Unit 12 - Nuclear Chemistry Notes & CW

Transcription

1 Name: Unit 12 - Nuclear Chemistry Notes & CW Unit Objectives Upon completion of the unit students should be able to: Predict the stability of an isotope based on the ratio of neutrons and protons in its nucleus. Understand that while most nuclei are stable some are unstable and spontaneously decay emitting radiation. Calculate the initial amount of the fraction remaining, or the half life of a radioactive isotope, using the half life equation. Understand the concept of half life. Differentiate between the following emissions based on mass, charge, ionizing power, and penetrating power: Alpha, Beta, Positron, and Gamma Determine the type of decay (alpha, beta, positron, and gamma) and write the nuclear equations. Compare and contrast fission and fusion reactions Distinguish between natural and artificial transformations. Complete nuclear equations and predict missing particles from nuclear equations. Understand the change in energy in a nuclear reaction. Be aware of the risks associated with radioactivity. Recognize the beneficial uses and real world application of radioactive isotopes. Radioactive dating Tracing chemical and biological processes Industrial measurement Nuclear power Detection and treatment of diseases Focus Questions for the Unit: What determines nuclear stability? How does an unstable element stabilize? YOU SHOULD BE ABLE TO ANSWER THESE IN DETAIL BY THE END OF THE UNIT Define the following vocabulary: Artificial transmutation Nuclear fusion Atomic Mass Unit (amu) Average Weighted Mass Atomic number Tracer Half-life Isotope Mass number Radioactivity (Radioactive Decay) Nuclear charge Nuclear fission 1

2 The bold, underlined words are important vocabulary words that you should be able to define and use properly in explanations. This is a study guide for what you will be tested on throughout the year. The objectives are divided into categories of Knowledge (what you have to know) and Application (what you have to be able to do). Knowledge I. NUCLEAR CHEMISTRY Application 1. o o o The stability of an isotope is based on the ratio of the neutrons and protons in the nucleus. Usually when the ratio is not 1:1, the nucleus gets a little unstable and starts spitting out particles so that it will have a more stable 1:1 ratio. Although most nuclei are stable, some are unstable and spontaneously emit radiation. We call these unstable isotopes radioactive isotopes, radioisotopes, or nuclides. 2. o o o Spontaneous decay (natural emission of radiation) by a nuclide (radioactive isotope) involves the release of particles and/or energy from the nucleus. Each radioactive isotope has a specific decay mode (the kind of particle or energy it gives off from its unstable nucleus) (Tables N and O!) alpha decay: release of alpha particles beta decay: release of beta particles positron emission: release of positrons gamma radiation : release of gamma rays These emissions differ in mass, charge, ionizing power, and penetrating power. o o Determine decay mode and write nuclear equations showing alpha decay, beta decay, positron emission, and gamma radiation (*Remember to put radioactive emissions on the RIGHT side of the arrow if something is released, it goes on the right) Compare and contrast the 4 different types of radiation in terms of mass, charge, ionizing power, and penetrating power. 3. o Each radioactive isotope has a specific half-life (rate of decay). The half-life is the time it takes for half of the radioisotope to decay/transmute into something more stable). (Table N) o Calculate the initial amount, the fraction remaining, time elapsed, or the half-life of a radioactive isotope, given the other variables 4. o o Nuclear reactions are represented by equations that include symbols for elements and radioactive emissions (with mass number in upper left and charge/atomic number in lower left) These reactions show conservation of mass and charge o o Complete nuclear equations and predict missing particles in nuclear equations Write nuclear equations given word problems 2

3 5. o A change in the nucleus of an atom that changes it from one element to another is called transmutation. This can occur naturally or can be done artificially by bombarding the nucleus with high-energy particles. o Distinguish between natural transmutation (one reactant) and artificial transmutation (two reactants) given nuclear equations 6. o Types of nuclear reactions include fission and fusion. Fission and fusion can be natural or artificial transmutations. o o Compare and contrast fission and fusion reactions. Distinguish between fission and fusion reactions given nuclear equations 7. o o Nuclear changes convert matter into energy (E = mc 2 ) Energy released during nuclear reactions is much greater than the energy released during chemical reactions. o o Compare and contrast chemical reactions and nuclear reactions Describe benefits of using nuclear fission 8. o There are risks and problems associated with radioactivity and the use of radioactive isotopes, including: biological exposure, long-term storage and disposal problems, and nuclear accidents which release radioactive materials into the environment. o Describe the risks and problems associated with using radioactive isotopes 9. o In addition to using nuclear fission for nuclear power, radioactive isotopes have other beneficial uses in medicine and industrial chemistry, including: radioactive dating (ages of once-living things can be found from the ratio of C-14 to C-12 in the remains; ages of rocks can be found from the ratio of U-238 to Pb-206) tracing chemical and biological processes (radioactive tracers can be injected into the body and then x-rayed. The radioactive substance will show up on the x-ray and if there are problems, they can be detected easily) detecting and treating of disease (Sr-90: diagnosing and treating bone cancer; I-131: diagnosing and treating thyroid disorders; Co-60: cancer treatment radiation can be used to kill bacteria in foods (used with spices, meats, produce) 3

4 Lesson 1: Stability & Radioactivity Review: Isotopes are Stability of Nuclei: Large atoms are considered elements with an atomic > 83. They are In small atoms the nucleus is stable and therefore are o Exception to Small Atom Rule: - Nuclear Chemistry is the Example: C-12 & C-14 Natural radioactivity occurs when nuclei are unstable. For any element, an isotope that is unstable is called a radioisotope. A Geiger counter can be used to detect radiation given off by radioactive isotopes. 4

5 Classwork 12-1: Nuclear Stability Isotopes: Some elements come in several different forms. Take uranium, for example. Most uranium is uranium It has 92 protons and 146 neutrons ( = 238). But there are several other kinds of uranium. They all have 92 protons, but the number of neutrons differs. They are isotopes of uranium. Some isotopes are more stable then others. These unstable isotope called radioisotopes and will decay spontaneously to form more stable products. As a general rule the following isotopes are radioisotopes or unstable:. Any isotopes with an atomic number greater than 83 is naturally radioactive.. When an isotope has a mass that is not its typical mass (the mass on the reference table) is radioactive. Fill out the chart. Give the correct number of protons, atomic notation, and predict the stability of each isotope. Unstable 5

6 Lesson 2: Half-Life Radioactive substances decay at a rate that is The Half-life is the The shorter the half life of an isotope the less stable it is. The longer the half life of an isotope the more stable it is. Table N lists common radioactive isotopes as well as their half-lives and modes. Example: A sample of I-131 decays to 1.0 grams in 40 days. What was the mass of the original sample? Half-life of I-131 from Table N =8.07 days. 40days/8 days=5 half life decays ½ ½ ½ ½ ½ 1.0g 2.0g 4.0g 8.0g 16.0g 32.0g Example: What is the total number of hours required for Potassium-42 to undergo three half life periods? From Table N K-42 half life=12.4 hours 12.4 hours x 3= 37.2 hours Example: What mass of a 32.0 g sample of 32 P will remain after 71.5 days of decay? From Table N half-life of P-32=14.3days 71.5 days/14.3 days=5 half lives ½ ½ ½ ½ ½ 32.0g 16.0g 8.0g 4.0g 2.0g 2.0g Radioisotopes are used for various things: 6

7 Smoke detectors C-14 Medical Applications Must have Tc-99/Co-60 I-131 Dangers of radioactivity Check your understanding 1) After 60 days, 10.0 grams of radioactive isotope remains from an original 80.0 g sample. What is the half life of this element? 2) In a nuclear reaction, the particle may be spontaneously released from the nucleus of an atom resulting in the transmutation of the atom into another element. a) According to the Selected Radioisotopes table, what is the half life of C-14? b) What mass of 10.0 g sample of C-14 remains after 11,460 years have evolved? 3) A radioactive element has a half life of 2 days. What is the fraction of the original sample will remain after six days? 7

8 Virtual Lab: How can you simulate the radioactive halflife of an element? This lab is located at: Background Information: The rate of decay of a radioactive isotope of an element is measured in terms of its halflife. When a radioactive isotope decays, the decayed atoms form a daughter product. The halflife of a radioactive element is the time it takes for half of its atoms to decay into the daughter product. After two half-lives, one-fourth of the original isotope s atoms remain, and three-fourths have turned into the daughter product. After many more half-lives, a very small amount of the original parent isotope remains, and almost all of it has decayed into the daughter product. Each radioactive isotope has its own characteristic half-life. For instance, the naturally occurring radioactive isotope of uranium (U-238) decays into thorium-234 with a half-life of 4.5 billion years. This means that half of the original amount of uranium-238 still remains after this time. In contrast, some radioactive isotopes decay quickly. For instance, polonium-214 has a half-life of seconds! Objectives: In this Virtual Lab you will investigate the meaning of radioactive half-life as you see a simulation of the radioactive decay of isotopes of four hypothetical elements. Procedure: Collect radioactive decay rate data for hypothetical isotopes over a period of 20,000 years. Determine, compare, and contrast half-lives of four radioactive elements. 1. Click the Video button. Watch the video to find out about atoms. Write your observations in the Journal. 2. Select one of the four elements from the pull down menu. Note: At first you will see 100 radioactive atoms on the screen. 3. Click the Years Passed button to advance the time 1000 years. 4. Click the Count the Remaining Radioactive Atoms button to see how many radioactive atoms remain. 5. At any time you can click the Remove Atoms No Longer Radioactive button to remove the daughter atoms. 6. Record your data in the data table. 7. Continue to advance the time by 1000-year intervals until you have determined the half-life of the element. 8. After you have completed the Table for the element you chose, click the Graph button to plot your data. 9. Repeat these steps for the three remaining elements. 10. Complete the Questions. 8

9 Data Table: Remaining Radioactive Atoms Years Element A Element B Element C Element D 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 11,000 12,000 13,000 14,000 15,000 16,000 17,000 18,000 19,000 20,000 Questions: 1) According to your data, what are the approximate half-lives of the elements A, B, C, and D? A: B: C: D: 2) What part of an original isotope s number of atoms remains have two half-lives? 3) What happens to a radioactive isotope as it decays? Does the radioactive material disappear? Explain. 4) After three half-lives of an isotope, 1 billion (one-eighth) of the original isotope s atoms still remain in a certain amount of this element. How many atoms of the daughter product would you expect to be present? 9

10 Classwork 12-2: Use the chart below as a template to solve every half-life problem Example: 1.00 g 20 minutes 40 minutes 60 minutes 80 minutes 0.5 g 0.25 g g g 100 minutes 10

11 1. How long does it take a g sample of Au-l 98 to decay to 6.25g? 2. How many half-lives will pass by the time a 60.0g sample of Co-60 decays to 7.5g? 3. How long does it take a 180g sample of Au-198 to decay to 1/8 its original mass? 4. What fraction of a sample of N-16 remains undecayed after seconds? 5. What is the half-life of a radioactive isotope if a 500.0g sample decays to 62.5g in 24.3 hours? 6. What is the half-live of a radioactive isotope if it takes 6.2 days for a 72g sample to decay to 18g? 11

12 7. How many half-lives of K-37 will pass after 6.15 seconds? 8. What fraction of Pu-239 (an artificially produced isotope used as a fuel in some nuclear fission reactors) remains undecayed after 72,300 years? 9. If a g sample of I-131 decays to 43.75g, how much time has passed? 10. How long will it take a 3.5g sample of Fr-220 to decay so that only 1/4 of the original amount of Fr-220 remains? 11. What is the half-life of a radioisotope if 1/16 of it remains undecayed after 26.4 days? 12. If a radioactive sample of a pure material decays from 600g to 75g in 42.9 days, what radioisotope could be in the sample? 12

13 13. Co-60 is used in some cancer radiation therapies. What fraction of a sample of Co-60 will remain undecayed after years? 14. Sr-90 is a common waste product of nuclear fission reactors. How many half-lives of Sr-90 will pass after years? 15. How many years would it take for a 1.000g sample of U-238 to decay to about 3.9 mg? 16. If g of K-42 remains undecayed after hours, what was the original sample size? 17. What is the half-life of a radioactive isotope if 1/32 of it remains undecayed after 7.5 days? 18. If your cellar was measured to contain 2.400g of Rn-222 (a radioactive gas naturally produced by some granite deposits), how long would it take for that sample to decay to 0.15g? 13

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16 Classwork 12-2(con't): Uses for Radioisotopes Radiation is used by doctors to diagnose illness and helps archaeologists find the age of ancient artifacts. Electricity produced by nuclear fission - - splitting the atom - - is one of its greatest uses. A reliable source of electricity is needed to give us light, help to groom and feed us, and to keep our homes and businesses running. Let me give you some specific examples of how the radiation has been used to - - Diagnose and treat illnesses Kill bacteria and preserve food without chemicals and refrigeration Process sludge for fertilizer and soil conditioner Locate underground natural resources and tell a dry hole from a gusher Make smoke detectors, nonstick fry pans, and ice cream Grow stronger crops Power satellites and provide future electrical needs for space laboratories with people on board Design instruments, techniques, and equipment; measure air pollution Prove the age of works of art and assist in determining their authenticity RADIATION IN MEDICINE X- rays are a type of radiation that can pass through our skin. Our bones are denser than our skin, so when x- rayed, bones and other dense materials cast shadows that can be detected on photographic film. The effect is similar to placing a pencil behind a piece of paper and holding them in front of a light. The shadow of the pencil is revealed because most light has enough energy to pass through the paper, while the denser pencil stops all the light. The difference is that we need film to see the x- rays for us. Today, doctors and dentists use x- rays to see structures inside our bodies. This allows them to spot broken bones and dental problems. X- ray machines have now been connected to computers in the development of machines called CAT scanners. These instruments provide doctors with color TV pictures that show the shape of internal organs. Approximately 10 million nuclear medicine procedures are performed in the United States annually. Diagnostic x- rays and or radiation therapy were administered to about seven out of every 10 Americans. Medical procedures using radiation have saved thousands of lives through the detection and treatment of conditions ranging from hyperthyroidism to bone cancer. In such procedures, doctors administer slightly radioactive substances to patients, which are attracted to certain internal organs such as the pancreas, kidney, thyroid, liver, or brain, to diagnose clinical conditions. Moreover, radiation is often used to treat certain types of cancer. Radioactive iodine, specifically iodine- 131, is being used frequently to treat thyroid cancer, a disease which strikes about 11,000 Americans every year. RADIATION IN SCIENCE Radiation is used in science in many ways. Just as doctors can label substances inside people's bodies, scientists can label substances that pass through plants, animals, or our world. This allows us to study such things as the paths that different types of air and water pollution take through the environment. It has also helped us learn more about a wide variety of things, such as what types of soil different plants need to grow, the size of newly discovered oil fields, and the track of ocean currents. Scientists use radioactive substances to find the age of ancient objects by a process called carbon dating. For example, in the upper levels of our atmosphere, cosmic rays hit nitrogen atoms and form a naturally radioactive isotope called carbon- 14. Carbon is found in all living things, and a small percentage of this carbon is carbon- 14. When a plant or animal dies, it no longer takes in new carbon and the carbon- 14 it contains begins the process of radioactive decay. 16

17 However, new isotopes of carbon- 14 continue to be formed in our atmosphere, and after a few years the percent of radioactivity in an old object is less than it is in a newer one. By measuring this difference, scientists are able to determine how old certain objects are. The measuring process is called carbon dating. RADIATION IN INDUSTRY We could talk all day about the many and varied uses of radiation in industry and not complete the list. To make a long story short, we'll just concentrate on a few. Exposure to some types of radiation (for example, x- rays) can kill germs without harming the items that are being disinfected or making them radioactive. For example, when treated with radiation, foods take much longer to spoil, and medical equipment such as bandages, hypodermic syringes, and surgical instruments don't have to be exposed to toxic chemicals or extreme heat to be sterilized. Although we now use chlorine, a toxic and difficult- to- handle chemical, we may use radiation in the future to disinfect our drinking water and even kill all the germs in our sewage. Ultraviolet light is already being used to disinfect drinking water in some homes. The agricultural industry makes use of radiation to improve food production. Plant seeds, for example, have been exposed to radiation to bring about new and better types of plants. Besides making plants stronger, radiation can also be used to control insect populations, thereby decreasing the use of pesticides. Engineers use radioactive substances to measure the thickness of materials and an x- ray process called radiography to find hard to detect defects in many types of metals and machines. Radiography is also used to check such things as the flow of oil in sealed engines and the rate and way various materials wear out. And we've already talked about the use of the radioactive element uranium, which is used as a fuel to make electricity for our cities, farms, towns, factories, etc. In outer space, radioactive materials are also used to power spacecraft. Such materials have also been used to supply electricity to satellites sent on missions to the outermost regions of our solar system. Radiation has been used to help clean up toxic pollutants, such as exhaust gases from coal- fired power stations and industry. Sulfur dioxides and nitrogen oxides, for example, can be removed by electron beam radiation. As you can see, radiation and radioactive materials have played and will continue to play a very significant role in our lives. Let's sum up this discussion with a walk through the life of a typical family for one day and learn about some of the uses of radiation. Dad gets up in the morning and puts on a clean shirt. His polyester- cotton blend shirt is made from chemically treated fabric that has been irradiated (treated with radiation) before being exposed to a soil- releasing agent. The radiation makes the chemicals bind to the fabric, keeping his shirt fresh and pressed all day. The shirt is not radioactive. In the kitchen, Jenny is frying an egg. That nonstick pan she is using has been treated with gamma rays, and the thickness of the eggshell was measured by a gauge containing radioactive material before going into the egg cartoon. Thin, breakable eggs were screened out. The turkey Mom is taking out of the refrigerator for tonight's dinner was covered with irradiated polyethylene shrink- wrap. Once polyethylene has been irradiated, it can be heated above its usual melting point and wrapped around the turkey to provide an airtight cover. As Dad drives to work, he passes reflective signs that have been treated with radioactive tritium and phosphorescent paint. During lunch, brother Bob has some ice cream. The amount of air whipped into that ice cream was measured by a radioisotopic gauge. After you and your family return home this evening, some of you may have soda and others may sit and relax. Nuclear science is at work here: The soda bottle was carefully filled - - a radiation detector prevented spillover. And your family is safe at home because the ionizing smoke detector, using a tiny bit of americium- 241, will keep watch over you while you sleep. 17

18 1. How can we use radioactive isotopes to detect illness? 2. How can we use radiation to detect weakness in the construction of buildings? 3. Have you ever had a bone x- ray? Teeth x- rayed? How did this help your doctor or dentist treat you? 4. Do you think additional radiation received when people have medical x- rays, about 40 millirems per year, is worth the benefits they receive? 5. Are there advantages to using radiation instead of pesticides to control pests, such as insects? Multiple Choice: 1. The decay of which radioisotope can be used to estimate the age of the fossilized remains of an insect? 1. Rn I Co C Which radioisotope is used for diagnosing thyroid disorders? 1. U I Pb Co Cobalt- 60 and idodine- 131 are radioactive isotopes that are used in 1. Dating geological formations 2. Industrial measurements 3. Medical procedures 4. Nuclear power 4. Which radioactive isotope is used in treating cancer? 1. Carbon Lead Cobalt Uruanium

19 5. The course of a chemical reaction can be traced by using a 1. Polar molecule 3. Stable isotope 2. Diatomic molecule 4. Radioisotope Constructed Response: Base your answer to the next 3 questions on the information below and on your knowledge of chemistry. Cobalt- 60 is commonly used as a source of radiation for the prevention of food spoilage. Bombarding cobalt- 59 nuclei with neutrons produces the nuclide cobalt- 60. A food irradiation facility replaces the cobalt- 60, a source of gamma rays, when the radioactivity level falls to 1/8 of its initial level. The nuclide cesium- 137 is also a source of radiation for the prevention of food spoilage 1. Complete the nuclear equation below for the decay of cesium Your response must include the symbol, atomic number, and mass number of the missing particle Cs à 0 e Determine the total number of years that elapse before an original cobalt- 60 source in an irradiation facility must be replaced. 3. Identify one emission spontaneously released by a cobalt- 60 nucleus. 19

20 Lab Activity - Radioactive M&Ms Pre-Lab Questions: 1. On the periodic table, the number for carbon is, and the atomic mass is. What do each of these numbers tell us? 2. Give the term for an element that has the same atomic number, but different atomic mass:. 3. What particle in the nucleus is responsible for this difference in mass? 4. Some isotopes are stable. What does this mean? 5. Some isotopes are unstable. What does this mean? 6. What is the atomic mass number for the stable isotope of carbon? 7. What is the atomic mass number for the unstable isotope of carbon? 8. What is given off by unstable isotopes? 9. During radioactive decay, the isotope decays into a isotope that has a different number. Materials: M&M or Skittles candy pieces, resealable bag, graph paper 20

21 Procedures: 1. Place 50 atoms of candium (pieces of candy) in the bag. 2. Seal the bag and gently shake for 10 seconds. 3. Gently pour out candy. 4. Count the number of pieces with the print side up and record the data. These atoms have "decayed". 5. Return only the pieces with the print side down to the bag. Reseal the bag. 6. Consume the "decayed atoms. 7. Gently shake the sealed bag for 10 seconds. 8. Continue shaking, counting, and consuming until all the atoms have decayed. 9. Graph the number of undecayed atoms vs. time. Trial Number of Atoms Decayed Number of undecayed atoms remaining Class Total Class Average O

22 Graph: Conclusion: 1. What is a half-life? 2. In the experiment, what was the half-life of the element candium? 3. At the end of two half-lives, what fraction of the atoms had not decayed? If time allows complete Question 4 and/or 5 below 4. Describe the shape of the curve drawn. Repeat the experiment three more times, starting with 30 atoms, 80 atoms, and 100 atoms of candium. Compare the resulting graphs. 5. Repeat the experiment using half-lives of 5 seconds, 20 seconds, and 1 minute. Compare the resulting graphs. 22

23 Lesson 3A: Introduction to Transmutation Transmutation is defined as This change always turns the unstable element into a more stable element. There are two types of transmutation. Natural Transmutation Begins with one unstable nucleus that spontaneously decays. ****always have ONE REACTANT. Artificial Transmutation is caused by bombarding a These reactions always have Transmutation of one element into another requires a change in the structures of the nuclei of the atoms involved. This results in the release (or gain) of radioactive decay particles How are the particles defined? Alpha, Beta and Gamma can be separated using an electric or magnetic field Positively charged Negatively charged Gamma rays and neutrons 23

24 Lesson 3B: Transmutation - Nuclear Equations Writing Nuclear Equations Nuclear reactions obey laws of The The decay modes can be found on Table N. Alpha Decay: Alpha decay: Example: 238 U undergoes alpha decay U 2 4 He Th The total mass on the left must equal the total mass on the right (238 = ) The total charge on the left must equal the total charge on the right (92 = ) 24

25 Beta decay: Beta (minus) decay: Example: 234 Th undergoes beta decay Th -1 0 e Pa The total mass on the left must equal the total mass on the right (234 = ) The total charge on the left must equal the total charge on the right (90 = ) Positron Emission: Positron (beta plus) decay: Example: 37 K undergoes positron decay K +1 0 e Ar The total of the mass numbers on the left must equal the total on the right (37 = ) The total charge on the left must equal the total charge on the right (19 = ) Gamma Rays: This makes them the most destructive form of nuclear radiation. 25

26 Check your understanding: 1. Complete the example problems below showing alpha decay (remember, CHARGE and MASS must be conserved!) a Fr + He 87 2 b. 222 Rn Complete the example problems below showing beta decay: a P + e 15-1 b C + 3. Complete the example problems showing positron emission: a K + e b. 81 Rb

27 Classwork 12-4:Complete the following decay equations and indicate the type of Decay Type of Decay 1) Cm Pu ) Pu Am ) Am N p ) Np U ) U Th ) Th Pa ) Pa Th

28 8) Th Ra ) Ra Fr ) Fr At More Problems: 11) 12) 13) 14) 15) 16) 17) 18) 19) 28

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30 1. Alpha particles are emitted during the radioactive decay of 1. carbon neon calcium radon Which nuclear reaction is classified as alpha decay? 7. Given the nuclear reaction: Which isotope is represented by the X when the equation is correctly balanced? Given the nuclear reaction: What does X represent in this reaction? 3. Which substance has chemical properties similar to those of radioactive 235 U? Pa 233 Pa 233 U 206 Pb 4. The change that is undergone by an atom of an element made radioactive by bombardment with high-energy protons is called 1. natural transmutation 2. artificial transmutation 3. natural decay 4. radioactive decay 5. Which type of radioactive emission has a positive charge and weak penetrating power? 1. alpha particle 2. beta particle 3. gamma ray 4. neutron 6. Given the reaction: Which type of reaction is represented? Which equation is an example of artificial transmutation? U + 3F 2 UF 6 3. Mg(OH) 2 + 2HCl 2H 2 O + MgCl 2 4. Ca + 2H 2 O Ca(OH) 2 + H In the reaction: the X represents 1. an alpha particle 2. a beta particle 3. an electron 4. a proton 11. Which nuclear equation represents artificial transmutation? 1. natural transmutation 2. artificial transmutation 3. fission 4. fusion 30

31 12. Which particle cannot be accelerated in a magnetic field? 1. alpha particle 2. beta particle 3. neutron 4. proton 13. Given the nuclear equation: What is the identity of particle X in this equation? 14. Given the equation: When the equation is balanced correctly, which particle is represented by X? Bombarding a nucleus with high-energy particles that change it from one element into another is called 1. a half-reaction 2. a breeder reaction 3. artificial transmutation 4. natural transmutation 16. Which process converts an atom from one element to another, when the nucleus of an atom is bombarded with high-energy particles? 1. artificial transmutation 2. natural transmutation 3. addition polymerization 4. condensation polymerization 17. What is the name of the process in which the nucleus of an atom of one element is changed into the nucleus of an atom of a different element? 1. decomposition 2. transmutation 3. substitution 4. reduction 18. Given the reaction: Which particle is represented by X? 1. alpha 2. beta 3. neutron 4. proton 19. Which particle is represented by the letter X? 1. an alpha particle 2. a beta particle 3. a neutron 4. a proton 20. In the equation: the symbol X represents 21. Which type of radiation has neither mass nor charge? 1. gamma 2. neutron 3. alpha 4. beta 22. Which radioisotope is a beta emitter? Sr 220 Fr 37 K 238 U 31

32 23. Which kind of particle, when passed through an electric field, would be attracted to the negative electrode? 1. an alpha particle 2. a beta particle 3. a neutron 4. an electron 24. Which kind of radiation will travel through an electric field on a pathway that remains unaffected by the field? 1. a proton 2. a gamma ray 3. an electron 4. an alpha particle 25. Which equation represents nuclear disentegration resulting in release of a beta particle? 27. Given the nuclear reaction: This reaction is an example of 1. fission 2. fusion 3. artificial transmutation 4. natural transmutation 28. Which type of radiation would be attracted to the positive electrode in an electric field? Which radioactive emanations have a charge of 2+? 1. alpha particles 2. beta particles 3. gamma rays 4. neutrons 26. Which of these types of nuclear radiation has the greatest penetrating power? 1. alpha 2. beta 3. neutron 4. gamma 30. In Rutherford's gold foil experiments, some alpha particles were deflected from their original paths but most passed through the foil with no deflection. Which statement about gold atoms is supported by these experimental observations? 1. Gold atoms consist mostly of empty space. 2. Gold atoms are similar to alpha particles. 3. Alpha particles and gold nuclei have opposite charges. 4. Alpha particles are more dense than gold atoms. 32

33 Lesson 4: Energy and Nuclear Reactions Nuclear fusion and nuclear fission are two different types of energy-releasing reactions in which energy is released from high-powered atomic bonds between the particles within the nucleus. The main difference between these two processes is that fission is the splitting of an atom into two or more smaller ones while fusion is the fusing of two or more smaller atoms into a larger one. Fission Reactions involve the Fission reactions produce/capture neutrons. They can become involved in another fission reaction. 235 U + 1 n 90 Sr Xe n More neutrons are released to keep the reaction going. If the number of neutrons released is not controlled a chain reaction will occur. This is the type of reaction used in nuclear bombs. NOTE: ENERGY is also produced in the above nuclear reaction All nuclear reactors are devices designed to maintain a chain reaction producing a steady flow of neutrons generated by the fission of heavy nuclei. Watch this: 33

34 Fusion Reactions involve 2 H + 3 H 4 He + 1 n In fission and fusion reactions, Hydrogen atoms combine to form helium in a star. The energy of nuclear reactions is much greater than the energy associated with chemical reactions. ENERGY IS PRODUCED AS A PRODUCT IN BOTH FUSION & FISSION REACTIONS! Nuclear reactions produce The energy of One disadvantage of Fission à Disadvantages of Fusion à 34

35 Nuclear Fission Nuclear Fusion Definition: Fission is the splitting of a large atom into two or more smaller ones. Fusion is the fusing of two or more lighter atoms into a larger one. Natural occurrence of the process: Fission reaction does not normally occur in nature. Fusion occurs in stars, such as the sun. Byproducts of the reaction: Fission produces many highly radioactive particles. Few radioactive particles are produced by fusion reaction, but if a fission "trigger" is used, radioactive particles will result from that. Conditions: Critical mass of the substance and high-speed neutrons are required. High density, high temperature environment is required. Energy Requirement: Takes little energy to split two atoms in a fission reaction. Extremely high energy is required to bring two or more protons close enough that nuclear forces overcome their electrostatic repulsion. Energy Released: The energy released by fission is a million times greater than that released in chemical reactions; but lower than the energy released by nuclear fusion. The energy released by fusion is three to four times greater than the energy released by fission. Nuclear weapon: One class of nuclear weapon is a fission bomb, also known as an atomic bomb or atom bomb. One class of nuclear weapon is the hydrogen bomb, which uses a fission reaction to "trigger" a fusion reaction Classwork 12-5:

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41 Optional - Unit Review/Practice Vocabulary Practice: Match each item with the correct statement below. a. positron b. alpha particle c. beta particle d. artificial transmutation e. gamma radiation f. fusion g. fission h. natural transmutation i. radioisotope 1. emitted helium nucleus 2. energetic electron from decomposed neutron 3. high-energy rays (photons) emitted by a radioisotope 4. particle of charge +1 and mass equal to that of an electron 5. conversion of an atom of one element to an atom of another element as a result of natural radioactivity 6. combination of two nuclei to form a nucleus of greater mass 7. splitting of nucleus into smaller fragments 8. Conversion of an atom of one element to an atom of another element resulting from bombarding a nucleus with a high-energy particle, such as a neutron or an alpha particle 9. A bad ratio of neutrons:protons resulting in an unstable nucleus that is radioactive Multiple Choice Identify the number of the choice that best completes the statement or answers the question. 1. An unstable nucleus. (1) increases its nuclear mass by fission (3) emits energy when it decays (2) increases its half-life (4) expels all of its protons 2. The charge on a gamma ray is. (1) +2 (3) 0 (2) 1 (4) 2 3. What particle is emitted in alpha radiation? (1) electron (3) helium nucleus (2) photon (4) hydrogen nucleus 4. A beta particle is a(n). (1) photon (3) helium nucleus (2) electron (4) hydrogen nucleus 5. What is the change in atomic mass when an atom emits a beta particle? (1) decreases by 2 (3) remains the same (2) decreases by 1 (4) increases by 1 6. What is the change in atomic mass when an atom emits gamma radiation? (1) decreases by 2 (3) remains the same (2) decreases by 1 (4) increases by 1 7. The least penetrating form of radiation is. (1) beta radiation (3) alpha radiation (2) gamma radiation (4) positron 41

42 8. Half-reactions can be written to represent all (1) double-replacement reactions (3) fission and fusion reactions (2) neutralization reactions (4) oxidation and reduction reactions 9. Which symbol is used for an alpha particle? (1) He (3) He (2) He (4) He 10. What symbol is used for beta radiation? (1) e (3) e (2) e (4) e 11. Which nuclide is used to investigate human thyroid gland disorders? (1) carbon-14 (3) cobalt-60 (2) potassium-37 (4) iodine When radium-226 (atomic number 88) decays by emitting an alpha particle, it becomes. (1) polonium-222 (3) radium-222 (2) polonium-224 (4) radon What determines the stability of atomic nuclei? (1) the ratio of protons to neutrons (2) the ratio of neutrons to protons (3) the ratio of beta particles to neutrinos (4) the ratio of alpha particles to beta particles 14. What particle is needed to complete this nuclear reaction? Rn Po + (1) He (3) H (2) e (4) n 15. Which reaction converts an atom of one element to an atom of another element? (1) combustion (3) saponification (2) polymerization (4) transmutation 16. What particle is needed to complete the following nuclear equation? Mn + e (1) Co (3) Fe (2) Mn (4) Cr 17. To what element does polonium-208 (atomic number 84) decay when it emits an alpha particle? (1) Pb (3) Pb (2) Po (4) Rn 18. Controlled nuclear chain reactions. (1) take place in nuclear reactors (2) are always fusion reactions (3) never produce radioactive by-products (4) are characteristic of atomic bombs 42

43 19. A reaction in which small nuclei combine to form a heavier nucleus is called. (1) fission (3) background radiation (2) a chemical reaction (4) fusion 20. Nuclear fusion. (1) takes place in the sun (3) can be controlled in the laboratory (2) occurs at low temperatures (4) is used in medicine 21. Which nuclide is listed with its half-life and decay mode? (1) K-37, 1.24 h, α (3) Rn-222, 1.6 x 10 3 y, α (2) N-16, 7.2 s, β - (4) U-235, 7.1 x 10 8 y, β Which nuclear emission has the greatest mass? (1) alpha particle (2) beta particle (3) gamma ray (4) positron 23. Alpha particles are emitted during the radioactive decay of (1) carbon-14 (2) neon-19 (3) calcium-37 (4) radon After 32 days, 5 milligrams of an 80-milligram sample of a radioactive isotope remains unchanged. What is the half-life of this element? (1) 8 days (2) 2 days (3) 16 days (4) 4 days 25. Given the balanced equation representing a nuclear reaction: Which particle is represented by X? (1) (2) (3) (4) 26. The particle represented by X is (1) (2) (3) (4) 27. Which reaction is an example of natural transmutation? (1) (3) (2) (4) 28. Which nuclear equation represents a natural transmutation? (1) (3) (2) (4) 29. In the reaction, what does X represent? (1) a neutron (2) a proton (3) an alpha particle (4) a beta particle 30. Which balanced equation represents a fusion reaction? (1) (3) (2) (4) Short Answer 1. If the half-life of a radioactive material is 8 years, how many years will it take for one half of the original amount of material to decay? 43

44 2. After 42 days, 2 g of phosphorus-32 has decayed to 0.25 g. What is the half-life of phosphorus-32? 3. The radioisotope radon-222 has a half-life of 3.8 days. How much of a 74-g sample of radon-222 would be left after approximately 15.2 days? 4. After how many days is the amount of radon-222 equal to one-sixteenth of its original amount? 5. If the amount of iodine-131 in a sample is 32 g, how much iodine-131 will remain after days? Base your answers to questions 7 and 8 on the information below. A substance known as heavy water can be obtained from ordinary water and could be a significant source of energy in the future. Heavy water contains deuterium, H-2. Instead of the two hydrogen atoms in a typical water molecule, a heavy water molecule has two deuterium atoms. In 3.78 kilograms of ordinary water, the percent composition by mass of heavy water is approximately %. Deuterium atoms completely ionize at approximately 10 8 K. The result is an ionized gas consisting of electrons and deuterons (the nuclei of deuterium). A triton is the nucleus of a tritium atom, H-3. These particles react according to the equations below. In the second equation, X represents an unidentified product. 7.) Calculate the mass of heavy water in a 3.78-kilogram sample of ordinary water. Your response must include both a correct numerical setup and the calculated result. 8.) Identify particle X in the second nuclear equation. Your response must include the symbol, atomic number, and mass number of the particle. 44

45 Base your answers to questions 9 through 11 on the information below. Cobalt-60 is commonly used as a source of radiation for the prevention of food spoilage. Bombarding cobalt-59 nuclei with neutrons produces the nuclide cobalt-60. A food irradiation facility replaces the cobalt-60, a source of gamma rays, when the radioactivity level falls to of its initial level. The nuclide cesium-137 is also a source of radiation for the prevention of food spoilage. 9.) Identify one emission spontaneously released by a cobalt-60 nucleus. 10.) Determine the total number of years that elapse before an original cobalt-60 source in an irradiation facility must be replaced. 11.) Complete the nuclear equation below for the decay of cesium-137. Your response must include the symbol, atomic number, and mass number of the missing particle. Base your answers to questions 12 and 13 on the information below. Scientists are investigating the production of energy using hydrogen-2 nuclei (deuterons) and hydrogen-3 nuclei (tritons). The balanced equation below represents one nuclear reaction between two deuterons. 12.) State, in terms of subatomic particles, how a deuteron differs from a triton. 13.) Identify the type of nuclear reaction represented by the equation. 45

46 Base your answers to questions 14 through 16 on the information below. When a uranium-235 nucleus absorbs a slow-moving neutron, different nuclear reactions may occur. One of these possible reactions is represented by the complete, balanced equation below. For this reaction, the sum of the masses of the products is slightly less than the sum of the masses of the reactants. Another possible reaction of U-235 is represented by the incomplete, balanced equation below. 14.) Identify the type of nuclear reaction represented by equation ) Write a notation for the missing product in equation ) Determine the half-life of krypton-92 if only 6.0 milligrams of an original 96.0-milligram sample remains unchanged after 7.36 seconds. Base your answers to questions 17 and 18 on the information below. The fossilized remains of a plant were found at a construction site. The fossilized remains contain amount of carbon-14 that is present in a living plant. the 17.) Determine the approximate age of these fossilized remains. 18.) Complete the nuclear equation below for the decay of C-14. Your response must include the atomic number, the mass number, and the symbol of the missing particle. 19.) Given the nuclear equation: a.) State the type of nuclear reaction represented by the equation. b.) The sum of the masses of the products is slightly less than the sum of the masses of the reactants. Explain this loss of mass. c.) This process releases greater energy than an ordinary chemical reaction does. Name another type of nuclear reaction that releases greater energy than an ordinary chemical reaction. 46

47 Base your answers to questions 20 through 22 on the reading passage below and on your knowledge of chemistry. A Glow in the Dark, and Scientific Peril The [Marie and Pierre] Curies set out to study radioactivity in Their first accomplishment was to show that radioactivity was a property of atoms themselves. Scientifically, that was the most important of their findings, because it helped other researchers refine their understanding of atomic structure. More famous was their discovery of polonium and radium. Radium was the most radioactive substance the Curies had encountered. Its radioactivity is due to the large size of the atom, which makes the nucleus unstable and prone to decay, usually to radon and then lead, by emitting particles and energy as it seeks a more stable configuration. Marie Curie struggled to purify radium for medical uses, including early radiation treatment for tumors. But radium s bluish glow caught people s fancy, and companies in the United States began mining it and selling it as a novelty: for glow-in-the-dark light pulls, for instance, and bogus cure-all patent medicines that actually killed people. What makes radium so dangerous is that it forms chemical bonds in the same way as calcium, and the body can mistake it for calcium and absorb it into the bones. Then, it can bombard cells with radiation at close range, which may cause bone tumors or bone-marrow damage that can give rise to anemia or leukemia. Denise Grady, The New York Times, October 6, ) State one risk associated with the use of radium. 21.) Using information from the Periodic Table, explain why radium forms chemical bonds in the same way as calcium does. 22.) If a scientist purifies 1.0 gram of radium-226, how many years must pass before only 0.50 gram of the original radium-226 sample remains unchanged? 47

48 Unit Review: Nuclear Chemistry Place a checkmark next to each item that you can do! If a sample problem is given, complete it as evidence. 1. I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit I can still do everything from Unit 11. Type alpha Symbol Mass # Charge Penetrating Power 12. I can compare types of radiation in terms of symbol, mass number, charge, penetrating power, shielding required, and biological hazard. beta gamma neutron positron 48

49 13. I can identify the three types of nuclear reactions. The three types of nuclear reactions are: a. b. c. Definitions: transmutation 14. I can define transmutation, fission, and fusion. fission fusion 15. I can state two synonyms for spontaneous decay. 16. I can show how mass number and electrical charge must be conserved in any nuclear reaction. 17. I can explain what makes a nucleus stable or unstable. Two synonyms for spontaneous decay are: and. Complete the following nuclear equation: The stability of the nucleus is dependent on the to ratio. 18. I can explain the difference between natural transmutation and artificial transmutation. The difference between natural transmutation and artificial transmutation is that in natural transmutation an breaks apart on its own and in artificial transmutation a is made by hitting it with a high energy particle (such as a proton, neutron, or gamma radiation). Which equation represents a natural decay? 19. I can identify a natural decay reaction from a list of reactions. 49

50 Which equation represents artificial transmutation? 20. I can identify an artificial transmutation reaction from a list of reactions. Which equation represents fission? 21. I can identify a fission reaction from a list of reactions. Which equation represents fusion? 22. I can identify a fusion reaction from a list of reactions. 50

51 Which of the following equations represent NUCLEAR reactions? 24. Given a list of reactions, I can differentiate a nuclear reaction from a chemical reaction. 25. I can define half-life. Definition: half-life Based on Reference Table N, what fraction of a radioactive sample of Au-198 will remain unchanged after days? 26. Given the length of the half-life and the amount of time that has passed, I can determine the amount of radioactive sample. What was the original mass of a radioactive sample of K-37 if the sample decayed to 25.0 g after 4.92 seconds? The half-life of K-37 is 1.23 seconds) 27. Given the length of the half-life and the amount of radioactive sample, I can determine the amount of time that has passed. 28. Given the amount of time that has passed and the amount of radioactive sample, I can determine the length of the half-life. 29. Using Table N, I can determine the length of halflife and/or decay mode for a specific radioactive isotope. A g sample of Co-60 decays until only 12.5 g of it remains. Given that the half-life of Co-60 is years, how long did the decay take? What is the half-life of a radioisotope if 25.0 g of an original g sample remains unchanged after days? Compared to K-37, the isotope K-42 has A) shorter half-life and the same decay mode B) shorter half-life and a different decay mode C) longer half-life and the same decay mode D) longer half-life and a different decay mode 51

52 Five beneficial uses for radioactive isotopes are: a. 30. I can state 5 beneficial uses for radioactive isotopes. b. c. d. e. C-14 is used for 31. I can state the scientific use of 4 specific radioactive isotopes. I-131 is used for U-238 is used for Co-60 is used for Three risks associated with radioactivity and radioactive isotopes are: a. 32. I can state three risks associated with radioactivity and radioactive isotopes. b. c. 52

53 Unit 12: Nuclear Chemistry Practice Test 1. Base your answer to the following question on Given the nuclear equation: 1 1H + X 6 3Li + 4 2He The particle represented by X is A) 9 4Li B) 9 4Be C) 10 5Be D) 10 6C 2. Which isotope will spontaneously decay and emit particles with a charge of +2? A) 53 Fe B) 137 Cs C) l98 Au D) 220 Fr 3. Which of these particles has the greatest mass? A) alpha B) beta C) neutron D) positron 4. Base your answer to the following question on Given the nuclear equation: 19 10Ne X F What particle is represented by X? A) alpha B) beta C) neutron D) positron 5. Alpha particles and beta particles differ in A) mass, only B) charge, only C) both mass and charge D) neither mass nor charge 6. Which statement best describes gamma radiation? A) It has a mass of 1 and a charge of 1. B) It has a mass of 0 and a charge of 1. C) It has a mass of 0 and a charge of 0. D) It has a mass of 4 and a charge of Which type of radiation is most similar to high- energy x-rays? A) alpha B) beta C) neutron D) gamma 8. What is the total number of years that must pass before only grams of an original gram sample of C-14 remains unchanged? A) 2865 y B) 5730 y C) y D) y 9. Which isotope is most commonly used in the radioactive dating of the remains of organic materials? A) 14 C B) 16 N C) 32 P D) 37 K 10.Based on Reference Table N, what fraction of a radioactive 90 Sr sample would remain unchanged after 56.2 years? A) B) C) D) 11. What is the half-life and decay mode of Rn-222? A) 1.91 days and alpha decay B) 1.91 days and beta decay C) 3.82 days and alpha decay D) 3.82 days and beta decay 12. After 32 days, 5 milligrams of an 80-milligram sample of a radioactive isotope remains unchanged. What is the half-life of this element? A) 8 days B) 2 days C) 16 days D) 4 days 13. Which reaction converts an atom of one element to an atom of another element? A) combustion B) polymerization C) saponification D) transmutation 14. Radioactive cobalt-60 is used in radiation therapy treatment. Cobalt-60 undergoes beta decay. This type of nuclear reaction is called A) natural transmutation B) artificial transmutation C) nuclear fusion D) nuclear fission 15. In which reaction is mass converted to energy by the process of fission? A) 14 7N + 1 0n 14 6C + 1 1H B) U + 1 0n 87 35Br La n C) Ra Ra + 4 2He D) 2 1H + 2 1H 4 2He 16. Which statement best describes what happens in a fission reaction? 53 A) Heavy nuclei split into lighter nuclei. B) Light nuclei form into heavier nuclei. C) Energy is released and less stable elements are formed. D) Energy is absorbed and more stable elements are formed.