Nuclear Chemistry Chapter 23 23.1-23.6. Nuclear Chemistry Nuclear Chemistry- the study of reactions involving changes in atomic nuclei. Importance Disadvantages.
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- Nuclear Chemistry Chapter 23 23.1-23.6
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- Nuclear Chemistry Nuclear Chemistry- the study of reactions involving changes in atomic nuclei. Importance Disadvantages
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- Nuclear Reactions Except for Hydrogen, all nuclei contain particles called protons and neutrons. Nuclei can be stable or unstable. Unstable Nuclei emit particles and/or electromagnetic radiation spontaneously. Phenomenon is called Radioactivity. Nuclear Transmutation- results from the bombardment of nuclei by neutrons, protons or other nuclei.
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- Nuclear Reactions Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons X A Z Mass Number Atomic Number Element Symbol
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- Nuclear Reactions 1p1p 1 1H1H 1 or proton 1n1n 0 neutron 0e0e 00 or electron 0e0e +1 00 or positron 4 He 2 44 2 or particle
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- Balancing Nuclear Equations 1.Conserve mass number (A). The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 1n1n 0 U 235 92 + Cs 138 55 Rb 96 37 1n1n 0 ++ 2 235 + 1 = 138 + 96 + 2x1
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- Balancing Nuclear Equations 2.Conserve atomic number (Z) or nuclear charge. The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants. 1n1n 0 U 235 92 + Cs 138 55 Rb 96 37 1n1n 0 ++ 2 92 + 0 = 55 + 37 + 2x0
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- Balancing Nuclear Equations 212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po. 4 He 2 44 2 or alpha particle - 212 Po 4 He + A X 84 2Z 212 = 4 + AA = 208 84 = 2 + Z Z = 82 212 Po 4 He + 208 Pb 84 282 23.1
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- Chemical Reactions vs. Nuclear Reactions
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- Nuclear Stability Nucleus is very small Contributes most of weight of atom Extremely high density Even higher # of particles
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- Nuclear Stability Particles repel/attract each other neutron-to-proton ratio Predicting stability: Magic numbers: 2,8,20,50,82,126 Even numbers of neutrons and protons vs. odd numbers All isotopes of elements with atomic numbers higher than 83 are radioactive. All isotopes of Tc and Pm are radioactive.
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- n/p too large beta decay X n/p too small positron decay or electron capture Y
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- Nuclear Stability Beta decay 14 C 14 N + 0 + 6 7 40 K 40 Ca + 0 + 19 20 1 n 1 p + 0 + 0 1 Decrease # of neutrons by 1 Increase # of protons by 1 23.2
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- Nuclear Stability and have A = 0 and Z = 0 1 p 1 n + 0 + 1 0 +1 Positron decay 11 C 11 B + 0 + 6 5 +1 Increase # of neutrons by 1 38 K 38 Ar + 0 + 19 18 +1 Decrease # of protons by 1
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- Nuclear Stability Electron capture decay 37 Ar + 0 e 37 Cl + 18 17 Increase # of neutrons by 1 55 Fe + 0 e 55 Mn + 26 25 Decrease # of protons by 1 1 p + 0 e 1 n + 1 0
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- Nuclear Stability Alpha decay 212 Po 4 He + 208 Pb 84 282 Decrease # of neutrons by 2 Decrease # of protons by 2
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- Nuclear Binding Energy Nuclear Binding Energy- the energy required to break up a nucleus into its component protons and neutrons. Necessity? Mass Defect Einsteins Theory of Relativity E = mc 2
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- Nuclear Binding Energy BE + 19 F 9 1 p + 10 1 n 9 1 0 BE = 9 x (p mass) + 10 x (n mass) 19 F mass E = mc 2 BE (amu) = [(9 x 1.007825) + (10 x 1.008665)] 18.9984 BE = 0.1587 amu 1 amu = 1.49 x 10 -10 J BE = 2.37 x 10 -11 J
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- Nuclear Binding Energy binding energy per nucleon = binding energy number of nucleons = 2.37 x 10 -11 J 19 nucleons = 1.25 x 10 -12 J
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- Nuclear Binding Energy
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- Natural Radioactivity Outside the belt of stability, nuclei are radioactive. Radioactive nuclei spontaneously emit radiation. particles, particles, rays, etc. Disintegration of radioactive nucleus leads to a decay series.
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- Radioactive Decay--Dating Uranium decay After time, half of parent exsists Equal amounts of parent and daughter Age?
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- Nuclear Transmutations Rutherford, 1919 Artificial Radioactivity Nitrogen bombarded by particles 14 N + 4 17 O + 1 p 7 2 8 1
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- Nuclear Transmutation Notation for reactions First Isotope (bombarding particle, ejected particle) Final Isotope Notation for Nitrogen-14 bombarded with particle.
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- Transuranium Elements Synthetic elements Atomic Numbers greater than 92 Particle Accelerator necessary for preparation
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- Particle Accelerator Cyclotron Particle Accelerator
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- Nuclear Fission Nuclear Fission- the process in which a heavy nucleus (mass number > 200) divides to form smaller nuclei of intermediate mass and one or more neutrons. Energy is released. Uranium-235 was the first element discovered to go through nuclear fission.
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- Nuclear Fission 235 U + 1 n 90 Sr + 143 Xe + 3 1 n + Energy 92 54 3800
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- Nuclear Fission Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions. The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass.
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- Non-critical Critical Chain Reaction
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- The Atomic Bomb
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- Nuclear Reactors Peaceful application of nuclear fission Generates electricity from chain reactions Provides 20% of electricity in U.S. Light water reactors; Heavy water reactors; Breeder reactors
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- Light Water Reactors Most U.S. nuclear reactors are light water Light Hydrogen Use Uranium-235 under controlled conditions Releases large quantities of steam Steam drives electric generators Needs large amounts of coolant Plants built by lakes and rivers Large amounts of thermal pollutant
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- Light Water Reactors
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- Heavy Water Reactors Uses Deuterium D 2 O D absorbs neutrons less efficiently than H Does not require U-235 Neutrons leak out of reactor Expensive to prepare D 2 O Environmentally friendly
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- Breeder Reactors Breeder Reactor- uses uranium fuel, but unlike a conventional nuclear reactor, it produces more fissionable materials than it uses. Converts uranium-238 to plutonium-239 in a 3 step process. Plutonium-239 undergoes fission Reactor produces 1 mole of p-239 for every 1 mole used. Takes 7-10 years for complete regeneration.
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- Hazards of Nuclear Energy Production of radioactive isotopes with long half-lives (24,400 years) Radioactive and toxic substances Three-mile Island Reactor- radiation escaped Chernobyl Nuclear Plant- fire and explosion Accidents Waste Disposal
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- Nuclear Fusion Nuclear Fusion- the combining of small nuclei into larger ones. Two small nuclei can combine and release large amounts of energy To occur, the nuclei must be in an environment with high temperature. Thermonuclear Reactions Nuclear fusion occurs constantly on the Sun.
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- Nuclear Fusion How do we get it to occur? Container?
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- The Hydrogen Bomb Thermonuclear Bomb All power and no control Fusion reaction then fission reaction Fusion reaction creates high temp. for fission reaction Bombs usually contain Co-59 and upon explosion convert to Co-60
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