1. 1 Ch 26 pp. 756-777 Nuclear Chemistry 1.What distinguishes nuclear and regular chemistry? 2.What is radioactivity, who discovered it, how was it discovered? 3.What are three kinds of ionizing radiation and differences between them? 4.What nuclear isotope symbols exist? 5.How are nuclear reactions balanced? 6.Why is so much energy released in nuclear reactions?

2. 2 Ch 26 Nuclear Chemistry involves the nucleus What distinguishes nuclear and regular chemistry? There are MAJOR differences between nuclear chemistry and the rest of chemistry.

3. 3 Chemical vs. Nuclear Reactions Chemical ReactionsNuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays

4. 4 Chemical vs. Nuclear Reactions Chemical ReactionsNuclear Reactions Occur when bonds are brokenOccur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element

5. 5 Chemical vs. Nuclear Reactions Chemical ReactionsNuclear Reactions Occur when bonds are brokenOccur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons

6. 6 Chemical vs. Nuclear Reactions Chemical ReactionsNuclear Reactions Occur when bonds are brokenOccur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electronsMay involve protons, neutrons, and electrons Involve small energy changes Involve large energy changes from breaking the binding force which holds the nucleus together.

7. 7 Chemical vs. Nuclear Reactions Chemical ReactionsNuclear Reactions Occur when bonds are brokenOccur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electronsMay involve protons, neutrons, and electrons Associated with small energy changesAssociated with large energy changes Reaction rate is influenced by temperature, particle size, concentration, etc. Reaction rate is not influenced by temperature, particle size, concentration, etc.

8. 8 What is radioactivity, who discovered it? Becquerel discovered radiation, it was called radioactivity by Marie Curie, his graduate student.

9. 9 Radioactive Decay Discovered by Antoine Henri Becquerel in 1896 Photographic plates were exposed by uranium salts

10. 10 What are three kinds of ionizing radiation and differences between them? Alpha, beta and gamma radiation. The first two are particles, the last is a ray of energy. They all have loads of energy.

11. 11 Three types of Ionizing Radiation: alpha, beta, gamma Alpha (ά) – a positively charged helium isotope - the charge is often not shown because it involves electrons, not protons and neutrons Alpha (ά) – a positively charged helium isotope - the charge is often not shown because it involves electrons, not protons and neutrons Beta (β) – an electronBeta (β) – an electron Gamma (γ) – pure energy; a wave or ray, not a particleGamma (γ) – pure energy; a wave or ray, not a particle

12. 12 The penetrating power of radiation.  : 0.05 mm body tissue  : 4 mm body tissue  : passes through body tissue.

13. 13 Subatomic Particles and their Symbols Electron Electron NeutronNeutron Positron : a positive electron Positron : a positive electron Proton : usually referred to as hydrogen-1Proton : usually referred to as hydrogen-1 Any element written in isotopic notation i.e.Any element written in isotopic notation i.e.

14. 14 Nuclear Reaction Types Alpha decay: emits an alpha particle. Beta decay: emits a beta particle. Gamma decay: emits a gamma ray. Electron capture: An electron is absorbed. Positron emission: A positron is emitted. Fission: Splitting the nucleus. Fusion: Combining two nuclei together.

15. 15 Nuclear particles (including positively charged protons) are held together by the strong force An even numbers of protons and neutrons are the most stable. An approximately 1-1 neutron to proton ration is generally most stable Atomic number > 83 is never stable. Why some Nuclei are unstable (radioactive):

16. 16 Band of Stability and Radioactive Decay

17. 17 Radioactive elements decay until they become stable nuclei.

18. 18 alpha decay: loss of a helium nucleus.

19. 19 alpha decay ANSWERS

20. 20 beta emission –A neutron splits into a proton and electron which is spit out as a  particle.

21. 21 beta emission ANSWER –A neutron splits into a proton and electron which is spit out as a  particle.

22. 22 positron emission –A proton kicks out positive charge (a positron,  +) to become a neutron. –The positron collides with an electron annihilating both and generating energy

23. 23 electron capture (EC) –an electron (from inner shell) is sucked into the nucleus to combine with a proton – produces a neutron.

24. 24 Gamma Emission Emission of energy as a wave (a photon) from an unstable nucleus.

25. 25 Balancing Nuclear Reactions Atomic numbers and mass numbers must balance for reactants and products. fill in what is missing: 1. Problem Pu-239 (plutonium 239) loses an alpha particle (He nucleus). Write the nuclear reaction 2. Write the nuclear equation for the beta emitter Co-60. 3. What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He  ? + 1 n 5 2 0 5 2 0 5. Into what element is an atom of nitrogen-13 transformed when it emits a positron?

26. 26 Why are such large amounts of energy released in nuclear reactions? Mass Defect Some of the nucleus’ mass can be converted into energy as shown by Einstein’s famous equation:Some of the nucleus’ mass can be converted into energy as shown by Einstein’s famous equation: E=mc 2 Energy Mass defect Speed of light, a really big value: 300,000,000 m/s

27. 27 Energy of Nuclear Reactions 6.1512+ 1.00782 ≠ 3.01603 + 4.00260 7.02294 ≠ 7.01863.

28. 28 The world’s first atomic explosion, July 16, 1945 at Alamogordo, New Mexico. Fission: splitting the atom. Used in atomic bombs and nuclear power plants. Not every atom can be split. Those that can be are massive elements.

29. 29 Fission requires a chain reaction to keep going.

30. 30 Nuclear Power Plants require fuel with ~3% fissionable material, Nuclear bombs require ~90% fissionable material. Very difficult to concentrate fissionable material.

31. 31 Controlled nuclear fission involves: A core containing fuel rods, control rods and a cooling system all surrounded by a containment structure. fuel rods contain ~ 3% fissionable uranium 235 in pellets fit into tubes. control rods which can absorb neutrons (such as the element boron). A containment structure to shield the outside from harmful radiation. A cooling system to prevent the core from overheating and melting down.

32. 32 Schematic diagram of a nuclear power plant.

33. 33 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.

34. 34 Fusion powers the sun and stars. Not ready for use in commercial nuclear power plants. In Fusion small nuclei Combine and release lots of energy. 2 H + 3 H 4 He + 1 n + 1 1 2 0 1 1 2 0 Energy

35. 35 Half Life is the time required for half of a radioisotope’s nuclei to decay into its products. Half Life is the time required for half of a radioisotope’s nuclei to decay into its products. # of ½ lives % Remai ning 0100% 150% 225% 312.5% 46.25% 53.125% 61.5625 %

36. 36Half-Life The rate of nuclear decay can not be sped up or slowed down.The rate of nuclear decay can not be sped up or slowed down. Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?

37. 37 For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years? For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years? You can use an equation or a table to solve: Where m t is the mass remaining at time t m o is the initial mass of the isotope. n= number of half lives. # of ½ livesTime (Years) Amount Remaining (g) 0010 1295 2582.5 3871.25 41160.625

38. 38 Half Life Problems, first set 1.The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours? 2.If a radioactive isotope has a ½ life of 20 minutes, what percent of the sample will remain after 1 hour? 3.If 75% of a sample decays after 6 hours, what is its half life? 4.If a radioisotope has a half-life of 2 weeks, how long will it take for 99% of the sample to decay?

39. 39 Example 1: If gallium – 68 has a half-life of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ____ 2 half lives? ______ 3 half lives? _______ Example 2: Cobalt – 60, with a half-life of 5 years, is used in cancer radiation treatments. If a hospital purchases a supply of 30.0 g, how much would be left after 15 years? ______________ Example 3: Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days? ______________ Example 4: The half-life of polonium-218 is 3.0 minutes. If you start with 20.0 g, how long will it take before only 1.25 g remains? ______________ Example 5: A sample initially contains 150.0 mg of radon-222. After 11.4 days, the sample contains 18.75 mg of radon-222. Calculate the half-life. Half Life Problems, 2nd set:

40. 40 Applications – Carbon Dating nitrogen in the atmosphere is bombarded by neutrons to form 14 Cnitrogen in the atmosphere is bombarded by neutrons to form 14 C This carbon is integrated into CO 2 which then enters the food chainThis carbon is integrated into CO 2 which then enters the food chain

41. 41 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.

42. 42 Is radiation natural? Is radiation natural? What are the effects of Radiation? What are the effects of Radiation? Besides bombs and nuclear power plant producing electricity, what is nuclear chemistry good for? Besides bombs and nuclear power plant producing electricity, what is nuclear chemistry good for? Some additional topics to cover:

43. 43

44. 44 Effects of Radiation

45. 45 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.

46. 46 Medical diagnosis and treatment Radiation treats cancer by killing rapidly dividing cells (cancerous cells) quicker than healthy cells.Radiation treats cancer by killing rapidly dividing cells (cancerous cells) quicker than healthy cells. Exposure is a greater risk for infants, babies, teens …people full of normal cells already rapidly dividing in these growing people.Exposure is a greater risk for infants, babies, teens …people full of normal cells already rapidly dividing in these growing people.