2. Nuclear Chemistry

3. Radioactivity Antoine Henri Becquerel (1852-1908) Discovered radioactivity accidentally while experimenting with photographic film.

4. Radioactivity Discovered polonium and radiumDiscovered polonium and radium Coined the term “radioactivity”Coined the term “radioactivity” Marie Curie (1867-1934)

5. Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve changes in the nucleusNuclear reactions involve changes in the nucleus The splitting of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energyThe splitting of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy “Normal” Chemical Reactions involve electrons, not the nucleus“Normal” Chemical Reactions involve electrons, not the nucleus

6. Types of Radiation Alpha (ά) – a positively charged helium isotope Alpha (ά) – a positively charged helium isotope Beta (β) – an electronBeta (β) – an electron Gamma (γ) – pure energy; called a ray rather than a particleGamma (γ) – pure energy; called a ray rather than a particle

7. Other Nuclear Particles Neutron Neutron Positron – a positive electron Positron – a positive electron

8. Penetrating Ability

9. X A Z Mass Number Atomic Number Element Symbol Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons A Z 1n1n 0 neutron 0e0e 00 or Beta particle 0e0e +1 positron 4 He 2 44 2 or alpha particle 1 0 0 0 +1 4 2 Symbol Format

10. Balancing Nuclear Reactions The reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) Atomic numbers must balance and Mass numbers must balance

11. Balancing Nuclear Equations 1.Conserve mass number (A). 1n1n 0 U 235 92 + Cs 138 55 Rb 96 37 1n1n 0 ++ 2 (235 + 1) = 236 (138 + 96 + 2x1) = 236 2.Conserve atomic number (Z) or nuclear charge. 1n1n 0 U 235 92 + Cs 138 55 Rb 96 37 1n1n 0 ++ 2 92 + 0 = 55 + 37 + 2x0 23.1

12. Nuclear Reactions Alpha emissionAlpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. 226  ? + 222 88 86 Rn Ra

13. 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 23.1

14. Nuclear Reactions Beta emissionBeta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1. 238  ? + 238 9293 UNp 238  0+ 238 92-193 UNp 

15. Other Types of Nuclear Reactions Positron ( 0 +1  ): a positive electron Electron capture: Electron capture: the capture of an electron 207

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

17. 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

18. Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60. 60 Co 0 e+ 60 Ni 27 -128

19. 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

20. Artificial Nuclear Reactions Example of a  reaction is production of radioactive 31 P for use in studies of P uptake in the body. 31 15 P + 1 0 n ---> 32 15 P + 

21. Transuranium Elements Elements beyond 92 (transuranium) made by starting with a  reaction 238 92 U + 1 0 n ---> 239 92 U +  239 92 U ---> 239 93 Np + 0 -1  239 93 Np ---> 239 94 Pu + 0 -1  239 93 Np ---> 239 94 Pu + 0 -1 

22. 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.

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

24. 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

25. Radiocarbon Dating Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation 14 N + 1 o n ---> 14 C + 1 H The C-14 is oxidized to CO 2, which circulates through the biosphere. When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t 1/2 = 5730 years. Activity of a sample can be used to date the sample.

26. Geiger Counter Used to detect radioactive substances

27. Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours? 39 hr./13 hr. = 3 half lives 64g x ½ = 32g x ½ = 16g x ½ = 8g will be left after 3 half lives. 0R 64/8 = 8 grams

28. Nuclear Fission

29. Representation of a fission process.

30. Nuclear Fission & POWER Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. 17% of the world’s energy comes from nuclear.17% of the world’s energy comes from nuclear.

31. Figure 19.6: Diagram of a nuclear power plant.

32. Nuclear Fusion Fusion small nuclei combine 2 H + 3 H 4 He + 1 n + 1 1 2 0 Occurs in the sun and other stars Energy

33. Effects of Radiation

34. Band of Stability and Radioactive Decay

36. Nuclear Medicine: Imaging Thyroid imaging using Tc-99m

37. Food Irradiation Food can be irradiated with  rays from 60 Co or 137 Cs.Food can be irradiated with  rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration.Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs.USDA has approved irradiation of meats and eggs.