Nuclear Chemistry

Home , Isotopes of tellurium, Positron emission

C H A P T E R

Before nuclear power was used, submarines could stay submerged for only brief periods of time. A diesel-powered sub had to surface regularly to refuel and recharge its batteries. However, 640 with a lump of nuclearCopyright © by Holt, Rine harfuelt and Winston. All rights r eseaboutrved. the size of a golf ball, the ﬁrst nuclear-powered sub could remain underwater for months and travel about 60,000 miles. Today, subs only need to refuel about once every 9 years. Chapter Objectives - Nuclear Chemistry

Review & Atomic Nuclei

Rutherford’s Gold Foil Experiment - Nucleons Nuclide Representation

Nuclear Change

Radioactive Decay Natural/Artiﬁcial Transmutation Nuclear Fission & Fusion Half-Life Nuclear Energy & Waste

Uses of Nuclear Chemistry

Medical, Dating, Power

Chapter Test, Homework, etc. Section 1 – Review & Atomic Nuclei

Rutherford’s Gold Foil Experiment

– determined charge and mass distribution in an atom – 99% of an atom’s mass is in the nucleus, but makes up less than 1% volume – atoms are composed of protons, electrons, and neutrons – protons and neutrons are located in the nucleus of the atom and are called nucleons. – the nucleus has a positive charge.

Nuclear Chemistry

• Concerned with chemistry taking place in the nuclei of atoms • Stability of nuclei depends on the number of protons and neutrons in their nuclei. S E C T I O N Atomic Nuclei 1 and Nuclear Stability

KEY TERMS OBJECTIVES • nucleons 1 Describe how the strong force attracts nucleons. • nuclide 2 Relate binding energy and mass defect. • strong force • mass defect 3 Predict the stability of a nucleus by considering factors such as nuclear size, binding energy, and the ratio of neutrons to protSoEnsC iTn IthOeN nucleus. Atomic Nuclei Nuclear Forces 1 and Nuclear Stability In 1911, Ernest Rutherford’s famous gold-foil experiment determined the TTopicopic LinkLink distribution of charge and mass in an atom. Rutherford’KEYsT EresultsRMS showed OBJECTIVES Refer to the “Atoms and Moles” that all of an atom’s positive charge and almost all of• nucleonsits mass are con-1 Describe how the strong force attracts nucleons. chapter for a discussion of • nuclide tained in an extremely small nucleus. 2 Relate binding energy and mass defect. Rutherford’s experiment. • strong force Other scientists later determined more details about• mass defect the nuclei of3 Predict the stability of a nucleus by considering factors such as nuclear size, binding energy, and the ratio of neutrons to protons in the nucleus. nucleon atoms. Atomic nuclei are composed of protons. The nuclei of all atoms except hydrogen also are composed of neutrons. The number of protons a proton or a neutron Nuclear Forces is the atomic number, Z, and the total number of protons and neutrons isIn 1911, Ernest Rutherford’s famous gold-foil experiment determined the Topic Link the mass number, A.The general symbol for the nucleus of an atom of ele-distribution of charge and mass in an atom. Rutherford’s results showed Refer to the “Atoms and Moles” that all of an atom’s positive charge and almost all of its mass are con- chapter for a discussion of tained in an extremely small nucleus. nuclide ment X is shown in Figure 1. Rutherford’s experiment. Other scientists later determined more details about the nuclei of The protons and neutrons of a nucleus are called nucleons. A nuclide an atom that is identified by the nucleon atoms. Atomic nuclei are composed of protons. The nuclei of all atoms except hydrogen also are composed of neutrons. The number of protons is a general term applied to a specific nucleus with a givena proton number or a neutron of pro- number of protons and neutrons is the atomic number, Z, and the total number of protons and neutrons is in its nucleus tons and neutrons. Nuclides can be represented in two ways. One way,the mass number, A.The general symbol for the nucleus of an atom of ele- nuclide ment X is shown in Figure 1. shown in Figure 1, shows an element’s symbol with its atomic number and The protons and neutrons of a nucleus are called nucleons. A nuclide an atom that is identified by the mass number. A second way is to represent the nuclidenumber by of protons writing and neutrons theis a general term applied to a specific nucleus with a given number of pro- in its nucleus tons and neutrons. Nuclides can be represented in two ways. One way, element’s name followed by itsNuclide mass number Representation, such as radium-228 orshown in Figure 1, shows an element’s symbol with its atomic number and Figure 1 einsteinium-253. It is not essential to include the atomic number whenmass number. A second way is to represent the nuclide by writing the In this figure, X represents Nuclei can be represented in two ways element’s name followed by its mass number, such as radium-228 or • Figure 1 einsteinium-253. It is not essential to include the atomic number when showing a nuclide because all nuclides of an elementIn this have figure, X therepresents same the element, Z represents showing a nuclide because all nuclides of an element have the same The symbol (X) is shown with two numbers on thethe element,top andZ representsbottom the atom’s atomic number, atomic number. the atom’s atomic number, atomic number. and A represents the Recall that isotopesleft ofare it. atoms that have the same atomicand A represents number the but Recall that isotopes are atoms that have the same atomic number but A = Mass number (total # of protons and neutronselement’) s mass number. different mass numbers. So, isotopes are nuclides that have the same num- element’s mass number. different mass numbersZ. So= At,omicisotopes number are (# of nuclides protons) that have the same num-ber of protons but different numbers of neutrons. The following symbols Mass number ber of protons but different numbers of neutrons. The following symbolsrepresent nuclei of isotopes of tellurium. 122Te 124Te 128Te Mass number represent nuclei of isotopes of tellurium. A 52 52 52 These three isotopes of tellurium are stable. So, their nuclei do not break 122 124 128 down spontaneously. Yet, each of these nuclei are composed of 52 pro- 52Te 52Te 52Te tons. How can these positive charges exist so close together? Protons A 70 neutrons 72 neutrons 76 neutrons X repel each other because of their like charges. So, why don’t nuclei fall Z apart? There must be some attraction in the nucleus that is stronger than These three isotopes of tellurium are stable. So, their nuclei doAtomic not number break 52 protons 52 protons 52 protons the repulsion due to the positive charges on protons. down spontaneously. Yet, each of these nuclei are composed of 52 pro- 642 Chapter 18 tons. How can these positive charges exist so close together? Protons Copyright © by Holt, Rinehart and Winston. All rights reserved. X repel each other because of their like charges. So, why don’t nuclei fall Z apart? There must be some attraction in the nucleus that is stronger than Atomic number the repulsion due to the positive charges on protons.

642 Chapter 18

The element name is given followed by the Mass Number

Radium-228 or Ra-228

Nuclei that have mass numbers greater than 209 and atomic numbers greater than 83 are never stable. Section 2 – Objectives

Radioactive Decay

Stabilizing unstable nuclei Nuclear particle and ray emission (α, β, positrons, ϒ-rays) Balancing nuclear equations Natural & Artiﬁcial Transmutation Nuclear Fission & Fusion What takes place? Chain Reactions in Nuclear Reactors Half-Life

Nuclear Energy and Waste Section 2 – Nuclear Change

Radioactive Decay - Only a few types of nuclear changes occur.

Radioactivity - the process by which an unstable nucleus emits one or more particles and energy in the form of electromagnetic energy to make a more stable nucleus. Table O Symbols Used in Nuclear Chemistry

Name Notation Symbol

4 4 alpha particle 2He or 2! ! 0 0 – beta particle (electron) –1e or –1 " " 0 gamma radiation 0# # 1 neutron 0n n 1 1 proton 1H or 1p p 0 0 + positron +1e or +1 " "

Table P Organic Prefixes

Prefix Number of Carbon Atoms meth- 1 eth- 2 prop- 3 but- 4 pent- 5 hex- 6 hept- 7 oct- 8 non- 9 dec- 10

Table Q Homologous Series of Hydrocarbons

Examples Name General Formula Name Structural Formula H H

alkanes CnH2n+2 ethane H C C H H H H H alkenes CnH2n ethene C C H H

alkynes CnH2n–2 ethyne H C C H n = number of carbon atoms 6 Reference Tables for Physical Setting/CHEMISTRY Figure 7 When the unstable carbon-14 nucleus emits beta decay – a beta particle, the + carbon-14 nucleus changes into a nitrogen-14 nucleus.

14 14 beta particle 6 C → 7 N + 0 −1e

BecauseBecause this the procprocessess changes changes a neutr a neutronon into ainto prot aon proton,, the atomicthe atomic numbernumber of the of nucleus the nucleus increases increases by by one one., as you can see in Figure 7. As a Figure 8 result of beta decay, carbon becomes a different element, nitrogen. Thunderstorms may produce Figure 7 terrestrial gamma-ray When the unstable However, the mass number does not change because the total numbercarbon-14 of nucleus emitsflashes (TGFs). beta decay – a beta particle, the nucleons does not change as shown by the following equation.+ carbon-14 nucleus changes into a 14 14 0 nitrogen-14 nucleus. 6C → 7N + −1e

14 14 beta particle C → N + 6 7 0e Stabilizing Nuclei by Converting Protons into Neu−1 trons One way that a nucleus that has too many protons can become more stable is by a processStabilizin gcalled Nuclei belectrony Converti ncaptureg Neutron.s Inint o thisProt oprocessns , the nucleus merely absorbsRec aonell tha t ofthe sthetabil itatom’y of a nusc lelectronseus depends o,nusually the ratio o ffrom neutro nthes beta1s parorbital.ticle to protons, or the N/Z number. If a particular isotope has a large N/Z a charged electron emitted This process numberchanges or too a many proton neutrons into, the nucleus a neutron will decay andand emit decreases radiation. theduring atomic a certain type of A neutron in an unstable nucleus may emit a high-energy electron, radioactive decay, such as beta decay number by onecalled. T ahe beta mass particle number(␤ particle), staysand change the to same a proton.. This process is called beta decay. This process often occurs in unstable nuclei that have gamma ray electron capture large N/Z numbers1 . 0 1 the high-energy photon emitted +1p + −1e → 0n 1 beta decay 1 0 by a nucleus during fisson and 0n → +1p + −1e radioactive decay A typical nucleusBecause that this decays process changesby this a neutronprocess into is a proton,chromium-51.the atomic number of the nucleus increases by one, as you can see in Figure 7. As a Figure 8 result of 51beta decay,0carbonelectron becomes capture a different51 element, nitrogen. Thunderstorms may produce 24Cr + −1e → 23V + ␥ terrestrial gamma-ray However, the mass number does not change because the total number of flashes (TGFs). nucleons does not change as shown by the following equation. The final symbol in the equation,14 ␥, 14indicates0 the release of gamma rays. 6C → 7N + −1e Many nuclear changes leave a nucleus in an energetic or excited state. When the nuSctalbeiulizsi nsgt Naubcilleiiz beys C, ointv erretilnega Psreosto nesn ientrog Nye uintr otnhs e form of gamma Figure 8One way that a nucleus that has too many protons can become more sta- rays. blesh iso byw sa aprocess thu ncalledder electronstorm capture duri.nIng this w hprocessich g, athem nucleusma rays may also be produced.merely absorbs one of the atom’s electrons, usually from the 1s orbital. This process changes a proton into a neutron and decreases the atomic number by one. The mass number stays the same. Nuclear Chemistry 649 1 0 electron capture 1 +1p + −1e → 0n Copyright © by Holt, Rinehart and Winston. All rights reserved. A typical nucleus that decays by this process is chromium-51.

51 0 electron capture 51 24Cr + −1e → 23V + ␥

The final symbol in the equation, ␥, indicates the release of gamma rays. Many nuclear changes leave a nucleus in an energetic or excited state. When the nucleus stabilizes, it releases energy in the form of gamma rays. Figure 8 shows a thunderstorm during which gamma rays may also be produced.

Nuclear Chemistry 649

Copyright © by Holt, Rinehart and Winston. All rights reserved. Figure 7 When the unstable carbon-14 nucleus emits beta decay – a beta particle, the + carbon-14 nucleus changes into a nitrogen-14 nucleus.

14 14 beta particle 6 C → 7 N + 0 −1e

Stabilizing Nuclei by Converting Neutrons into Protons Recall that the stability of a nucleus depends on the ratio of neutrons beta particle to protons, or the N/Z number. If a particular isotope has a large N/Z a charged electron emitted number or too many neutrons, the nucleus will decay and emit radiation. during a certain type of A neutron in an unstable nucleus may emit a high-energy electron, radioactive decay, such as beta decay called a beta particle (␤ particle), and change to a proton. This process is called beta decay. This process often occurs in unstable nuclei that have gamma ray large N/Z numbers. the high-energy photon emitted 1 beta decay 1 0 by a nucleus during fisson and 0n → +1p + −1e radioactive decay Because this process changes a neutron into a proton, the atomic number of the nucleus increases by one, as you can see in Figure 7. As a Figure 8 result of beta decay, carbon becomes a different element, nitrogen. Thunderstorms may produce terrestrial gamma-ray However, the mass number does not change because the total numberFigure 7 of When the unstable flashes (TGFs). carbon-14 nucleus emits beta decay – a beta particle, the nucleons does not change as shown by the following equation.+ carbon-14 nucleus changes into a nitrogen-14 nucleus. 14C 14N 0e 6 → 7 +14 −1 14 beta particle 6 C → 7 N + 0 −1e Electron Capture - Gamma Radiation Stabilizing Nuclei by Converting Neutrons into Protons Recall that the stability of a nucleus depends on the ratio of neutrons beta particle to protons, or the N/Z number. If a particular isotope has a large N/Z a charged electron emitted Stabilizing Nuclei by Converting numberPr oro toot manyo nneutronss , ithen nucleusto will Ndecaye andu emitt radiation.ronsduring a certain type of A neutron in an unstable nucleus may emit a high-energy electron, radioactive decay, such as beta decay called a beta particle (␤ particle), and change to a proton. This process is One way that a nucleusIf a nucleus that has hastoo many too manyprotcalled betaons, deca protonsy. Tithis processmay often capture occurs can in unstable become an nuclei electron that have moregamma f romray sta- the large N/Z numbers. the high-energy photon emitted by a nucleus during fisson and atom. 1 beta decay 1 0 ble is by a process called electron capture. In0n this→ +1p +process−1e , theradioactive nucleus decay Because this process changes a neutron into a proton, the atomic number of the nucleus increases by one, as you can see in Figure 7. As a Figure 8 merely absorbs one of the atom’s electronsresult of beta decay, , usuallycarbon becomes a differentfrom element, thenitrogen. 1Tshunderstormsorbital. may produce This process changes a proton into a neutron and decreasesterrestrial the gamma-ray However, the mass number does not change because the total number of flashes (TGFs). This process changesatomic numbera proton by one.into The anucleons neutronma doesss not number change asand shown bystays the decreases following the equation. same . the atomic 14 14 0 6C → 7N + −1e number by one. The mass number staysStabi lithezing Nuc lesamei by Convert.ing Protons into Neutrons One way that a nucleus that has too many protons can become more stable is by a process called electron capture. In this process, the nucleus 1 0 electronmerely absorbscapture one of the atom’1s electrons, usually from the 1s orbital. This process changes a proton into a neutronϒ and decreases the atomic +1p + −1e number by one. The mass→ number0n stays the+ same.

1 0 electron capture 1 +1p + −1e → 0n

A typical nucleus that decays by this process is chromium-51.

A typical nucleus that decays by this process51 is 0 chromium-51.electron capture 51 24Cr + −1e → 23V + ␥

The final symbol in the equation, ␥, indicates the release of gamma rays. electronMany capture nuclear changes leave a nucleus in an energetic or excited state. ϒ = gamma51 rays 0 When the nucleus stabi51lizes, it releases energy in the form of gamma 24Cr + −1e rays. Figure 8 sh→ows a th23undeVrstorm +duri ng␥ which gamma rays may also be produced. When the nucleus stabilizes, it releases energy in the form of gammaNuclear Chemistry 649 Copyright © by Holt, Rinehart and Winston. All rights reserved. The final symbolrays. in the equation, ␥, indicates the release of gamma rays. Many nuclear changes leave a nucleus in an energetic or excited state. When the nucleus stabilizes, it releases energy in the form of gamma rays. Figure 8 shows a thunderstorm during which gamma rays may also be produced.

Nuclear Chemistry 649

Copyright © by Holt, Rinehart and Winston. All rights reserved. Figure 9 Nuclei can release positrons to form new nuclei. Matter is + then converted into energy when positrons and electrons collide and are converted into gamma rays. positron 49 49 0 24Cr → 23 V + +1e

+ 2␥

positron electron energy in the form of 0 + 0 +1e −1e → gamma rays

Gamma Rays Are APlsoositron Emitted i nEmission Positron Emission Some nucleiSome nuclei that have that hatoove manytoo many protons protons can an become become stable stable byby emitting positronspositrons, which = are the the antipar antiparticlesticles of electrons. of electrons.The process is similar to electron capture in that a proton is changed into a neutron. However, in positron emission, a proton emits a positron.

1 positron emission 1 0 +1p → 0n + +1e Notice that when a proton changes into a neutron by emitting a positron, Topic Link the mass number stays the same, but the atomic number decreases by one. Figure 9 ReNfeur ctloe it hcea n“ Arteolmeass ea npdo sMitorolenss” The isotope chromium-49 decays by this process, as shown by the model to chapterform ne wfor n au cdiscussionlei. Matte rof is in Figure 9. electromagnetic waves. + then converted into energy 49 49 0 24Cr → 23V + +1e when positrons and electrons collide and are converted Another example of an unstable nucleus that emits a positron is potas- into gamma rays. sium-38, which changes into argon-38. positron 49 49 + 0 24Cr →38 38 023 V +1e 19K → 18Ar + +1e The positron is the opposite of an electron. Unlike a beta particle, a positron seldom makes it into the surroundings. Instead, the positron usually collides with+ an electron, its antiparticle. Any time a particle collides2␥ with its antiparticle, all of the masses of the two particles are converted entirely into electromagnetic energy or gamma rays. This process is called annihilationpositron of matterelect, whichron is illustrated in Figure 9. energy in the form of 0 + 0 annihilation +1e −1e 0 0 → gamma rays −1e + +1e → 2␥ The gamma rays from electron-positron annihilation have a characteristic wavelength; therefore, these rays can be used to identify nuclei that decay byGa positronmma R aemission.ys Are ASuchlso gammaEmitte drays in havePosi tbeenron detectedEmissio ncoming from theSome center nuclei of thethat Milky have Wtooay manygalaxy protons. can become stable by emitting positrons, which are the antiparticles of electrons.The process is similar to 650 Chapter 18 electron capture in that a proton is changed into a neutron. However, in positron emission, a proton emits a positron.Copyright © by Holt, Rinehart and Winston. All rights reserved.

38 38 0 19K → 18Ar + +1e The positron is the opposite of an electron. Unlike a beta particle, a positron seldom makes it into the surroundings. Instead, the positron usually collides with an electron, its antiparticle. Any time a particle collides with its antiparticle, all of the masses of the two particles are converted entirely into electromagnetic energy or gamma rays. This process is called annihilation of matter, which is illustrated in Figure 9.

0 0 annihilation −1e + +1e → 2␥ The gamma rays from electron-positron annihilation have a characteristic wavelength; therefore, these rays can be used to identify nuclei that decay by positron emission. Such gamma rays have been detected coming from the center of the Milky Way galaxy.

650 Chapter 18

S E C T I O N KEY TERMS OBJECTIVES • radioactivity 1 Predict the particles and electromagnetic waves produced by • beta particle different types of radioactive decay, and write equations for nuclear decays. • gamma2 ray Nuclear Change • nuclear fission 2 Identify examples of nuclear fission, and describe potential benefits and hazards of its use. • chain reaction • critical mass 3 Describe nuclear fusion and its potential as an energy source. KEY TERMS OBJECTIVES • nuclear fusion • radioactivity 1 Predict the particles and electromagnetic waves produced by • beta particle Raddifferentioact itypesve D ofe radioactivecay decay, and write equations for nuclear decays. • gamma ray Nuclear changes can be easier to understand than chemical changes • nuclear fission 2becaIdentifyuse onlyexamples a few ty pofe snuclear of nucl efission,ar cha nandges describeoccur. O npotentiale type is benefits the spon- and hazards of its use. • chain reaction taneous change of an unstable nucleus to form a more stable one. This change involves the release of particles, electromagnetic waves, or both • critical mass 3 Describe nuclear fusion and its potential as an energy source. radioactivity and is generally called radioactivity or radioactive decay. Specifically, • nuclear fusion the process by which an unstable radioactivity is the spontaneous breakdown of unstable nuclei to produce nucleus emits one or more parti- particles or energy. Table 1 summarizes the properties of both the particles cles or energy in the form of Ranadd thioe aencetrigvy ere lDeaesecda byy radioactive decay. electromagnetic radiation Nuclear changes can be easier to understand than chemical changes because only a few types of nuclear changes occur. One type is the spon- Table 1 Characteristics of Nuclear Particles and Rays taneous change of an unstable nucleus to form a more stable one. This cAlphahPaarticlenge involv ePs thMassare r e(amu)ticlelease of p aChargeEmissionrticles, eSlymbolectromagneticStopped waves by, or both radioactivity and is generally called radioactivity or rad+ioa1cti1ve decay. Specifically, Proton 1.007 276 47 +1 p, p , +1p, 1H a few sheets the process by which an unstable radioactivity is the spontaneous breakdown of unstable nuofc lpaperei to produce nucleus emits one or more parti- particles or energy. Table 1 summarizes the properties of both the particles n n0 1n cles or energy in the Uformnstable of nucleianNeutrond th cane en edecayrgy rel1.008 ebyase emittingd664 by 90 radio aan0cti valphae deca, y(.α, 0) particlea few centi- meters of lead electromagneticwww.sciStlinks.orga radiationbilizing Nuclei by Losing Alpha Particles Topic: Radioactive Decay − 0 ␤ particle 0.000 548 580 −1 ␤, ␤ , − e* a few sheets of SciLinks code:AnHW4106 unstable nucleus that has an N/Z number that 1is much larger than 1 (electron)Table 1 Characteristics of Nuclear Particles and aluminumRays foil

can decay by emitting an alpha particle. In addition,+ 0 none of the elements PParticleositron† Mass0.000 (amu) 548 580 +Charge1 ␤Symbol, +1e* sameStopped as byelectron that have atomic numbers greater than 83 and mass2+ 4numbers greater than ␣ particle 4.001 474 92 +2 ␣, ␣+ , 12He1 skin or one Proton 1.007 276 47 +1 p, p , +1p, 1H a few sheets 209 have stable (He-4isotopes nucleus). So, many of these unstable isotopessheetof paper of paperdecay by emitting alpha particlesGamma ray , as 0well as by electron0 ␥ 0capture1 orseveral beta centi- decay. Neutron 1.008 664 90 0 n, n , 0 n a few centi- Topic Link Atomic number decreases by two and mass number decreametersmetersses by ofof 4. leadlead www.sciUranium-238links.org is one example. Topic: Radioactive EmissionsDecay − 0 Refer to the “Atoms and ␤ particle 0.000 548 580 −1 ␤, ␤ , −1e* a few sheets of SciLinks code: HW4106HW4107 *The superscript zero in the symbols for electron and positron does not mean (electron)238 alpha decay 234 4 aluminum foil Moles” chapter for a that they92 haveU zero mass. It means→ their90 massTh +number 2He is zero. discussion of alpha particles. Positron† 0.000 548 580 +1 ␤+, 0e* same as electron †The positron is the antiparticle of the electron. Each+1 particle has an antiparticle, Notice that the atomicbut only thenumber positron is in frequently the equation involved in decreasesnuclear2+ 4 changes by. two while the Many heavy ␣metalsparticle (like U4.001ranium 474 92-238) go+2 through␣, ␣ ,a2H seriese ofskin reactions or one mass number decreases(He-4 nucleus) by four. Alpha particles have verysheet low of penetrat-paper 648 Chapter 1cal8 led a decay series. ing ability becauseGamma they ray are0 large and 0soon collide␥ with severalother centi- matter. Copyright © by Holt, Rinehart and Wmetersinston. A llof rig hleadts reserved. www.sciExposurelinks.org to external sources of alpha radiation is usually harmless. Topic: Radioactive Emissions SciLinks code:HoweverHW4107 , if substances*The superscript that zeroundergo in the symbols alpha for electrondecay and are positron ingested does not or mean inhaled, the radiation canthat be they quite have zerodamaging mass. It means to theirthe mass body’ numbers internal is zero. organs. †The positron is the antiparticle of the electron. Each particle has an antiparticle, Many heavybut n uonlycle thei gpositrono thr iso frequentlyugh a sinvolvederies ino fnuclear reac changestions. called a decay series before they reach a stable state.The decay series for uranium-238 is 648 Chapter 18 238 234 shown in Figure 10. After the 92U nucleus decays to 90Th, the nucleus is still unstable because it has a large N/Z numCobpyreighrt ©. bTy Hholti, Rsin enhaurt acndl Weinustosn. Aull rnighdts reesrergvedo. es 234 234 beta decay to produce 91Pa. By another beta decay, 91Pa changes 234 to 92U. After a number of other decays (taking millions of years), the 206 nucleus finally becomes a stable isotope, 82Pb. Figure 10 Uranium-238 decays to lead-206 through a decay Uranium-238 Decay Series series.

242

238 238 92 U 4.5 X 109 y

234 234 234 234 90 Th 91Pa 92U 24.1 d 1.2 min 2.5 X 105 y

230 230 90 Th 7.5 X 104 y

226 226 88Ra 1599 y

222 222 86Rn 3.8 d

Mass number 218 218 218 84 Po 85 At 3.0 min 1.6 s

214 214 214 214 82Pb 83Bi 84 Po 27. min 19.9 min 163.7 µs

210 210 210 210 s = seconds 210 81 Tl 82Pb 83 Bi 84 Po min = minutes 1.3 min 22.6 y 5.01 d 138.4 d d = days 206 206 y = years 206 81 Tl 82Pb = alpha decay 4.2 min stable = beta decay

202 80 81 82 83 84 85 86 87 88 89 90 91 92 93 Atomic number

Nuclear Chemistry 651

α-decay

β-decay β-decay Table K Table N Common Acids Selected Radioisotopes

Formula Name Nuclide Half-Life Decay Nuclide Spontaneous/Natural Mode Name HCl(aq) hydrochloric acid 198Au 2.69 d !– gold-198 HNO3(aq) nitric acid Transmutation 14C 5730 y !– carbon-14 H2SO4(aq) sulfuric acid 37Ca 175 ms !+ calcium-37 H3PO4(aq) phosphoric acid 60Co 5.26 y !– cobalt-60 Decay reactions that do not require an outside H2CO3(aq) or carbonic acid 137Cs 30.23 y !– cesium-137 energy source to proceed are considered CO (aq) 2 53Fe 8.51 min !+ iron-53 CH COOH(aq) spontaneous and natural. 3 ethanoic acid 220Fr 27.5 s " francium-220 or (acetic acid) 3 – HC2H3O2(aq) H 12.26 y ! hydrogen-3 • One atom on the left hand side of the 131I 8.07 d !– iodine-131 reaction 37K 1.23 s !+ potassium-37 Table L 42K 12.4 h !– potassium-42 • Forms multiple particles Common Bases 85Kr 10.76 y !– krypton-85 16 – Formula Name N 7.2 s ! nitrogen-16 19 + NaOH(aq) sodium hydroxide Ne 17.2 s ! neon-19 32 – KOH(aq) potassium hydroxide P 14.3 d ! phosphorus-32 239Pu 2.44 ! 104 y " plutonium-239 Ca(OH)2(aq) calcium hydroxide Artiﬁcial Transmutation 226Ra 1600 y " radium-226 NH3(aq) aqueous ammonia 222Rn 3.82 d " radon-222 Decay reactions that need an external energy 90Sr 28.1 y !– strontium-90 99Tc 2.13 ! 105 y !– technetium-99 source to proceed are considered artiﬁcial. Table M Common Acid–Base Indicators 232Th 1.4 !"1010 y " thorium-232 • Multiple atom/particle on the left hand side 233U 1.62 ! 105 y " uranium-233 Approximate 235 8 of the reaction Indicator pH Range Color U 7.1 ! 10 y " uranium-235 for Color Change 238U 4.51 ! 109 y " uranium-238 Change • Forms multiple particles or a single product ms = milliseconds; s = seconds; min = minutes; methyl orange 3.2–4.4 red to yellow h = hours; d = days; y = years bromthymol blue 6.0–7.6 yellow to blue phenolphthalein 8.2–10 colorless to pink litmus 5.5–8.2 red to blue bromcresol green 3.8–5.4 yellow to blue thymol blue 8.0–9.6 yellow to blue

Reference Tables for Physical Setting/CHEMISTRY 5 Figure 7 When the unstable carbon-14 nucleus emits beta decay – a beta particle, the + carbon-14 nucleus changes into a nitrogen-14 nucleus.

14 14 beta particle 6 C → 7 N + 0 −1e

Stabilizing Nuclei by Converting Neutrons into Protons Figure 7 When the unstable Recall that the stability of a nucleus depends on the ratio of neutrons betacarbon-14 particle nucleus emits Figure 9 to protons, or the N/Z numberbeta decay. If a particular isotope has a large N/Z– a chargeda beta particle electron, theemitted Nuclei can release positrons + carbon-14 nucleus to form new nuclei. Matternumber is or too many neutrons, the nucleus will decay and emit radiation. during a certain type of + changes into a then converted into energy radioactive decay, such as A neutron in an unstable nucleus may emit a high-energy electron, nitrogen-14 nucleus. when positrons and electrons beta decay collide and are converted called a beta particle (␤ particle), and change to a proton. This process is into gamma rays. called beta decay. This process often occurs in unstable nucleipositron that have gamma ray 49Cr → 49 V + 0e large N/Z numbers24 . 23 +beta1 particle the high-energy photon emitted 14 C 14 N 6 → 7 + 0 by a nucleus during fisson and 1 beta decay 1 0 −1e 0n → +1p + −1e radioactive decay Because this process changes a neutron into a proton, the atomic + 2␥ numberStabi lofiz itheng Nnucleusuclei b increasesy Conver bytin gone N,easut ryouons canint osee Pr inot oFigurens 7. As a Figure 8 result of beta decay, carbon becomes a different element, nitrogen. Thunderstorms may produce Recall that the stability of a nucleus depends on the ratio of neutrons betaterrestrial particle gamma-ray Howeverpositron, the mass numberelectron does not change because the totalenergy number in of to protons, or the N/Z number. If a particular isotope hasthe a form large of N/Z a chargedflashes electron (TGFs). emitted 0e + 0e → nucleonsnumber +does1 or too not many change −neutrons1 as shown, the nucleusby the followingwill decay equation.and emitgamma radiation. rays during a certain type of A neutron in an unstable nucleus may emit a high-energy electron, radioactive decay, such as 14C 14N 0e beta decay called a betaR paradioactivticle (␤ particle),6 e →Decaand7 change+y− 1Summar to a proton.yThis process is calledGam betama Rdecaaysy A. Trehis A lprocessso Emi toftented in occurs Positr inon unstableEmissio nnuclei that have gamma ray large N/Z numbers. StabiSomelizin nucleig NuBeta cthatle iDecay haveby C too- oneutronsn manyvert iprotonstno gprot Ponsr ocanto becomens into stable Neu bytr oemittingns the high-energy photon emitted positrons, which are the antiparticles1 beta decay of electrons1 0.The process is similar to by a nucleus during fisson and One way that a nucleus that0n has too →many+1p protons+ −1e can become more sta- radioactive decay electron capture in that a proton is changed into a neutron. However, in ble is by a process called electron capture. In this process, the nucleus positronBecause emission, thisPositron processa protonEmission changes emits - prot a onspositron.a neutron to neutrons into a proton, the atomic merely absorbs one of the atom’s electrons, usually from the 1s orbital. positron emission Figure 8 numberStabil iofzi ntheg N nucleusuclei b yincreases1 pLosing Abylp oneha ,Pasa1nr tyouicl0e ecans see in Figure 7. As a This process changes a proton+1  into a neutron→ 0 + + 1and decreases the atomic Thunderstorms may produce resultAn unstableof beta nucleus decay, thatcarbon has anbecomes N/Z number a different that is much element, largernitrogen. than 1 numberNotice by thatone .whenThe amass proton number changes stays into a the neutron same by. emitting a positron, terrestrial gamma-ray Howevercan decay, the by Electronmass emitting number C anapture alpha does - prot particle notons changeto. Inneutrons addition, becausenone the of total the elementsnumber of flashes (TGFs). Topic Link the mass number stays the same, but the atomic number decreases by one. nucleonsthat have does atomic not numberschange1 as greater 0shownelectron than by 83the capture and following mass1 numbers equation. greater than p + e → n Refer to the “Atoms and Moles” 209The have isotope stable chromium-49 isotopes+1 . Sodecays−1, many by ofthis these process unstable, as0 shown isotopes by the decay model by chapter for a discussion of in Figure 9. 14 14 0 electromagnetic waves. emitting alpha particles, as 6wellC → as 7byN +electron−1e capture or beta decay. A typical nucleusAlpha that Par decaysticle Emission49 by this - 49loss process of a0 H eliumis chromium-51. nucleus Topic Link Uranium-238 is one example24.Cr → 23V + +1e Refer to the “Atoms and 51 0 electron capture 51 Another example of 238an unstablealpha decaynucleus234 that emits4 a positron is potas- Moles” chapter for a Stabilizing Nucl24eiCr by + UC−o 1enverting→ ProTt→ohn +23s ViHen t+o ␥ Neutrons sium-38, which changes92 into argon-38. 90 2 discussion of alpha particles. One way that a nucleus that has too many protons can become more sta- The finalNotice symbol that the in atomic the equation, number38 in ␥the,38indicates equation0 thedecreases release by oftwogamma while the rays. ble is by a process called electron19K → 18 captureAr + +1e. In this process, the nucleus Manymass nuclear number changes decreases leave by four a nucleus. Alpha particlesin an energetic have very orlow excited penetrat- state. merely absorbs one of the atom’s electrons, usually from the 1s orbital. WheingnT het hability epositron nuc becausele uiss thesta theyboppositeiliz eares, i largetof r eanl e andaelectron.se ssoon ene rUnlikecollidegy in awitht hbetae fothero rparticlem omatterf ,gaam. ma ThisExposurepositron process seldom to changes external makes a protonitsources into the intoof surroundings alpha a neutron radiation. Instead, and isdecreases theusually positron harmlessthe usu- atomic. rays. Figure 8 shows a thunderstorm during which gamma rays may also numberHoweverally collides by, oneif substanceswith. The an mass electron, that number undergoits antiparticle stays alpha the decay. Anysame timeare. ingested a particle or collides inhaled, be prtheod uradiationced. can be quite damaging to the body’s internal organs. with its antiparticle, all1 of the0 masseselectron of capturethe two 1particles are converted entirelyMan yinto he aelectromagneticvy nucle+i1 pgo+ t−h energy1reough ora sgammaeries o→ raysf r0en.aTchistion processs called is acalled decay Nuclear Chemistry 649 sannihilationeries before ofth emattery reac, hwhich a sta bisl eillustrated state.The in d eFigurecay se 9.ries for uranium-238 is A typical nucleus that decays 2by38 this process is chromium-51.234 Copyrighst h©obyw Hnol t,i nRi nFeihgarut arned 1W0in.stAon.f tAell rr igthhtse r ese9r2vUed.annihilation nucleus decays to 90Th, the nucleus is 0e + 0e → 2␥ still unstable becau51se it h−1as0 a +l1electronarge N/ Zcapturenumbe51r. This nucleus undergoes 24Cr + 2−314e → 23V + ␥ 234 bTeheta gammadecay trayso p fromrodu celectron-positrone 91Pa. By ano annihilationther beta d haveecay ,a characteristic91Pa changes 234 Thetwavelength;o final92U .symbolAftethereforer a in n uthem,b theseeequation,r of raysoth ecanr␥ ,d indicatesebeca usedys (t atok the iidentifyng releasemill inucleions of of that gammayea decayrs), traheys. 206 Manynbyuc lpositron enuclearus fina lemission.l ychanges becomeSuch sleave a s tgammaa bale nucleus iso raystope have, in82 Pan beenb. energetic detected or coming excited from state. Figure 10 Whtheen centerthe n uofc ltheeu sMilky stab iWlizayes galaxy, it re.leases energy in the form of gamma Uranium-238 decays to lead-206 through a decay rays. Figure 8 shows a thunderstorm during which gamma rays may also 650 Chapter 18 Uranium-238 Decay Series series. be produced. Copyright © by Holt, Rinehart and Winston. All rights reserved. 242 Nuclear Chemistry 649 238 Copyright2 ©38by Holt, Rinehart and Winston. All rights reserved. 92 U 4.5 X 109 y

234 234 234 234 90 Th 91Pa 92U 24.1 d 1.2 min 2.5 X 105 y

230 230 90 Th 7.5 X 104 y

226 226 88Ra 1599 y

222 222 86Rn 3.8 d

Mass number 218 218 218 84 Po 85 At 3.0 min 1.6 s

214 214 214 214 82Pb 83Bi 84 Po 27. min 19.9 min 163.7 µs

210 210 210 210 s = seconds 210 81 Tl 82Pb 83 Bi 84 Po min = minutes 1.3 min 22.6 y 5.01 d 138.4 d d = days 206 206 y = years 206 81 Tl 82Pb = alpha decay 4.2 min stable = beta decay

202 80 81 82 83 84 85 86 87 88 89 90 91 92 93 Atomic number

Nuclear Chemistry 651

PART A For each item, write on a separate piece of paper the number of the word, expression, or statement that best answers the item.

1. In Rutherford’s gold foil experiment some 6. Which ratio is used to predict the stability of the positively charged alpha particles of an isotope? were deflected back from the gold foil. As a (1) protons to electrons result of this experiment, he concluded that (2) neutrons to protons the nucleus of an atom occupied a (3) neutrons to electrons (1) large part of an atom and had a positive (4) neutrons to nucleons charge. 7. What is the neutron to proton ratio for (2) small part of an atom and had a positive an atom of lead-205? charge. (1) 1:2 (3) large part of an atom and had a negative PART B–1 (2) 2:1 10. A nucleuscharge .of helium-4 weighs 0.0304 amu 17. Which describes a positron? For each item, write on a separate piece of paper the number(3) 1: of1.5 the word, expression, or less(4) small than thepart sum of an of atomthe masses and had of aits negative pro- (1) same mass and charge as an electron statement that best answers the item. (4) 1.5:1 tonscharge and neutrons. . This mass defect can best (2) mass of a proton and a +1 charge be explained by 8. (3)In small,mass ofstable an electron atoms the and nucleus a +1 charge usually 2. Which particles are classified as nucleons? 23. T(1)hethe nucleus conversion of the of nuclide mass to protactinium-231 nuclear bind- 30.(4)containsheaviestIdentify subatomica product particleof the radioactive decay (1) protons and electrons containsing energy. (1) ofneutrons cesium-137. to protons in a 1 to 1 ratio. (2) neutrons and electrons 18. Which isotope is most likely to be used as a (1)(2)91a contradiction protons and to 140 the neutrons law of conserva-. (2) (1)protonspositron to neutrons in a 1.5 to 1 ratio. (3) protons and neutrons fuel for a fission reaction? (2) 91tion protons of mass and. 140Section electrons. Review (3) (2)neutronscesium-136 to protons in a 1.5 to 1 ratio. (4) protons, neutrons, and electrons (1) oxygen-18 (3)(3)91miscalculation neutrons and of the140 massprotons of a. proton. (4) (3) beta particle (2) hydrogen-3neutrons to protons in a greater than 1.5 (4) miscalculation of the mass of a neutron. 3.(4)Which91 neutrons symbol represents and 140 electrons a nuclide. with 16 (3) calcium-(4)to 1alpha ratio41. particle protons and 18 neutrons? 24.11.HowWhich many Group nucleons 16 element are haspresent no stable in an atom 9.31.(4)Whichuranium-235Examine combination the following of proton nuclear number equation. and isotope?(1) 34Se (3) 34S neutron number yields a nucleus that is least of thorium-232?16 16 19. What is the major131 obstacle131 to fusing two (1) O (3) Te 53I → 54Xe + A (1) 32316 (3)18232 nucleistable? to form a single nucleus? (2)(2) S18Se (4)(4) P16oS (2) 90 (4) 142 (1)(1) smallWeven/evenhat size particle of the is nuclei represented by A? 4. Protons and neutrons are made up of (2) even/odd 12. Which radioactive emission has a charge of (2) small(1) proton mass of the nuclei (3) alpha particle 25. Compared(1) electrons to. a carbon-12(3) nucleons nucleus., a (3) odd/even +2 and a mass of 4 amu? (3) repulsion(2) neutron of the nuclei (4) beta particle carbon-14(1)(2) alphapositrons particle nucleus. has(3)(4) twopositronquarks . (4)(4) numberodd/odd of neutrons in the nuclei (1) fewer protons. (3) more neutrons. 32. What does X represent in the following 5. (2)Samplesbeta particle of elements that(4) gammaare radioactive ray (2) more protons. (4) fewer neutrons. 20. Whatnuclear are two equation? properties that a radioactive 13. Wmusthich contain radioactive atoms emission with is deflected isotope that is used in medical diagnoses (1) stable nuclei. 198 0 26. Wtowardhen an the atom negative emits electrode an alpha in particle a magnetic, its must have? X → 80Hg + −1e massfield?(2) unstable number nuclei. (1) short half-life and be quickly eliminated (1) 198Tl (3) 198Hg (1)(3) positronan even number of nucleons per nucleus. from81 the body. 79 (1) decreases by 2. (3) decreases by 4. Keeping a positive attitude during any test will (2)(4) betaan even particle mass number. (2) long198 half-life and be quickly198 eliminated (2) increases by 2. (4) increases by 4. help(2) you79 focusAu on the test and(4) likely81Hg improve (3) electron yourfrom score. the body. 27. W(4)hichgamma radioactive ray isotope emits an alpha 33.(3) shortWhich half-life equation and representsbe slowly eliminated alpha decay? particle? from2 the body2 . 4 14. The changing of a nucleus by bombardment (1) 1H + 1H → 2He + energy (1) iron-53 (4) long half-life and Nbeuc slowlylear Che meliminatedistry 669 with high energy particles is a(n) 3 3 0 Copyrig(2)ht © byphosphorus-32 Holt, Rinehart and Winston. All rights reserved. from(2) Hthe → bodyHe. + e (1) artificial transmutation. 1 2 −1 (3) technetium-99 226 222 4 (2) natural radioactive decay. 21. An (3)artifact88Ra has → one-sixteenth86Rn + 2He of the ratio of (4)(3)radium-226decomposition reaction. carbon-14 to carbon-12 that is found in a (4) 14N + 4He → 16O + 0n 28. A(4) nucleiexample that of has an alphatoo many emission. protons can modern-day7 object.2 How8 many+ 1half-lives have elapsed? 15.becomeWhich radioactive more stable emission as a result has the of same 34. What does X represent in the following (1) one (1)masselectron and charge capture as an. electron? nuclear equation? (2) two (2)(1)nuclearpositron fusion. (3) three X → 222Rn + 4He (3)(2)betabeta decayparticle. 86 2 (4) four (3) alpha particle 226 222 (4) gamma release. (1) 88Rn (3) 88Ra (4) gamma ray 22. Every radioactive isotope 218 222 29. Examine the following nuclear equation. (1) emits(2) 84 anPo alpha particle. (4) 86Rn 16. The energy released during a fission reac- 14 14 0 (2) has a characteristic half-life. tion is the result6C →of the7N conversion + −1e of 35. What type of nuclear reaction is repre- (3) has the same atomic mass. (1) protons into alpha particles. sented by the following equation? This radioactive decay is an example of (4) has an atomic number greater than 92. (2) neutrons into nucleons. (1) positron emission. 235U 1n 139Ba 94Kr 31n energy (3) energy into mass. 92 + 0 → 56 + 36 + 0 + (2) beta decay. (4) mass into energy. (1) nuclear fusion (3) electron capture. (2) natural radioactive decay (4) alpha decay. (3) decomposition 670 Chapter 18 (4) nuclear fission Copyright © by Holt, Rinehart and Winston. All rights reserved.

Nuclear Chemistry 671

23. The nucleus of the nuclide protactinium-231 30. Identify a product of the radioactive decay contains of cesium-137. (1) 91 protons and 140 neutrons. (1) positron (2) 91 protons and 140 electrons. (2) cesium-136 (3) 91 neutrons and 140 protons. (3) beta particle (4) 91 neutrons and 140 electrons. (4) alpha particle

24. How many nucleons are present in an atom 31. Examine the following nuclear equation. of thorium-232? 131I → 131Xe + A (1) 323 (3) 232 53 54 (2) 90 (4) 142 What particle is represented by A? (1) proton (3) alpha particle 25. Compared to a carbon-12 nucleus, a (2) neutron (4) beta particle carbon-14 nucleus has two (1) fewer protons. (3) more neutrons. 32. What does X represent in the following (2) more protons. (4) fewer neutrons. nuclear equation?

198 0 26. When an atom emits an alpha particle, its X → 80Hg + −1e mass number (1) 198Tl (3) 198Hg (1) decreases by 2. (3) decreases by 4. 81 79 198 198 (2) increases by 2. (4) increases by 4. (2) 79Au (4) 81Hg 27. Which radioactive isotope emits an alpha 33. Which equation represents alpha decay? particle? (1) 2H + 2H → 4He + energy (1) iron-53 1 1 2 3 3 0 (2) phosphorus-32 (2) 1H → 2He + −1e (3) technetium-99 (3) 226Ra → 222Rn + 4He (4) radium-226 88 86 2 (4) 14N + 4He → 16O + 0n 28. A nuclei that has too many protons can 7 2 8 +1 become more stable as a result of 34. What does X represent in the following (1) electron capture. nuclear equation? (2) nuclear fusion. X → 222Rn + 4He (3) beta decay. 86 2 Section Review 226 222 (4) gamma release. (1) 88Rn (3) 88Ra 218 222 29. Examine the following nuclear equation. (2) 84Po (4) 86Rn 14 14 0 6C → 7N + −1e 35. What type of nuclear reaction is represented by the following equation? This radioactive decay is an example of 235 1 139 94 1 (1) positron emission. 92U + 0n → 56Ba + 36Kr + 30n + energy (2) beta decay. (1) nuclear fusion (3) electron capture. (2) natural radioactive decay (4) alpha decay. (3) decomposition (4) nuclear fission 10. A nucleus of helium-4 weighs 0.0304 amu 17. Which describes a positron? less than the sum of the masses of its pro- (1) same mass and charge as an electron Nuclear Chemistry 671 tons and neutrons. This mass defect can best (2) mass of a proton and a +1 charge be explained by Copyright (3)© by Hmassolt, Rine hofart aannd W electroninston. All right sand reserv ead. +1 charge (1) the conversion of mass to nuclear bind- (4) heaviest subatomic particle ing energy. 18. Which isotope is most likely to be used as a (2) a contradiction to the law of conserva- fuel for a fission reaction? tion of mass. (1) oxygen-18 (3) miscalculation of the mass of a proton. (2) hydrogen-3 (4) miscalculation of the mass of a neutron. (3) calcium-41 11. Which Group 16 element has no stable (4) uranium-235 isotope? 19. What is the major obstacle to fusing two (1) O (3) Te nuclei to form a single nucleus? (2) S (4) Po (1) small size of the nuclei 12. Which radioactive emission has a charge of (2) small mass of the nuclei +2 and a mass of 4 amu? (3) repulsion of the nuclei (1) alpha particle (3) positron (4) number of neutrons in the nuclei (2) beta particle (4) gamma ray 20. What are two properties that a radioactive 13. Which radioactive emission is deflected isotope that is used in medical diagnoses toward the negative electrode in a magnetic must have? field? (1) short half-life and be quickly eliminated (1) positron from the body. (2) beta particle (2) long half-life and be quickly eliminated (3) electron from the body. (4) gamma ray (3) short half-life and be slowly eliminated from the body. 14. The changing of a nucleus by bombardment (4) long half-life and be slowly eliminated with high energy particles is a(n) from the body. (1) artificial transmutation. (2) natural radioactive decay. 21. An artifact has one-sixteenth of the ratio of (3) decomposition reaction. carbon-14 to carbon-12 that is found in a (4) example of an alpha emission. modern-day object. How many half-lives have elapsed? 15. Which radioactive emission has the same (1) one mass and charge as an electron? (2) two (1) positron (3) three (2) beta particle (4) four (3) alpha particle (4) gamma ray 22. Every radioactive isotope (1) emits an alpha particle. 16. The energy released during a fission reac- (2) has a characteristic half-life. tion is the result of the conversion of (3) has the same atomic mass. (1) protons into alpha particles. (4) has an atomic number greater than 92. (2) neutrons into nucleons. (3) energy into mass. (4) mass into energy.

670 Chapter 18

14 14 beta particle 6 C → 7 N + 0 −1e

14 14 0 + 6C → 7N + −1e 2␥

Stabilizing Nuclei by Converting Protons into Neutrons positron electron energy in the form of 0 One+ way that0 a nucleus that has too many protons can become more sta- +1e −1e → gamma rays ble is by a process called electron capture. In this process, the nucleus merely absorbs one of the atom’s electrons, usually from the 1s orbital. This process changes a proton into a neutron and decreases the atomic Gamma numberRays A byre oneAls.oT heEm massitte dnumber in Pos staysitron the Em sameissi.on 1 0 electron capture 1 Some nuclei that have too many+1 pprotons+ −1e  can become→ stable0n by emitting positrons, which are the antiparticles of electronsSection.The Rprocessevie isw similar to electron captureA typical in nucleus that aWhat protonthat kind decays ofis nuclearchanged by reactionthis intoprocess is shown a neutron. is below? chromium-51.However, in positron emission, a proton emits51 a positron.0 electron capture 51 24Cr + −1e → 23V + ␥ 1 positron emission 1 0 p (1)alpha-decay→ n + e The final symbol+1 in the equation, ␥0, indicates+1 the release of gamma rays. (2) beta-decay Notice thatMany when nuclear a proton changes changes leave into a anucleus neutron in by an emitting energetic a positron,or excited state. TTopicopic LinkLink (3) positron emission the mass Wnumberhen th stayse nu ctheleu sames(4) staelectronb, butilize thes ,captureit atomic rel eas enumbers energ ydecreases in the f obyrm one of. gamma Refer to the “Atoms and Moles” The isotoperay schromium-49. Figure 8 sho wdecayss a thu bynd ethisrst oprocessrm dur,inasg shownwhich gbyam thema modelrays may also chapter for a discussion of in Figure b9.e produced. Below is an example of: electromagnetic waves. 49Cr 49V 0e 24 → 23 + +1 Nuclear Chemistry 649 (1) alpha-decay Another Cexampleopyright © by H ooflt, R inaneha rtunstable and Winston. A lnucleusl rights reserve dthat. emits a positron is potas- (2) beta-decay sium-38, which changes into argon-38. (3) positron emission (4)38 electron38 capture0 19K → 18Ar + +1e The positron is the opposite of an electron. Unlike a beta particle, a positron seldom makes it into the surroundings. Instead, the positron usually collides with an electron, its antiparticle. Any time a particle collides with its antiparticle, all of the masses of the two particles are converted entirely into electromagnetic energy or gamma rays. This process is called annihilation of matter, which is illustrated in Figure 9.

650 Chapter 18

Copyright © by Holt, Rinehart and Winston. All rights reserved. Nuucclleeaarr EEqquuaattioionnss M Muusts tB Be eB Balaalnacnecded NNuucclleeaarr EEqquuaattiioonnss MMuusstt B Bee B Baalalanncceedd www.scilinks.org Look backback at at all all of of the the nuclear nuclear equations equations that that have have appeared appeared so farso farin this in this www.scilinks.org LookLook back back at at all all of of the the nuclear nuclear equations equations that that have have appeared appeared so so far far in in this this Topic:Topic:NuclearNuclear Reactions Reactionswwwwww.sci.scilinks.orglinks.orgchapter. Notice thatBalancing the sum of theNuclear mass numbers Equations (superscripts) on one Topic: Nuclear Reactionschapter. Notice that the sum of the mass numbers (superscripts) on one SciSciLinksLinks code: code:HW4088HW4088Topic: Nuclear Reactions chapterchapter..NoticeNotice thatthat thethe sum sum of of the the mass mass numbers numbers (superscripts) (superscripts) on on one one SciLinks code: HW4088 side ofof thethe equationequation always always equals equals the the sum sum of ofthe the mass mass numbers numbers on onthe the SciLinks code: HW4088 sideside ofof thethe equationequation alwaysalways equals equals the the sum sum of of the the mass mass numbers numbers on on the the other sideside ofof thethe equation.equation.LikewiseLikewise, the, the sums sums of ofthe the atomic atomic numbers numbers otherotherNotic sidesidee: the ofof thesumthe equation.ofequation. the massLikewise numbersLikewise ,(superscripts,thethe sumssums of) ofon the onethe atomic sideatomic of thenumbers numbers (subscripts) on on each each side side of of the the equation equation are are equal. equal.LookLook at theat the following following (subscripts)(subscripts)equation AL on onW each AeachYS equalsside side of of the the the sum equation equation of the arema aress equal. equal.numbersLookLook on at theat the the other following following nuclear equationsside o,f andthe noticeequati othatn. S itheymilar balancely, the s uinm sterms of th ofe abothtomi cmass num andbers nuclear equationsnuclearnuclear equations equations, and notice,,andand that notice notice they that that balance they they balance balance in terms in in terms termsof both of of both bothmass mass mass and and and nuclear charge(subscripts. ) on each side of the equation are equal. nuclear chargenuclearnuclear. chargecharge.. 238 234238 4234 [2384 = 234[238 + 4 mass= 234 balance]+ 4 mass balance] 238 234 4 [238 = 234[238 + 4 mass234 balance]4 mass balance] 92U → 2389092UTh  →+ 2He23490Th[92 + =24He90 +[922 charge = 90= + balance]2 +charge balance] 92U → 9290UT h→ + 290HeTh [92+ 2 He= 90 [92+ 2 =charge90 + 2 balance]charge balance]

234 234234 2340 [234 = 0234[234 + 0 mass= 234 balance]+ 0 mass balance] 234 234234Th → 2340Pa [234+ =0e 234[234 + 0= mass234 + balance]0 mass balance] 90Th → 9091TPah + −191e [90Pa =+− 911 +e [90(−1) = charge91 + (− 1)balance] charge balance] 90Th → 9091Pa→ + −911e [90 =−191 +[90(− =1)91 charge + (−1) balance]charge balance] Remember that whenever the atomic number changes, the identity of the RememberRemember that that whenever whenever that whenever the the atomic atomic the number atomicnumber changesnumber changes, changesthe, the identity identity, the identityof the of the of the element changeselement. Inchanges the above. In the examples above examples, uranium, uranium changes changes into thorium, into thorium, element changeselementRemember. Inchanges the: wheneabove. In thever examples abovethe atomic examples, uraniumnumber, uranium changes, changes changes the into identity thorium,into ofthorium, and thoriumand changes thorium into changes protactinium. into protactinium. and thoriumandthe changes thorium element intochanges.changes protactinium. into protactinium.

11 SSKKII1111LLLLSSSSSSKKKKIIIILLLLLLLLSSSS 11 SSKKIILLLLSS BBaallaanncciinngg NNuucclleeaarr EEqquuaattiioonnss BalancTinheg following Nucle rulesar E arequ helpfulation fors balancing a nuclear equation and BalancTinheg following Nucle rulesar Eareq uhelpfulatio forns balancing a nuclear equation and The followingfor identifying rules are ahelpful reactant for or balancing a product a in nuclear a nuclear equation reaction. and forThe identifying followingfor identifying arules reactant are a helpfulor reactant a product for or balancinga inproduct a nuclear in a anuclear reaction.nuclear equation reaction. and for identifying1. Check a reactant mass and or atomica product numbers. in a nuclear reaction. 1. Check mass and atomic numbers. 1. Check mass• The and total atomic of the massnumbers. numbers must be the same on both sides • The total of the mass numbers must be the same on both sides 1.•CheckThe total mass ofof the theand equation.mass atomic numbers numbers. must be the same on both sides of the equation. •ofThe the total equation.• T ofhe thetotal mass of the numbers atomic numbers must be must the samebe the onsame both on sidesboth • The total of the atomic numbers must be the same on both • Tofhe the total equation. sidesof the of atomic the equation. numbersIn othermust bewords the, thesame nuclear on both charges sides of the equation. In other words, the nuclear charges •sidesThe totalof themust of equation. the balance atomic.In othernumbers words must, the be nuclear the same charges on both must balance. must balance• If the. atomic number of an element changes, the identity of the sides of• the If the equation. atomic numberIn other of words an element, the nuclear changes ,chargesthe identity of the • If the atomicelement number also ofchanges an element. changes, the identity of the must balanceelement. also changes. • elementIf the atomic also changes number. of an element changes, the identity of the 2. Determine how nuclear reactions change mass and element2. Determine also changes ho.w nuclear reactions change mass and 2. Determineatomic how numbers.nuclear reactions change mass and •atomicIf a bet anumbers. particle, 0e, is released, the mass number does not atomic numbers. −10 2. Determine• I fho a bwet anuclear particle, −reactions1e, is releas echanged, the mass mass number and does not • If a beta pchangearticle, but0e, tihs erealteoamseicd n, tuhmebmasser inc numberreases by doesone. not atomic numbers.change −but1 the0 atomic number increases by one. • If a positron, +1e is released, the mass number does not change change but the atom0ic nu0mber increases by one. • If a positron, 1e is released, the mass number does not change • If a beta bpuatr ttihc0elea,t−o1me,icis+n ruemlebaesredde,ctrheeasmasses by onumberne. does not • If a positron,but +t1heeisat oreleased,m1ic numbtheer d massecrea snumberes by on edoes. not change change• butIf a t neutron,he atomi0c1n n, uism released,ber incrtheeas emasss by numberone. decreases by one but the a•toIfm aic neutron,n0umber d0nec, rise areleased,ses by onthee. mass number decreases by one • If a positron,and 1thee atomicis released, numberthe does mass not number change. does not change • If a neutron,and then+,1is atomic released, numberthe mass does numbernot change decreases. by one but the•aElectrontom0ic nu capturember de doescrea snotes bchangey one. the mass number but and the atomic•decreasesElectron1 number capturethe atomic does does notnumber not change change by. one the. mass number but • If a neutron, 0n, is released, the mass number decreases by one • Electron• captureEmissiondecreases does of the an not atomic alpha change particlenumber the, 4massbyHe one, decreasesnumber. but the mass and the atomic number does not change24 . decreases•number Emissionthe atomic by of four numberan alphaand decreases by particle one. , the2He atomic, decreases number the bymass two . • Electron capture does not change4 the mass number but • Emission• ofWnumber henan alphaa positronby four particle andand, decreases2anHe electron, decreases the collide atomic the, energymass number in theby twoform. of numberdecreases •byW thefourhen atomic anda positron decreases number and the anby electron atomicone. numbercollide, energyby two in. the form of gamma rays is generated.4 •• WEmissionhen a positron gammaof an alpha andrays an isparticle generated.electron, 2He collide, decreases, energy the in the mass form of gammanumber rays by fouris generated. and decreases the atomic number by two. 652 Chapter 18 • When a positron and an electron collide, energy in the form of 652 Chapter 18 gamma rays is generated. Copyright © by Holt, Rinehart and Winston. All rights reserved. 652 Chapter 18 Copyright © by Holt, Rinehart and Winston. All rights reserved.

Copyright © by Holt, Rinehart and Winston. All rights reserved. SAM PLE PROBLE M A SSSSAAAMMMPPPPLLLLEEEE PPPPRRRROOOOBBBBLLLLLEEEEEMMMMM AAAAA Balancing a Nuclear Equation BBaallaanncinngg aa NNuucclleeaarr EEqquuaattioionn Identify the product formed when polonium-212 emits an alpha particle. IIddeenntify tthhee pprroodduucctt ffoorrmmeedd w whheenn p poololonniuiumm-2-1221 2e memitsi tas na nal pahlpah paa prtairctliec.le. 11 GatherGather information.information. 1 Gather information. 212 • Check the periodic table to write the symbol for polonium-212:21284Po. • Check the periodic table to write the symbol for polonium-212: 84212Po. • Check the periodic table to write the symbol4 for polonium-212: 84Po. • Write the symbol for an alpha particle:42He. • Write the symbol for an alpha particle: 2He4 . • Write the symbol for an alpha particle: 2He. 2 Plan your work. 22 PlanPlan your work.work. ••SetSet upup thethe nuclearnuclear equation. • Set up the nuclear equation. 212212 44 2128484PPoo →→22He4He ++?? 84Po → 2He + ?

33 Calculate.Calculate. PRACTICEPRACTICEPRACTICEPRACTICE HINTHINT HINTHINT 3 Calculate. PRACTICEPRACTICE HINTHINT ••TThehe sumssums ofof thethe mass numbersnumbers mustmust bebe thethe same same on on both both sides sides of of the the • The sums of the mass numbers must be the same on both sides of the UnlikeUnlike a chemicala chemical equation:equation:SSAAMMPPLLEE PP212212RROO =B=BLL44EE +MMA; AA AA == 212212 −−44 ==208208 Unlike a chemical equation: 212 = 4 + A; A = 212 − 4 = 208 equation,equation,thethe elements elements Balancing a Nuclear Equation areareequation, usually usually different thedifferent elements on on 212212Po 44He 208208? Identify the product formed when polon2128484iumP-o21 2→ →emi2t2s4 Hean al +p+ha p208art?icle. eacheachare side usuallyside of of a balancedadifferent balanced on 84Po → 2He + ? each side of a balanced 1 Gather information. nuclearnuclear equation. equation. ••TThehe sumssums ofof thethe atomic numbersnumbers mustmust bebe the212the same same on on both both sides sides of of nuclear equation. • Check the periodic table to write the symbol for polonium-212: 84Po. • The sums of the atomic numbers4 must be the same on both sides of • theWritethe equation: equation:the symbol for84 84an alpha= 2 particle:+ Z;Z; ZZ2 He ==.8484 −−22 ==8282 the equation: 84 = 2 + Z; Z = 84 − 2 = 82 2 Plan your work. 212212 44 208208 • Set up the nuclear equation. 84PPoo → 2HeHe + 82?? 21284 → 24 + 20882 212 4 84Po → 2He + 82? 84Po → 2He + ? ••CheckCheck thethe periodicperiodic table toto identifyidentify thethe elementelement that that has has an an atomic atomic 3•Calculate.numberChecknumber the ofof 82,periodic82, andand complete table to theidentifythe nuclearnuclear the equation. equation.element PRACTICEthatPRACTICE has HINTHINT an atomic • The sums of the mass numbers must be the same on both sides of the number of 82, and complete the nuclear equation.Unlike a chemical equation: 212 = 4 + A; A = 212 − 4 212= 208 4 208 equation, the elements 21284Po → 24He + 20882Pb 84Po → 2He + 82Pb are usually different on 212Po → 4He212 + 208? 4 208 84 2 84Po → 2He + 82Pb each side of a balanced nuclear equation. • The sums of the atomic numbers must be the same on both sides of 44 VVerifyerifythe equation: youryour84 =results.results.2 + Z; Z = 84 − 2 = 82 4 V•erifyEmission your of results. an 212alpha particle4 208 does decrease the atomic number by • Emission of an alpha84Po → particle2He + 82? does decrease the atomic number by two (from 84 to 82) and does decrease the mass number by four •• twoCheckEmission (from the periodic of84 an tableto alpha 82)to identify and particle the does element decrease does that has decrease an the atomic mass the number atomic numberby four by (from 212 to 208). (fromnumbertwo (from of 212 82, and to 84 complete 208). to 82) the and nuclear does equation. decrease the mass number by four 212 4 208 (from 212 to 208).84Po → 2He + 82Pb PRACTIC E 4 Verify your results. PRACTIC E •WriteEmissionBalancing balanced of an alpha Nuclear particle equations does Equation decrease for the the Practiceatomic following number bynuclear equationsP. RACTIC E Writetwo (from balanced 84 to 82) and equations does decrease forthe mass the number following by four nuclear equations. 1 Write218(fromP o212 balanced to 208).4He equations? for the following nuclear equations. 21884 → 42 + OBLEMOBLEMGG 1 84Po → 2He + ? PRPR VVIINN 218 4 SSPRPROOLLOBLEMOBLEMLLLLNNGG 1 142 Po → He142 + ? KKLILIVVII 2 84Pm + ? 2→ Nd PRACTIC E SSSSOOOBLEMOBLEMIILLLLGG 14261 14260 PRPRSSKK VVIINN 2 Write61Pm balanced + ? equations→ 60 Ndfor the following nuclear equations. SSOOLL LL 142 142 IILL 218 4 SSKK 21 25384PoPm → 2+He4? + ?→ 1 Nd 61Es He 60n ? OBLEMOBLEMGG 3 25399 + 42 → 10 + PRPR LLVVIINN SSOO IILLLL 3 142 Es + He142 → n + ? SSKK 2 9961Pm + ? →2 60Nd 0 3 253Es + 4He → 1n + ? 4 253Write99 4 the2 balanced1 0 nuclear equation that shows how sodium-22 3 99Es + 2He → 0n + ? 4 Writechanges the into balanced neon-22. nuclear equation that shows how sodium-22 44 changesWriteWrite the thebalanced into balanced neon-22.nuclear equation nuclear that shows equation how sodium-22 that shows how sodium-22 changeschanges into intoneon-22. neon-22.

Nuclear Chemistry 653 Nuclear Chemistry 653 Nuclear Chemistry 653 Copyright © by Holt, Rinehart and Winston. All rights reserved. Copyright © by Holt, Rinehart and Winston. All rights reserved. Nuclear Chemistry 653 Copyright © by Holt, Rinehart and Winston. All rights reserved.

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?%@(%'1)*+@(-&'@0'*&1*&0&2+&4',5'%C ?%@(%'1)*+@(-&'@0'*&1*&0&2+&4',5'%C !# 1.0@+*.2 9# ,&+) :# 2&3+*.2 <# )-1%) !# 1.0@+*.2 9# ,&+) :# 2&3+*.2 <# )-1%) Section 3 – Uses of Nuclear Chemistry

Table T Important Formulas and Equations

d = density m Density d = m = mass V V = volume

given mass (g) Mole Calculations number of moles = gram-formula mass

measured value – accepted value Percent Error % error = ! 100 accepted value

mass of part Percent Composition % composition by mass = ! 100 mass of whole

grams of solute parts per million = ! 1000000 grams of solution

Concentration moles of solute molarity = liters of solution

P = pressure Section 3 – UsesP1V1 Pof2V2 Nuclear Chemistry Combined Gas Law = V = volume T T 1 2 T = temperature (K)

+ – MA = molarity of H MB = molarity of OH Titration MAVA = MBVB VA = volume of acid VB = volume of base

q = mC!T q = heat Hf = heat of fusion Heat q = mHf m = mass Hv = heat of vaporization q = mHv C = specific heat capacity !T = change in temperature

K = °C + 273 K = kelvin Temperature °C = degrees Celsius

t 1 fraction remaining = T t = total time elapsed ( 2 ) Radioactive Decay T= half-life number of half-life periods = t T

DET 609 (8-03–350,000) 93-93703 93-041 CDC

12 Reference Tables for Physical Setting/CHEMISTRY Chapter 13 Review S E C T I O N S E C T I O N 2 Nuclear Change

KEY TERMS OBJECTIVES KEY TERMS OBJECTIVES • radioactivity • radioactivity 1 Predict the particles and electromagnetic waves produced by • radioactivity 1 Predict the particles and electromagnetic waves produced by • beta particle 1 different types of radioactive decay, and write equations for • beta particle different types of radioactive decay, and write equations for • beta particle nucleardifferent decays. types of radioactive decay, and write equations for • gamma ray nuclear decays. • gamma ray • nuclear fission 2 Identify examples of nuclear fission, and describe potential benefits • nuclear fission 2 Identify examples of nuclear fission, and describe potential benefits • nuclear fission 2 andIdentify hazardsexamples of its use.of nuclear fission, and describe potential benefits • chain reaction and hazards of its use. • chain reaction Describe nuclear fusion and its potential as an energy source. • critical mass 3 Describe nuclear fusion and its potential as an energy source. • critical mass 3 Describe nuclear fusion and its potential as an energy source. • nuclear fusion • nuclear fusion Figure 9 Nuclei can release positrons Radioactive Decay to form new nuclei. Matter is Radioactive Decay + then converted into energy Radioactive Decay when positrons and electrons Nuclear changes can be easier to understand than chemical changes Nuclear changes can be easier to understand than chemical changes collide and are converted bNeuccaluesaer ocnhlayn ag efse wc atynp ebse oef ansuiecrle ator cuhnadnegresst aoncdcu trh. Oann ec htyepmei cisa lt hceh aspnognes- into gamma rays. because only a few types of nuclear changes occur. One type is the spon- because only a few types of nuclear chapositronnges occur. One type is the spon- 49 taneous change of an 49unstable nucleus t0o form a more stable one. This Cr taneous→ change of an uVnstable +nucleus toe form a more stable one. This 24 taneous change of an 23unstable nucleus t+1o form a more stable one. This change involves the release of particles, electromagnetic waves, or both change involves the release of particles, electromagnetic waves, or both radioactivity and is generally called radioactivity or radioactive decay. Specifically, radioactivity and is generally called radioactivity or radioactive decay. Specifically, the process by which an unstable radioactivity is the spontaneous breakdown of unstaWhenble nu positronsclei to pro aredu ce the process by which an unstable r+adioactivity is the spontaneous breakdo2w␥ n of unstable nuclei to produce nucleusthe process emits by one which or morean unstable parti- particles or energy. Table 1 summarizes the propertiereleas of bsed,oth they the pcaolrtlideicle swith nucleus emits one or more parti- particles or energy. Table 1 summarizes the properties of both the particles clesnucleus or energ emitsy onein the or formmore of parti- particles or energy. Table 1 summarizes the properties of both the particles cles or energy in the form of and the energy released by radioactive decay. nearby electrons. Matter is electromagneticcles or energy in r theadiation form of and the energy released by radioactive decay. electromagnetic radiation positron and telhecter oennergy released by radioactiveenergy dec inay. then converted to energy electromagnetic radiation the form of 0e + 0e → +1 −1 gamma rays (gamma rays). Table 1 Characteristics of Nuclear Particles and Rays Table 1 ChAnniaracterhiistilationcs of Nuc oflea rM Paattrticleres and Rays Particle Mass (amu) Charge Symbol Stopped by Gamma RaysP articleAre Also Emitted Massin Po (amu)sitron EmissioChargen Symbol Stopped by + 1 1 Some nuclei thatProton have too many protons1.007 can 276 become 47 stable1 by emittingp, p+, 1p, 1H a few sheets Proton 1.007 276 47 +1 p, p+, +1p, 1H a few sheets Proton 1.007 276 47 +1 p, p+, +1p, 1H a few sheets positrons, whichProton are the antiparticles1.007 of electrons 276 47.The process+1 is similarp, top , +1 p, 1H ofa few paper sheets electron capture in that a proton is changed into a neutron. However, in of paper 0 1 positron emission,Neutrona proton emits a positron.1.008 664 90 0 n, n0, 01n a few centi- Neutron 1.008 664 90 0 n, n0, 01n a few centi- Neutron 1.008 664 90 0 n, n , 0 n a few centi- 1 positron emission 1 0 meters of lead www.scilinks.org p → n + e meters of lead www.scilinks.org +1 0 +1 meters of lead Twwwopic: Radioactive.scilinks.org Decay − 0 Topic: Radioactive Decay ␤ particle 0.000 548 580 −1 ␤, ␤−, −01e* a few sheets of SciTopic:Links Radioactive code: HW4106 Decay Notice that when␤ particle a proton changes into0.000 a neutron 548 580 by emitting−1 a positron,␤, ␤−, −01e* a few sheets of SciLinks code: HW4106 ␤ particle 0.000 548 580 −1 ␤, ␤ , −1e* a few sheets of SciTopicLinks Link code: HW4106 (electron) 1 aluminum foil the mass number(electron) stays the same, but the atomic number decreases by one. aluminum foil Refer to the “Atoms and Moles” The isotope chromium-49 decays by this process, as shown by the model+ 0 Positron† 0.000 548 580 +1 ␤+, 0e* same as electron chapter for a discussion of Positron† 0.000 548 580 +1 ␤+, +01e* same as electron in Figure 9. Positron† 0.000 548 580 +1 ␤ , +1e* same as electron electromagnetic waves. 49 49 0 + +1 2+ 4 ␣ particle 24Cr → 4.00123V + +4741e 92 +2 ␣, ␣2+, 4He skin or one ␣ particle 4.001 474 92 +2 ␣, ␣2+, 42He skin or one ␣ particle 4.001 474 92 +2 ␣, ␣ , 2He skin or one (He-4particle nucleus) 4.001 474 92 +2 , , 2He sheetskin or of one paper Another example(He-4 of annucleus) unstable nucleus that emits a positron is potas- sheet of paper sium-38, whichGamma changes intoray argon-38.0 0 ␥ several centi- Gamma ray 0 0 ␥ several centi- Gamma ray38 380 0e 0 ␥ metersseveral ofcenti- lead 19K → 18Ar + +1 meters of lead www.scilinks.org meters of lead www.scilinks.orgThe positron is the opposite of an electron. Unlike a beta particle, a Twwwopic: Radioactive.scilinks.org Emissions Topic: Radioactive Emissions SciTopic:Links Radioactive code: HW4107 Emissionspositron seldom*T makeshe superscript it into the surroundingszero in the .symbolsInstead, the for positron electron usu- and positron does not mean SciLinks code: HW4107 *The superscript zero in the symbols for electron and positron does not mean SciLinks code: HW4107 ally collides withthat*T hean they electron,superscript haveits zero antiparticle zero mass in .theIt. Any means symbols time theira particlefor masselectron collides number and positronis zero. does not mean with its antiparticlethat they, all of have the masseszero mass of the. It two means particles their are mass converted number is zero. entirely into electromagnetic†The positron energy is the or antiparticle gamma rays. ofThis the process electron. is calledEach particle has an antiparticle, †The positron is the antiparticle of the electron. Each particle has an antiparticle, annihilation ofbut†T matterhe only positron, which the positronis isillustrated the antiparticle is frequentlyin Figure 9. of involvedthe electron. in nuclearEach particlechanges has. an antiparticle, but only the positron is frequently involved in nuclear changes. 0 0 annihilation ␥ 648 Chapter 18 −1e + +1e → 2 648 Chapter 18 648 Chapter 18 The gamma rays from electron-positron annihilation have a characteristic Copyright © by Holt, Rinehart and Winston. All rights reserved. wavelength; therefore, these rays can be used to identify nuclei thatCop ydecayright © by Holt, Rinehart and Winston. All rights reserved. Copyright © by Holt, Rinehart and Winston. All rights reserved. by positron emission. Such gamma rays have been detected coming from the center of the Milky Way galaxy.

650 Chapter 18