1. Nuclear Chemistry Chapter 22

2. Notation

3. The Nucleus Remember that the nucleus is comprised of the two nucleons, protons and neutrons. The number of protons is the atomic number. The number of protons and neutrons together is effectively the mass of the atom.

4. Isotopes Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms. There are three naturally occurring isotopes of uranium: –Uranium-234 –Uranium-235 –Uranium-238

5. Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleusNuclear reactions involve the nucleus The nucleus opens, and protons and neutrons are rearrangedThe nucleus opens, and protons and neutrons are rearranged The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energyThe opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy “Normal” Chemical Reactions involve electrons, not protons and neutrons“Normal” Chemical Reactions involve electrons, not protons and neutrons

7. Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934).One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

8. Marie Curie a Pioneer of Radioactivity Winner of 1903 Nobel Prize for Physics with Henri Becquerel and her husband,Pierre Curie. Winner of the sole 1911 Nobel Prize for Chemistry.

9. Rutherford’s Experiment

11. Penetrating Ability

12. Alpha Decay Loss of an  -particle (a helium nucleus) He 4242 U 238 92  Th 234 90 He 4242 +

13. Beta Decay Loss of a  -particle (a high energy electron)  0−10−1 e 0−10−1 or I 131 53 Xe 131 54  + e 0−10−1

14. Positron Emission Loss of a positron (a particle that has the same mass as but opposite charge than an electron) e 0101 C 11 6  B 11 5 + e 0101

15. Gamma Emission Loss of a  -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle)  0000

16. Electron Capture (K-Capture) Addition of an electron to a proton in the nucleus –As a result, a proton is transformed into a neutron. p 1111 + e 0−10−1  n 1010

17. Nuclei with atomic number > 83 are radioactive

18. 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 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

19. 212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po. 4 He 2 44 2 or alpha particle - 212 Po 4 He + A X 84 2Z 212 = 4 + AA = 208 84 = 2 + ZZ = 82 212 Po 4 He + 208 Pb 84 282

20. Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He ? + 1 n 5 2 0

21. Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He 13 N + 1 n 5 2 7 0

22. Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4 He and 11 B. Reactions using neutrons are called  reactions because a  ray is usually emitted. Radioisotopes used in medicine are often made by  reactions.

23. Nuclear Stability Certain numbers of neutrons and protons are extra stable n or p = 2, 8, 20, 50, 82 and 126 Like extra stable numbers of electrons in noble gases (e - = 2, 10, 18, 36, 54 and 86) Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons All isotopes of the elements with atomic numbers higher than 83 are radioactive All isotopes of Tc and Pm are radioactive

24. Half-Life HALF-LIFE is the time that it takes for 1/2 a sample to decompose.HALF-LIFE is the time that it takes for 1/2 a sample to decompose. The rate of a nuclear transformation depends only on the “reactant” concentration.The rate of a nuclear transformation depends only on the “reactant” concentration.

25. Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?

26. Kinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234 After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams

27. Kinetics of Radioactive Decay A daughter rate = - AA tt A = A 0 e (-kt) lnA = lnA 0 - kt A = the amount of atoms at time t A 0 = the amount of atoms at time t = 0 k is the decay constant (sometimes called ) Ln 2 = k t½t½ 0.693 = k t½t½

28. Problem A sample of 3x10 7 Radon atoms are trapped in a basement that is sealed. The half-life of Radon is 3.83 days. How many radon atoms are left after 31 days? answer:1.2x10 5 atoms

29. Ans: Q:

30. Ans:

31. Radiocarbon Dating 14 N + 1 n 14 C + 1 H 716 0 14 C 14 N + 0  + 6 7 t ½ = 5730 years Uranium-238 Dating 238 U 206 Pb + 8 4  + 6 0  92822 t ½ = 4.51 x 10 9 years 23.3

32. Learning Check! Q: The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 31 hours?

33. Nuclear Fission Fission is the splitting of atoms These are usually very large, so that they are not as stable Fission chain has three general steps: 1. Initiation. Reaction of a single atom starts the chain (e.g., 235 U + neutron) 2. Propagation. 236 U fission releases neutrons that initiate other fissions 3. Termination.

34. Nuclear Fission

35. Representation of a fission process.

36. Nuclear Fusion Fusion Excessive heat can not be contained Attempts at “cold” fusion have FAILED. “Hot” fusion is difficult to contain

37. Radioisotopes in Medicine 1 out of every 3 hospital patients will undergo a nuclear medicine procedure 24 Na, t ½ = 14.8 hr,  emitter, blood-flow tracer 131 I, t ½ = 14.8 hr,  emitter, thyroid gland activity 123 I, t ½ = 13.3 hr,  ray emitter, brain imaging 18 F, t ½ = 1.8 hr,   emitter, positron emission tomography 99m Tc, t ½ = 6 hr,  ray emitter, imaging agent Brain images with 123 I-labeled compound

38. Chemistry In Action: Food Irradiation DosageEffect Up to 100 kilorad Inhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables. 100 – 1000 kilorads Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit. 1000 to 10,000 kilorads Sterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning.