Chapter 2 Nuclear Chemistry - Copy

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<ul><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 1/26</p><p>GENERAL CHEMISTRY</p><p>CHAPTER 2: NUCLEAR CHEMISTRY</p><p> Nuclear chemistry is the study of reactions involving changes in atomic nuclei.</p><p> This branch of chemistry began with the discovery of natural radioactivity by</p><p>Antoine Becquerel and grew as a result of subsequent investigations by Pierre</p><p>and Marie Curie and many others.</p><p> Nuclear chemistry is very much in the news today. In addition to applications in</p><p>the manufacture of atomic bombs, hydrogen bombs, and neutron bombs, even</p><p>the peaceful use of nuclear energy has become controversial, in part because of</p><p>safety concerns about nuclear power plants and also because of problems with</p><p>radioactive waste disposal.</p><p> In this chapter, we will study nuclear reactions, the stability of the atomic nucleus,</p><p>radioactivity, and the effects of radiation on biological systems.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 2/26</p><p>GENERAL CHEMISTRY</p><p>CHAPTER 2: NUCLEAR CHEMISTRY</p><p>2.1RadioactivityNuclear reaction Chemical reaction</p><p>Elements may be converted fromone to another</p><p>No new elements can be produced</p><p>Particles within the nucleus are</p><p>involved</p><p>Only the electrons participate</p><p>Nuclide Is an atom characterized by a definite atomic</p><p>number and mass number</p><p>Atomic number (Z) The number of protons in a nuclide</p><p>Mass number (A) The total number protons and neutrons</p><p>1. Isotopes: Atoms of the same element can have different numbers of neutrons</p><p> For example, the most common isotope of hydrogen has no neutrons at all.</p><p> There is also a hydrogen isotope called deuterium with one neutron and</p><p>another tritium with two neutrons.</p><p>Lithium-6 Lithium-7 Lithium-8</p><p>No. of electron 3 3 3</p><p>No. of proton 3 3 3</p><p>No. of neutron 3 4 5</p><p>2. Two types of nuclear reactions:</p><p>Radioactive Decay</p><p> In this process the nucleus spontaneously disintegrates (decay), giving off</p><p>radiation.</p><p>Nuclear bombardment reactions</p><p> A nucleus is bombardedby another nucleus or a nuclear particle.</p><p>3. Nuclear decay reactions : For example, if we had a sample of an element whose half</p><p>life had been determined to be ten days, all we could be sure of is that in ten days</p><p>only half the original specimen would remain -- the other half having beentransformed into some other collection of nuclides and/or decay particles.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 3/26</p><p>GENERAL CHEMISTRY</p><p>4. In a nuclear bombardment reaction, a nucleus is struck by another nucleus or by a</p><p>nuclear particle of sufficient energy to cause the original nucleus to be converted</p><p>into a product nucleus.</p><p>5. Nuclear equations:</p><p> Decay of uranium -238</p><p> You can represent the uranium-238 nucleus by the nuclide symbol</p><p> The products are thorium-234 and helium-4</p><p> The superscript equals the mass number</p><p> The subscript equals the atomic number</p><p> Potassium-40 is a naturally occurring radioactive isotope. It decays to</p><p>calsium-40 by beta emission.</p><p>6. Nuclear Stability:</p><p> How to use simple rules to predict the stability of nuclei?</p><p> Ask the following questions:</p><p>i. Is the atomic number Z &gt; 83?</p><p>ii. Is atomic number or mass number a magic number?</p><p>iii. Are the nucleons paired?</p><p>iv. Does the nucleus lie in the band of stability?</p><p>(i) Is atomic number &gt; 83?</p><p>o The band of stability terminate at Z = 82. Nuclides of Z &gt; 83 are not</p><p>stable. Nuclides of Z &gt; 83 often decay by alpha emission.</p><p>o It appears that when the number of protons becomes very large, the</p><p>proton-proton repulsions become so great that stable nuclides are</p><p>impossible.</p><p>o No stable nuclides are known with atomic numbers greater than 83 .</p><p>(ii)Magic Number</p><p>o The shell model of the nucleussays that protons and neutrons exist in</p><p>shells.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 4/26</p><p>GENERAL CHEMISTRY</p><p>o This explains why nuclei with certain number of protons and neutrons</p><p>appear to be stable.</p><p>o These numbers are called magic numbers.</p><p>o A magic number is the number of nuclear particles in a completed shell of</p><p>protons or neutrons.</p><p>o Helium contains 2 protons and 2 neutrons.</p><p>o That is contains a magic number of protons (2) and a magic number of</p><p>neutrons (2)</p><p>o Calcium contains 82 protons ( magic number) , 126 neutrons (magic</p><p>number)</p><p>Proton Neutron</p><p>2</p><p>8</p><p>20</p><p>28</p><p>50</p><p>82</p><p>114</p><p>2</p><p>8</p><p>20</p><p>28</p><p>50</p><p>82</p><p>126</p><p>(iii)Are the Nucleons Paired?</p><p>o Nuclides with even numbers of nucleons enjoy special stability.</p><p>o In the odd-even rule, when the numbers of neutrons and protons in the</p><p>nucleus are both even numbers, the isotope tends to be far more stablethan when they are both odd.</p><p>o Out of all the 264 stable isotopes, only 5 have both odd numbers of both,</p><p>whereas 157 have even numbers of both and the rest have a mixed</p><p>number.</p><p>(iv)Band of Stability</p><p>o A plot of the number of protons (Z) versus the number of neutrons (N)</p><p>reveals the band of stability, the region in which stable nuclides lie in.</p><p>o For nuclides up to Z=20, the ratio of neutrons to protons is about 1.0 to</p><p>1.1.</p><p>o AsZincreases, the neutron-to-proton ratio increases to about 1.5.</p><p>o This is due to increasing repulsions of protons from their electric charges.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 5/26</p><p>GENERAL CHEMISTRY</p><p>o More neutrons are required to give attractive nuclear forces to balance</p><p>these repulsions.</p><p>7. Types of nuclear radioactive decay:</p><p>i. Alpha emissions</p><p>o Emission of a nucleus or alpha particle</p><p>o All nuclides with Z &gt; 83 are radioactive</p><p>o Example: radioactive decay of radium-226</p><p>o The product nucleus has an atomic number that is two less and</p><p>mass number that is four less than original nucleus</p><p>ii. Beta emission</p><p>o Emission of a high-speed electron from an unstable nucleuso Neutron-to-proton ratio too large</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 6/26</p><p>GENERAL CHEMISTRY</p><p>o beta emission is equivalent to the conversion of a neutron to a proton</p><p>iii. Positron emission</p><p>o Positron is a particle identical to an electron in mass but having a</p><p>positive charge instead of a negative chargeo Positron emission is equivalent to the conversion of a proton to a</p><p>neutron.</p><p>o Neutron-to-proton ratio too small</p><p>o It occurs most often the lighter elements</p><p>iv. Electron capture</p><p>o Is about the decay of an unstable nucleus by capturing an electron</p><p>from an inner orbital of an atom.</p><p>o Neutron-to-proton ratio too small</p><p>o It occurs most often with heavier elements</p><p>v. Gamma emission</p><p>o Emission from an excited nucleus, corresponding to radiation with</p><p>a short wavelength of about 10-12m</p><p>o The excited state is an unstable and goes to a lower energy state</p><p>with the emission of electromagnetic radiation</p><p>o A metastable nucleus is a nucleus in an excited state with a lifetime</p><p>ofat least one nanosecond</p><p>o The product nucleus is simply a lower-energy state of the original</p><p>nucleus, so there is no change of atomic number or mass number</p><p>vi. Spontaneous fission</p><p>o Is the spontaneousdecay of an unstable nucleus in which a heavy</p><p>nucleus of mass number greater than 89 splits into lighter nuclei</p><p>and energy is released.</p><p>o Uranium-236 can spontaneously undergo the following nuclear</p><p>reaction</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 7/26</p><p>GENERAL CHEMISTRY</p><p>8. Radioactive Decay Series:</p><p>o Nuclides withZ &gt; 83are</p><p>radioactive.</p><p>o Many of these nuclides</p><p>decay by alpha</p><p>emission by which a</p><p>nucleus reduces its</p><p>atomic number so that</p><p>it becomes more stable.</p><p>o If the nucleus has a verylarge atomic number,</p><p>such as uranium-238,</p><p>the product nucleus is</p><p>also radioactive.</p><p>o This gives rise to a</p><p>radioactive decay</p><p>series.</p><p>o Radioactive decay series, a sequence in which one radioactive nucleus decays to</p><p>a second, which then decays to a third, and so forth. Eventually, a stable nucleus,</p><p>which is an isotope of lead, is reached.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 8/26</p><p>GENERAL CHEMISTRY</p><p>Questions and Answers: 2.1 Radioactivity</p><p>a) 20.33 Rubidium-87, which forms about 28% of natural rubidium, is radioactive,</p><p>decaying by the emission of a single beta particle to strontium-87. Write the nuclear</p><p>equation for this decay of rubidium-87.</p><p>b) 20.34 Write the nuclear equation for the decay of phosphorus- 32 to sulfur-32 by</p><p>beta emission. A phosphorus-32 nucleus emits a beta particle and gives a sulfur-32</p><p>nucleus.</p><p>c) 20.35 Thorium is a naturally occurring radioactive element. Thorium-232 decays by</p><p>emitting a single alpha particle to produce radium-228. Write the nuclear equation</p><p>for this decay of thorium-232.</p><p>d) 20.36 Radon is a radioactive noble gas formed in soil containing radium. Radium-</p><p>226 decays by emitting a single alpha particle to produce radon-222. Write the</p><p>nuclear equation for this decay of radium-226.</p><p>e) 20.37 Fluorine-18 is an artificially produced radioactive isotope. It decays by</p><p>emitting a single positron. Write the nuclear equation for this decay.</p><p>f) 20.38 Scandium-41 is an artificially produced radioactive isotope. It decays by</p><p>emitting a single positron. Write the nuclear equation for this decay.</p><p>g) 20.39 Polonium was discovered in uranium ores by Marie and Pierre Curie.</p><p>Polonium-210 decays by emitting a single alpha particle. Write the nuclear equation</p><p>for this decay.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 9/26</p><p>GENERAL CHEMISTRY</p><p>h) 20.40 Actinium was discovered in uranium ore residues by Andr-Louis Debierne.</p><p>Actinium-227 decays by emitting a single alpha particle. Write the nuclear equation</p><p>for this decay.</p><p>i) 20.41 From each of the following pairs choose the nuclide that is radioactive. (One is</p><p>known to be radioactive, the other stable.) Explain your choice.</p><p>j) 20.43 Predict the type of radioactive decay process that is likely for each of the</p><p>following nuclides.</p><p>k) 20.44 Predict the type of radioactive decay process that is likely for each of thefollowing nuclides.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 10/26</p><p>GENERAL CHEMISTRY</p><p>2.2Nuclear Bombardment Reactions1. In 1919, Rutherford discovered that it is possible to change the nucleus of one</p><p>element into the nucleus of another element by processes that can be controlled in</p><p>the laboratory.</p><p>2. Transmutationis the change of one element to another by bombarding the nucleus of</p><p>the element with nuclear particles or nuclei.</p><p>3. Rutherford used a radioactive element as a source of alpha particles and allowed</p><p>these particles to collide with nitrogen nuclei.</p><p>4. Nuclear bombardment reaction is often referred to by an</p><p>abbreviated notation.</p><p>5. Transuranium elements:</p><p>o Transuranium elements are the chemical elements with atomic numbers</p><p>greater than 92.</p><p>o None of these elements are stable.</p><p>o They decay radioactively into other elements.</p><p>o [a] Produce neptunium</p><p>o Neptunium (Np) is produced by bombarding uranium-238 with neutron</p><p>o</p><p> This nucleus decayed in a few days by beta emission</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 11/26</p><p>GENERAL CHEMISTRY</p><p>o [b] Produce plutonium</p><p>Questions and Answers: 2.2 Nuclear Bombardment Reactions</p><p>a) 20.47 Write the abbreviated notations for the following bombardment reactions.</p><p>b) 20.49 Write the nuclear equations for the following bombardment reactions. </p><p>c) 20.51 A proton is accelerated to 12.6 MeV per particle. What is this energy in kJ/mol?</p><p>d) 20.53 Fill in the missing parts of the following reactions.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 12/26</p><p>GENERAL CHEMISTRY</p><p>2.3Radiations and Matter: Detection and Biological Effects1. Radiation counters:</p><p>o Two types of devicesionization counters and scintillation countersare</p><p>used to count particles emitted from radioactive nuclei and other nuclear</p><p>processes.</p><p>o Ionization counters detect the production of ions in matter. Scintillation</p><p>counters detect the production of scintillations, or flashes of light.</p><p>2. A Geiger counter, a kind of ionization counter used to count particles emitted by</p><p>radioactive nuclei, consists of a metal tube filled with gas, such as argon.</p><p>o It is used to count particles emitted from radioactive nuclei</p><p>o Alpha and beta particles can be directly detected</p><p>o To detect neutrons, boron trifluoride is added. The alpha particles are</p><p>produced, then can be detected</p><p>3. A scintillation counter is a device that detects nuclear radiation from flashes of light</p><p>generated in a material by the radiation. Aphosphor is a substance that emits flashes</p><p>of light when struck by radiation</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 13/26</p><p>GENERAL CHEMISTRY</p><p>4. Biological Effects and Radiation Dosage</p><p>o Although the quantity of energy dissipated in a biological organism from a</p><p>radiation dosage might be small, the effects can be quite damaging because</p><p>important chemical bonds may be broken.</p><p>o DNA in the chromosomes of the cell is especially affected, which interferes</p><p>with cell divisionn. Cells that divide the fastest, such as those in the blood-</p><p>forming tissue in bone marrow, are most affected by nuclear radiations.</p><p>2.4Rate of Radioactive Decay1. Rate of radioactive decay and half-life:</p><p>o The rate of radioactive decay is proportional to the</p><p>number of radioactive nuclei in the sample.</p><p>o Nt is the number of radioactive nuclei at time t</p><p>o kis the radioactive decay constant</p><p>o Half-life is defined as the time is takes for one-half of the</p><p>nuclei in a sample to decay</p><p>o The shape of exponential decay curve can be seen in the decay of a 1-g</p><p>sample of iodine-131:</p><p>o Note the inverse relationship between the decay constant and the halflife;</p><p>those compounds with very small decay constants have very long half-lives.</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 14/26</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 15/26</p><p>GENERAL CHEMISTRY</p><p>o Example:Phosphorus-32 is a radioactive isotope with a half-life of 14.3 d. A</p><p>biochemist has a vial containing a compound of phosphorus-32. If the</p><p>compound is used in an experiment 5.5 d after the compound was prepared</p><p>what fraction f the radioactive isotope originally present remains? Suppose</p><p>the sample in the vial originally contained 0.28g of phosphorus-32. How</p><p>many grams remain after 5.5d?</p></li><li><p>8/13/2019 Chapter 2 Nuclear Chemistry - Copy</p><p> 16/26</p><p>GENERAL CHEMISTRY</p><p>o Carbon-14 dating</p><p>o The age of organic object can be estimated by radiocarbon dating (14C).</p><p>o The decay reaction as below</p><p>o The half-life is 5730 yearso The 14C in the environment gives a specific activity of 15.3 disintegrations</p><p>per minute per gram of total carbon, that is 0.255 Bq/g</p><p>o Example: A piece of charcoal from a tree killed by the volcanic eruption gave</p><p>7 disintegrations of carbon-14 nuclei per minute per gram of total carbon.</p><p>Present-day carbon (in living matter) gives 15.3 disintegrations per minute</p><p>per gram of total carbon. Determine the date of the volcanic eruption. Recall</p><p>that the half-life of carbon-14 is 5730 years. Answer: 6500 years ago.</p><p>Questions and Answers: 2.4 Rate of Radioactive Decay</p><p>a) 20.57 Tritium, or hydrogen-3, is prepared by bombarding lithium-6 with neutrons.</p><p>A 0.250-mg sample of tritium decays at the rate of 8.94 1010disintegrations per</p><p>second. What is the decay constant (in /s) of tritium, whose atomic mass is 3.02 amu?</p><p>b) 20.59 Sulfur-35 is a radioactive isotope used in chemical and medical research. A0.48-mg sample of sulfur-35 has an activity of 20.4 Ci. What is the decay constant of</p><p>sulfur-35 (in /s)?</p><p>c) 20.60 Sodium-24 is used in medicine to study the circulatory system. A sample</p><p>weighi...</p></li></ul>