6.1_ Nuclear Chemistry_ General Chemistry II w_Lab- 2021- Schiren

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6.1: Nuclear Chemistry 39:37 Nuclear chemistry involves reactions in which nuclei of one or more atoms are altered. This type of chemistry involves much greater energy changes than the normal electron chemistry, which we have discussed in earlier section of this course. Our sun generates its enormous energy by a nuclear reaction, and the destructive hydrogen bomb and atomic bomb explosions are other examples of nuclear reactions. Nuclear reactions are of two basic types: radioactive decay , in which a nucleus spontaneously disintegrates, giving off electrons, neutrons, positrons, protons, helium nuclei, or electromagnetic radiation, such as X-rays or gamma rays. The other type is known as a nuclear bombardment reaction or transmutation , in

which a nucleus is bombarded by another nucleus or a nuclear particle, causing the reactant nucleus to rearrange to give a new product nucleus or nuclei. In nuclear reaction equations, a nucleus (also called a nuclide ) is represented by a nuclear symbol , in which the elemental symbol is accompanied by the atomic number written as a subscript number and the mass number (atomic weight) written as a superscript (whole) number since this symbol represents just one of the isotopes of the element. The nuclear symbols of the mass 37 isotope of chlorine (Cl), the mass 81 isotope of bromine (Br), the mass 14 isotope of carbon (C), and the mass 238 isotope of uranium (U) are shown below: Cl Br C U A nuclear reaction equation can be written for fission and fusion nuclear reactions and describes and represents the changes that are happening in the nucleus of the involved atoms. A nuclear equation must be balanced to insure that mass and charge are conserved in the reaction. In a balanced nuclear equation, the sum of the atomic masses (superscript numbers) of the reactant nuclei on the left side must be equal to the sum of the atomic masses of the product nuclei on the right side and the sum of the atomic numbers (subscript numbers) of the reactant nuclei on the left side must be equal to the sum of the atomic numbers of the product nuclei on the right side, as shown below for the nuclear reaction of N with He : N + He → O + H We will also encounter some other nuclear particles in these nuclear reactions. These are listed below with their description and nuclear symbol. Proton Nucleus of H atom H Alpha (α) particle Helium nucleus He 37 17 81 35 14 6 238 92 14 7 4 2 14 7 4 2 17 8 1 1 1 1 1 4 2

Beta (β) particle Electron e Neutron Neutron n Positron Antiparticle of electron e Gamma photon Radiant energy particle γ Radioactivity is a naturally occurring fission nuclear reaction, in which one naturally unstable nucleus decays spontaneously (that is, without any external influence like added heat or other reactants). There are five types of radioactive decay reactions: (1) alpha (α) particle emission, (2) beta (β) particle emission, (3) gamma (γ) photon emission, (4) positron emission, and (5) electron capture. The products of radioactivity nuclear fission “decay” reactions are new nuclei, energy, and other simpler materials. In alpha particle emission , a radioactive nucleus undergoes a fission reaction producing a new more stable nucleus with lower atomic number and mass number and emits an alpha particle, which is a He nucleus. Many of the heavier radioactive nuclei (atomic number greater than 83) reduce their number of nucleons (protons and neutrons) by undergoing alpha decay. Some examples of radioactive alpha decay are shown below: U → Th + He Rn → Po + He Hg → Pt + He At → Bi + He 0 -1 1 0 0 +1 0 0 4 2 238 92 234 90 4 2 222 86 218 84 4 2 180 80 176 78 4 2 211 85 207 83 4 2

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In beta particle emission , a radioactive nucleus undergoes a fission reaction producing a new more stable nucleus with higher atomic number and the same mass number and emits a beta particle, which is an electron. This occurs as a neutron in the nucleus is converted into a proton and an electron, which is expelled from the nucleus as the beta particle. This conversion of a neutron to a proton keeps the mass number the same. Some examples of radioactive beta decay are shown below: I → Xe + e C → N + e H → He + e In gamma photon emission , a radioactive nucleus undergoes a fission reaction producing a more stable nucleus of the same element with the same atomic number and the same mass number and emits high energy electromagnetic radiation (not a particle with mass), which is a gamma photon. Some examples of radioactive gamma decay are shown below: Tc → Tc + γ (m indicates meta stable) Co → Co + γ Cs → Cs + γ 131 53 131 54 0 -1 14 6 14 7 0 -1 3 1 3 2 0 -1 99m 43 99 43 0 0 60m 27 60 27 0 0 137m 55 137 55 0 0

In positron emission , a radioactive nucleus undergoes a fission reaction producing a new more stable nucleus with lower atomic number and the same mass number and emits a beta particle, which is an electron. This occurs as a proton in the nucleus is converted into a neutron and a positron, which is expelled from the nucleus. This conversion of a proton to a neutron keeps the mass number the same. The expelled positron immediately collides with an electron with both particles disappearing in a process called annihilation with the emission of gamma radiation. Some examples of positron emission are shown below: Al → Mg + e B → Be + e Tc → Mo + e In electron capture , a radioactive nucleus undergoes a fission reaction producing a new more stable nucleus with lower atomic number and the same mass number and emits an X-ray photon. This occurs as the nucleus absorbs one of the atom's inner shell electrons and the captured electron combines with a proton to form a neutron. This conversion of a proton to a neutron keeps the mass number the same. An electron from a higher shell then fills the inner shell vacancy, and energy is given off in the form of an X-ray. Some examples of electron capture are shown below: I + e → Te K + e → Ar Be + e → Li 26 13 26 12 0 +1 8 5 8 4 0 +1 95 43 95 42 0 +1 125 53 0 -1 125 52 40 19 0 -1 40 18 7 4 0 -1 7 3

Nuclear bombardment reaction or transmutation is a process in which a nucleus is bombarded by another nucleus or a nuclear particle, causing the reactant nucleus to rearrange to give a new more stable product nucleus or nuclei. This nuclear process was discovered in 1919 by Ernest Rutherford when he allowed alpha particles ( He ) to collide with the stable N nucleus, causing the following transmutation reaction to occur in which a proton ( H ) was released: N + He → O + H Ernest Rutherford Transmutation reactions like this strengthened the theory that all nuclei contain protons since many of the reactions yielded protons as products. The transmutation reaction below actually lead to the discovery of the neutron: Be + He → C + n 4 2 14 7 1 1 14 7 4 2 17 8 1 1 9 4 4 2 12 6 1 0

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In 1933, Irene and Frederic Joliot-Curie produced the first artificial radioactive nucleus ( P ) by the following transmutation reaction. The unstable P isotope decayed by positron emission by the second reaction shown. Al + He → P + n P → Si + e Irene and Frederic Joliot-Curie Transmutation reactions on heavier (higher atomic number) elements are only successful if the nuclear particle being used to bombard the reactant nucleus is accelerated to very high speeds so as to allow it to penetrate the target nucleus (otherwise it would be deflected by the high positive charge of the great number of protons in that nucleus). These particles are accelerated to high speeds by devices called particle accelerators or cyclotrons . 30 15 30 15 27 13 4 2 30 15 1 0 30 15 30 14 0 +1

A cyclotron Transmutation reactions on heavy nuclei using accelerated particles have made possible the synthesis of the transuranium elements , synthetic elements with atomic numbers greater than that of U, the naturally-occurring element of highest atomic number. The first such elements, Np (Neptunium) and Pu (Plutonium) were produced in 1940 at UC Berkeley by E.M. McMillan and P.H. Abelson by the following set of reactions: U + n → U U → Np + e Np → Pu + e 238 92 1 0 239 92 239 92 239 93 0 -1 239 93 239 94 0 -1

An entire series of synthetic transuranium elements has been produced, including 20 elements from atomic numbers 93 through 112 by way of transmutation reactions. These elements are far from laboratory curiosities, however, with many having commercial utility. Plutonium ( Pu ) is used as a power source for space satellites and pacemakers and Americium ( Am ) is used as part of the alarm circuit in smoke detectors. Practice Problems Complete the following problems. When finished, check your answers with the answer key below. 1) Give three examples of nuclear reactions. 2) List and explain the two basic types of nuclear reactions. 3) Write nuclear symbols for chlorine-35, bromine-79, nitrogen-15 uranium-235. 4) What is a nuclide? 5) Write nuclear symbols for the proton, the α-particle, the β-particle, the neutron, the positron. 6) What is a nucleon? 7) Define radioactivity. 238 94 241 95

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8) Radioactivity nuclear reactions generally have _________ reactant(s) and _________ product(s). 9) List the 5 types of radioactive decay processes and describe each. 10) Balance the following radioactive decay reactions and label each as one of the 5 types. Co → Co + ? Be + ? → Li Hg → Pt + ? H → He + ? Al → Mg + ? 11) Define and explain transmutation. 12) Balance the following transmutation reactions. N + He → ? + H P → ? + e 13) What is a cyclotron and what is it used for? 14) What are the transuranium elements? 60m 27 60 27 7 4 7 3 180 80 176 78 3 1 3 2 26 13 26 12 14 7 4 2 1 1 30 15 0 +1

Answer Key 1) Three examples of nuclear reactions are energy generation by the sun and the destructive hydrogen bomb and atomic bomb explosions. 2)The two basic types of nuclear reactions are radioactive decay in which a nucleus spontaneously disintegrates giving off electrons or neutrons or positrons or protons or helium nuclei or electromagnetic radiation such as X-rays or gamma rays. The other type is known as a nuclear bombardment reaction or transmutation in which a nucleus is bombarded by another nucleus or a nuclear particle causing the reactant nucleus to rearrange to give a new product nucleus or nuclei. 3)The nuclear symbol for chlorine-35 is Cl , for bromine-79 is Br , for nitrogen-15 is N and for uranium-235 is U . 4) A nuclide is a nucleus. 5) The nuclear symbol for the proton is H , for the α-particle is He , for the β- particle is e , for the neutron is n and for the positron is e . 6) A nucleon is any particle found in the nucleus; a proton or a neutron. 7) Radioactivity is a naturally-occurring fission nuclear reaction in which one naturally unstable nucleus decays spontaneously. 8) Radioactivity nuclear reactions generally have one (1) reactant(s) and more than one product(s). 9) The 5 types of radioactive decay processes are: Alpha particle emission in which a radioactive nucleus undergoes a fission reaction producing a new more stable nucleus with lower atomic number and mass number and emits an alpha particle which is a 4He2 nucleus. Beta particle emission in which a radioactive nucleus undergoes a fission reaction producing a new more stable nucleus with higher atomic number and 35 17 79 35 15 7 235 92 1 1 4 2 0 -1 1 0 0 +1

the same mass number and emits a beta particle which is an electron. This occurs as a neutron in the nucleus is converted into a proton and an electron which is expelled from the nucleus as the beta particle. Gamma photon emission in which a radioactive nucleus undergoes a fission reaction producing a more stable nucleus of the same element with the same atomic number and the same mass number and emits high energy electromagnetic radiation (not a particle with mass) which is a gamma photon. Positron emission in which a radioactive nucleus undergoes a fission reaction producing a new more stable nucleus with lower atomic number and the same mass number and emits a beta particle which is an electron. This occurs as a proton in the nucleus is converted into a neutron and a positron which is expelled from the nucleus. Electron capture in which a radioactive nucleus undergoes a fission reaction producing a new more stable nucleus with lower atomic number and the same mass number and emits an X-ray photon. This occurs as the nucleus absorbs one of the atom's inner shell electrons and the captured electron combines with a proton to form a neutron. 10) Balance the following radioactive decay reactions and label each as one of the 5 types. Co → Co + γ Gamma photon emission Be + e → Li Electron Capture Hg → Pt + He Alpha particle emission H → He + e Beta particle emission Al → Mg + e Positron emission 60m 27 60 27 0 0 7 4 0 -1 7 3 180 80 176 78 4 2 3 1 3 2 0 -1 26 13 26 12 0 +1

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11) Transmutation is a process in which a nucleus is bombarded by another nucleus or a nuclear particle causing the reactant nucleus to rearrange to give a new more stable product nucleus or nuclei. 12) Balance the following transmutation reactions. N + He → O + H P → Si + e 13) A cyclotron also called a particle accelerator is a device used to accelerate particles to high speeds to cause highly charged nuclei to collide. 14) A transuranium element is any of the synthetic elements with atomic numbers greater than that of U, the naturally-occurring element of highest atomic number produced by transmutation reactions. 14 7 4 2 17 8 1 1 30 15 30 14 0 +1

6.1_ Nuclear Chemistry_ General Chemistry II w_Lab- 2021- Schiren

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