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21Nuclear Chemistry 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 pen- etrating 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.
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