 1e c. From the trend in the data, predict how long 68 68 d. 32Ge 31Ga + ? it would take in days for 44 g of thorium-234 to decay to 4.4 g of thorium-234. d. What is the half-life of thorium-234?

Nuclear Chemistry 771 83. Calculate Bismuth-209 was bombarded with 266 iron-58 for several days. Meitnerium (109 Mt) was TEKS Practice produced. How many neutrons were released Think Critically per atom of meitnerium? 209 58 266 1 83Bi + 26Fe 109 Mt + ? 0n 74. Classify Name the elements represented by the * 84. Predict When neutrons strike magnesium-24 following symbols and indicate which of them * 24 (12Mg), a neutron is captured and photons are would have no stable isotopes. ejected. What new element is formed? a. Pt b. Th c. Fr d. Ti 85. Generalize About Alpha Radiation 75. Analyze Data Use the graph to determine Plutonium-239 emits alpha particles, which which of these isotopes have stable nuclei: do not penetrate a thin sheet of paper or skin. neon-21, zirconium-90, and neodymium-130. Under what conditions would plutonium-239 be especially hazardous for organisms? Ratio of Neutrons to Number of Protons for Stable Nuclei *86. Calculate Tritium (hydrogen-3) has a half-life of 12.3 years. How old is a bottle of wine if the 140 Ratio≈1.5 tritium content is 25% that of new wine? 120 Band of stability 87. Apply Concepts What properties of isotopes 100 Ratio≈1.3 make it possible to use neutron activation 80 analysis to identify the composition of matter? Ratio≈1.2 60 88. Research and Describe the History of n0 1 = 40 p + 1 Chemistry What effect did the discovery of

Number of neutrons radioactivity have on Dalton’s atomic model? 20 (Ratio = 1.0) 89. Analyze Data A sample of californium-249 0 249 20 40 60 80 100 120 ( 98Cf) was used as the target in the synthesis of 236 Number of protons seaborgium (106Sg). Four neutrons were emitted 249 for each transformed 98Cf atom. The result was a 76. Use Analogies Compare an element’s half-life nucleus with 106 protons and a mass of 263 amu. to a single-elimination sports tournament. What type of particle struck the target? 249 1 263 7 7. Make Inferences A radioactive nucleus decays 98Cf + ? 4 0n + 106Sg 211 to give a bismuth-211 ( 83Bi) nucleus and an 90. Use Models Explain how the falling dominoes alpha particle. What was the original nucleus? in the photograph can be used as a model for a *78. Calculate The carbon-14 content of an object chain reaction. produces 4 counts per minute per gram of carbon. Living matter has a carbon-14 content that produces 16 counts per minute per gram of carbon. What is the age of the object? 79. Compare Radiation Why is an alpha particle less penetrating than a beta particle? 80. Evaluate the Impact How did Becquerel’s research impact the scientific thought of Marie and Pierre Curie? 81. Compare and Contrast Iodine-131 is used to diagnose and treat thyroid disorders. What is the main difference between the two processes? 82. Apply Concepts Should a radioisotope with a half-life measured in days be used in a smoke detector? Why or why not?

772 Chapter 21 • TEKS Practice Enrichment Write About Science

91. Calculate The radioisotope cesium-137 has a 98. Evaluate the Impact of Research on Society half-life of 30 years. A sample decayed at the Research methods used to date materials such rate of 544 counts per minute in the year 1985. as pottery, coral, and stone. Communicate In what year will the decay rate be 17 counts per your valid conclusions by preparing an oral minute? report that summarizes your findings on the radioisotopes used, their half-lives, and their 92. Analyze Data Use the graph below to answer limitations. Also include in your report how the questions. this research impacts society. a. Describe the process that is being depicted in the graph. 99. Explain Research how technetium-99m is b. Suggest an appropriate title for the graph. produced. What does the letter m at the end of its name stand for? How is the isotope used in ? bone imaging?

Cumulative Review %) C-14 N-14 100. How many protons, neutrons, and electrons are in an atom of each isotope?

Isotope ( a. iron-59 b. uranium-235 c. chromium-52 Time in years 101. What is the Pauli exclusion principle? What is Hund’s rule? 93. Write Balanced Nuclear Equations 102. Bismuth-211 decays by alpha emission to yield Identify the bonds between each pair of atoms another radioisotope, which emits beta radia- as ionic or covalent. tion as it decays to a stable isotope. Write a. carbon and silicon balanced nuclear equations for the nuclear b. calcium and fluorine reactions and name the decay products. c. sulfur and nitrogen d. bromine and cesium 94. Analyze Data What isotope remains after three beta particles and five alpha particles are 103. The diagram below shows a water molecule. lost from a thorium-234 isotope? Identify the location of any partial positive and partial negative charges on the molecule. Then 95. Evaluate In the following argument, the third explain how the partial charges and their loca- statement is based on the first two statements. Is tions produce an attraction between different the reasoning logical? Why or why not? water molecules. (1) Radiation kills fast-growing cells. (2) Cancer cells are fast-growing. (3) Therefore, radiation kills only cancer cells. O *96. Calculate Uranium has a density of 19 g/cm3. What volume does a mass of 8.0 kg of uranium HH occupy? 9 7. Write Balanced Nuclear Equations Element 107 (Bh) is formed when nuclei of element 109 (Mt) each emit an alpha particle. Nuclei of ele- *104. A piece of magnesium with a mass of 10.00 g is ment 107, in turn, each emit an alpha particle, added to sulfuric acid. How many cubic centi- forming an atom with a mass number of 262. meters of hydrogen gas (at STP) will be pro- Write balanced nuclear equations for these two duced if the magnesium reacts completely? How nuclear reactions. many moles of hydrogen gas are in this volume?

Nuclear Chemistry 773 IEW TH V E E

R TEKS Practice TEKS Chapter 21 105. Balance the following equations. Lesson 21.1 a. Ca(OH)2 + HCl CaCl2 + H2O In Lesson 21.1, you learned that unlike chemical reactions, nuclear reactions are not affected by changes b. Fe2O3 + H2 Fe + H2O c. NaHCO + H SO in temperature, pressure, or the presence of catalysts. 3 2 4 Also, nuclear reactions of a given radioisotope cannot Na2SO4 + CO2 + H2O be slowed down, sped up, or stopped. In addition, three d. C2H6 + O2 CO2 + H2O types of nuclear radioactive decay are alpha, beta, and gamma radiation. *106. You have a 0.30M solution of sodium sulfate. What volume (in mL) must be measured to give Readiness TEKS: 12B 0.0020 mol of sodium sulfate? Supporting TEKS: 12A TEKS: 3D 107. Draw the structural formula for each compound. Lesson 21.2 In Lesson 21.2, you learned that the neutron- a. 2,2-dimethylhexane to-proton ratio in a radioisotope determines the type b. 1,2-dimethylcyclopentane of radioactive decay that occurs. During each half-life, c. 2-methyl-2-heptene half of the remaining radioactive atoms decay into d. 2-butyne atoms of a different element. Transmutation can occur e. 1,4-dimethylbenzene by radioactive decay or when particles bombard the f. 3-ethyloctane nucleus of an atom. 1 n half-life equation: A = A × 108. Draw a condensed structural formula for each 0 ( 2) compound. Readiness TEKS: 12B a. 1,2-dimethylcyclobutane Supporting TEKS: 12A b. 2-methyl-2-pentene TEKS: 2H, 2I c. 2-butene d. 2-pentyne Lesson 21.3 In Lesson 21.3, you compared fission and fusion. You e. 2-methylhexene learned that in a chain reaction, some of the emitted 109. Is petroleum or coal more likely to be a good neutrons react with other fissionable atoms, which emit neutrons that react with more fissionable atoms. Fusion source of aromatic compounds? reactions, in which small nuclei combine, release much 110. Which of these statements applies to ethene? more energy than fission reactions, in which large nuclei split apart to form smaller nuclei. a. saturated hydrocarbon b. H—C—H bond angle of 120° Supporting TEKS: 12C c. alkene Lesson 21.4 d. aromatic compound In Lesson 21.4, you learned that Geiger counters, scintillation counters, and film badges are commonly used to detect radiation in the environment. Research involving the use of radioisotopes affects society by allowing people to analyze the composition of matter, study plant growth, diagnose medical problems, and treat diseases. TEKS: 3D, 2I

If You Have Trouble With . . . Question 100 101 102 103 104 105 See Lesson 4.3 5.2 8.1 8.4 10.2, 12.2 11.1 Question 106 107 108 109 110 See Lesson 16.2 20.1–20.4 20.1–20.4 20.5 20.2

774 Chapter 21 • TEKS Practice ★ TEKS Practice: Chapter Review

1 How does a beta particle differ from an electron that is given up during the formation of an ionic compound?

A A beta particle does not have mass.

B A beta particle has a different electric charge.

C A beta particle is not attracted to the protons inside the nucleus.

D A beta particle results from a reaction inside the nucleus of an atom.

2 Jordan created the following table based on information from a scientific article about the history of nuclear power.

Characteristics of Some Types of Radiation

Type Consists of Symbol Charge Mass (amu)

Alpha particles Alpha radiation α, 4 2+ 4 (helium nuclei) 2He Beta particles Beta radiation β, 0 1− 1/1837 (electrons) −1e High-energy Gamma radiation electromagnetic γ 0 0 radiation

Jordan noticed that an alpha particle has the same chemical symbol as helium, with the same mass and atomic numbers. How does an alpha particle differ from an atom of helium gas?

F An alpha particle does not occur in nature.

G An alpha particle has a different nuclear structure than helium.

H An alpha particle has a different number of protons than helium.

J An alpha particle contains fewer electrons than helium.

Nuclear Chemistry 775 3 Lead-214 decays to bismuth-214 as described in the following reaction.

214 214 82Pb 83Bi + ?

Which particle is necessary to complete the equation?

4 A 2He

0 B −1e

0 C +1e

1 D 0n

4 Which equation represents a nuclear reaction in which potassium-40 captures an electron to form a more stable isotope?

40 0 40 F 19K ++ 1e 20Ca

40 0 40 G 19K + − 1e 18Ar

40 4 44 H 19K + 2He 21Sc

40 40 0 J 19K 18Ar ++ 1e

5 How do the reactant isotopes in fission reactions differ from those in fusion reactions?

A Fission reactant isotopes do not split apart during the reaction.

B Fission reactant isotopes are more stable than fusion reactant isotopes.

C Fission reactant isotopes have much greater mass and atomic numbers.

D All of the above

776 Chapter 21 • TEKS Practice ★ TEKS Practice: Cumulative Review

6 In an electrochemical cell, iron is oxidized to iron(II) ions, and copper(II) ions are reduced to copper metal. What is the balanced chemical equation for this reaction?

F Fe2−(aq) + Cu2+(aq) Cu(s) + Fe(s)

G Fe(s) + Cu2+(aq) Cu(s) + Fe2+(aq)

H Cu(s) + Fe2+(aq) Fe(s) + Cu2+(aq)

J 2Fe(s) + Cu2+(aq) 2Cu(s) + Fe2+(aq)

7 What is the condensed structural formula for 4-ethyl-2,3-dimethylheptane?

CH3 CH CH CH CH2 CH2 CH3

A CH2 CH2 CH3

CH3 CH3

CH3 CH CH CH CH2 CH2 CH3

B CH3 CH3 CH2

CH3

CH3 CH2 CH3 C C C CH3 CH2 CH CH2 CH2 CH3

CH3

CH3 CH CH CH CH2 CH3

D CH2 CH2 CH3

CH3 CH3

If You Have Trouble With . . . Question 1 2 3 4 5 6 7 See Lesson 21.1 21.1 21.2 21.2 21.3 19.3 20.1 TEKS 12A 12A, 3B 12B 12B 12C 8D 7B

Nuclear Chemistry 777