Nuclear Chemistry

1. Nuclear Chemistry Chapter 23 23.1-23.6

2. Nuclear Chemistry • Nuclear Chemistry- the study of reactions involving changes in atomic nuclei. • Importance • Disadvantages

3. 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.

4. A X Mass Number Element Symbol Z Atomic Number 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

5. Nuclear Reactions a particle proton neutron electron positron or or 1H 1p 0b 0e or 1 1 +1 1n 0e +1 0b 0 -1 -1 4a 4He or 2 2

6. Balancing Nuclear Equations + + + 2 1n 1n 96 0 0 Rb 37 235 138 Cs U 92 55 • Conserve mass number (A). The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 235 + 1 = 138 + 96 + 2x1

7. Balancing Nuclear Equations + + + 2 1n 1n 96 0 0 Rb 37 235 138 Cs U 92 55 • 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. 92 + 0 = 55 + 37 + 2x0

8. Balancing Nuclear Equations or alpha particle - 212Po 4He + AX 2 Z 84 212Po 4He + 208Pb 2 82 84 4a 4He 2 2 212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po. 212 = 4 + A A = 208 Z = 82 84 = 2 + Z 23.1

10. Chemical Reactions vs. Nuclear Reactions

11. Nuclear Stability • Nucleus is very small • Contributes most of weight of atom • Extremely high density • Even higher # of particles

12. 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.

13. X Y n/p too large beta decay n/p too small positron decay or electron capture

14. Nuclear Stability 14C 14N + 0b + n 6 7 -1 40K 40Ca + 0b + n 19 20 -1 1n 1p + 0b + n 0 1 -1 Beta decay Decrease # of neutrons by 1 Increase # of protons by 1 23.2

15. Nuclear Stability 11C 11B + 0b + n 6 5 +1 38K 38Ar + 0b + n 19 18 +1 1p 1n + 0b + n 1 0 +1 n and n have A = 0 and Z = 0 Positron decay Increase # of neutrons by 1 Decrease # of protons by 1

16. Nuclear Stability 37Ar + 0e 37Cl + n 18 17 -1 55Fe + 0e 55Mn + n 26 25 -1 1p + 0e 1n + n 1 0 -1 Electron capture decay Increase # of neutrons by 1 Decrease # of protons by 1

17. Nuclear Stability 212Po 4He + 208Pb 2 82 84 Alpha decay Decrease # of neutrons by 2 Decrease # of protons by 2

18. Nuclear Binding Energy • Nuclear Binding Energy- the energy required to break up a nucleus into its component protons and neutrons. • Necessity? • Mass Defect • Einstein’s Theory of Relativity E = mc2

19. Nuclear Binding Energy BE + 19F 91p + 101n 0 9 1 E = mc2 BE = 9 x (p mass) + 10 x (n mass) – 19F mass 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 10-11J

20. 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

21. Nuclear Binding Energy

24. Natural Radioactivity • Outside the belt of stability, nuclei are radioactive. • Radioactive nuclei spontaneously emit radiation. • α particles, β particles, γ rays, etc. • Disintegration of radioactive nucleus leads to a decay series.

26. Radioactive Decay--Dating • Uranium decay • After time, half of parent exsists • Equal amounts of parent and daughter • Age?

27. 14N + 4a17O + 1p 7 2 1 8 Nuclear Transmutations • Rutherford, 1919 • Artificial Radioactivity • Nitrogen bombarded by α particles

28. Nuclear Transmutation • Notation for reactions • First Isotope (bombarding particle, ejected particle) Final Isotope • Notation for Nitrogen-14 bombarded with a particle.

30. Transuranium Elements • Synthetic elements • Atomic Numbers greater than 92 • Particle Accelerator necessary for preparation

31. Cyclotron Particle Accelerator Particle Accelerator

32. 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.

33. 235U + 1n 90Sr + 143Xe + 31n + Energy 0 38 0 54 92 Nuclear Fission

34. 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.

35. Chain Reaction Non-critical Critical

36. The Atomic Bomb

37. 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

38. 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

39. Light Water Reactors

40. Heavy Water Reactors • Uses Deuterium D2O • D absorbs neutrons less efficiently than H • Does not require U-235 • Neutrons leak out of reactor • Expensive to prepare D2O • Environmentally friendly

41. 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.

42. 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

43. 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.

44. Nuclear Fusion • How do we get it to occur? • Container?

45. 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