Nuclear Chemistry

1. Nuclear Chemistry Chapter 10

2. Alpha, Beta, and Gamma Rays • Radioactive elements emit three types of radiation • Alpha • Beta • Gamma Rays

3. Alpha particles • Alpha particles carry a positive two charge and are composed of 2 protons and 2 neutrons. • When an alpha particle is emitted, the atomic mass will decrease by 4 AMU’s. • The atomic # will decrease by 2.

4. Beta particles • Beta particles carry a negative charge and are high speed electrons. • When a beta particle is emitted the atomic mass will not change. • The atomic # will increase by 1.

5. Gamma Rays • Gamma radiation has no charge and is made of electromagnetic energy. • When a gamma radiation is emitted the atomic mass will not change. • The atomic # will not change.

6. Penetrating Powers of Nuclear Radiation Figure 4 Page 294 Gamma radiation is extremely dangerous--a thousand times more potent than x-rays. They will penetrate several centimeters of solid lead. Paper or clothing will block alpha particles Beta particles require a few sheets of aluminum foil. Alpha particlesare 8,000 times as heavy as beta particles.

7. End Monday See Page 295 in Text.

8. Carbon-14 Production • A free neutron enters nucleus and kicks out a proton. Nitrogen transmutates into carbon14.0n1  +  7N14 --------->  6C14  + 1p1

9. Carbon-14 Decays by Beta Emission • The beta particle is ejected from the nucleus. • The nucleon count (atomic mass) is conserved. • The atomic number increases by 1. • Carbon14 transmutates into Nitrogen.

10. U-238 Decay

11. 10.2 Rates of Nuclear Decay

12. Section 10.2 Interest Grabber Analogy for Half-Life The diagrams below represent the charge level of a battery in a robotic dog at different times during the day. You charged the battery so that it was at its highest level at 9:00 A.M. Examine the diagrams, and then answer the questions that follow.

13. Section 10.2 Interest Grabber 1.The dog uses half of any remaining charge every 2 hours. So, if the battery is fully charged at 9:00 A.M., then the charge level will be half at 11:00 A.M., two hours later. If it uses half of the remaining charge another two hours later, what will the energy level be at 1:00 P.M.? • ¼

14. Section 10.2 Interest Grabber 2. Given the same trend, what time is it when the battery’s charge is at the level shown in the last diagram? • 3:00 P.M.

15. Section 10.2 Interest Grabber 3.The battery must be recharged when its charge level reaches half of the level shown in the last diagram. What time will the battery need to be recharged? 5:00 P.M.

16. Half-Life • The half-life of a radioactive sample is average the amount of time required for half of the sample to disintegrate (decay, disappear, transmute). • Half-lives are remarkably constant and not affected by external conditions.

17. Figure 7 Nuclear Decay of Iodine-131 8.07 days 16.14 days 24.21 days

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

19. Half-Life  • A particular nucleus has a half life of 5 years. • If there are 1000 nuclei now, how many will there be in 5 years?   • In 10 years, 15 years? • Five years: 500 nuclei. • Ten years: 250 nuclei. • 15 Years:125 nuclei.

20. 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 daysIf 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

21. Carbon-14 Dating • The longer anything is dead, the less carbon 14 it will have in it. • The half-life of carbon-14 is 5730 years. • 1 Half life is 5730 years = ½ • 2 Half life is 11460 years = ¼ • 3 Half life is 17190 years = 1/8 • 4 Half life is 22920 years = 1/16 • 5 Half life is 28650 years = 1/32 • Can only be use to date objects less than 50,000 years old.

22. Measuring the Age of Organic Matter • A German tourist in the Italian Alps discovered the remains of the "Iceman" in the ice of a glacier in 1991.

23. The current activity per gram of carbon is half of what it would be if the Iceman were alive. Since the half-life of carbon-14 is about 5730 years, theIceman's remains are about 5730 years old. Calculating the Iceman's Age

24. The dating of older but nonliving things. Rocks and minerals Uranium-238 decays with a half-life of 4.5 billion years, with an end-product oflead-206. By measuring  the lead-206 content, the age of rocks may be determined. Uranium Dating

25. Section 10.3 Interest Grabber Introduction to Transmutation Examine the diagram below that represents the nuclei of isotopes in a nuclear reaction, and answer the questions that follow. In the diagram, the light circles represent protons, and the dark circles represent neutrons. 1. What isotopes are represented by the starting nuclei? 2. What isotope is represented by the larger nucleus that is produced in the nuclear reaction? 3. What other particle is produced?

26. Section 10.3 Reading Strategy Monitoring Your Understanding Possible answers may include: • Examples of artificial transmutation • Rutheford’s transmutation of nitrogen-14 into oxygen-17; the synthesis of neptunium-239 • Uses of transuranium elements • Smoke detectors (americium-241); space probes (plutonium-238)

27. Natural Transmutation of Elements • One nucleus changing into another. • Total number of nucleons is conserved: • 238 =====> 234 + 4 • Total charge is conserved: • 92 =====> 90 + 2

28. Natural Transmutation of Elements • One nucleus changing into another. • Total number of nucleons is conserved: • 234 =====> 234 + e- • Total charge is increased by 1: • 90 =====> 91

29. Artificial Transmutation of Elements • Ernest Rutherford was the first to cause transmutation in the lab. • The impact of an alpha particle on a nitrogen nucleus causes transmutation.

30. Reading Strategy Comparing and Contrasting a. is the splitting of a large nucleus into two smaller fragments b. is widely used as an alternative energy source c. is the fusing of two small nuclei into one larger nucleus d. is still being researched and developed as an alternativeenergy source

31. Figure 15 Comparing Strong Nuclear Forces and Electrical Forces

32. Figure 15 Comparing Strong Nuclear Forces and Electrical Forces

33. Figure 15 Comparing Strong Nuclear Forces and Electrical Forces

34. Figure 15 Comparing Strong Nuclear Forces and Electrical Forces

35. Figure 16 Effect of Nuclear Size on Nuclear and Electrical Forces

36. Figure 18 Nuclear Fission of Uranium-235

37. Figure 19 Chain Reaction of Uranium-235

38. The Nucleus • The nucleus is made of smaller subatomic particles called nucleons or (protons and neutrons). • The nucleus has a positive net charge. • When an alpha particle leave they have a violent electrical repulsion. • Nucleons are 2000 times more massive than an electron.

39. Unstable Nuclei • Neutrons 1-4 provide strong forces of attraction for the indicated proton, but other neutrons are too far away to help balance the longer- range forces of repulsion provided by the many protons to the right of the proton. • The larger the nucleus, the more unstable it is.

40. Reaching Stability Through Gamma Ray Emission • Nuclei with excess energy emit gamma rays to gain stability.

41. Nuclear Fission • The splitting of the nucleus of a heavy atom. • There is 100,000,000 times more energy released from fission than when coal is burned.

42. A chain reaction • A chain reaction occurs if more than one neutron goes on to cause another fission. • One pound of U-235, ifcompletely fissioned, yields the same energy as 100,000,000 pounds of coal.

43. Cadmium Control Rods Absorb Neutrons • Cadmium is a good absorber of neutrons.

44.  A Nuclear Reactor • Heat generated by fission in uranium rods creates steam which turns turbineblades connected to a coil of wire in magnetic field.

45. Mass is Energy and Energy is Mass • The work done per nucleon adds energy to each nucleon, which appears as increasedmass. • Nucleons broken out of the nucleus weigh more outside than they do inside.

46. Fusion • Fusion is the opposite of fission. • Energy in the sun come from hydrogen fusion. • Deuterium (hydrogen 2) must be moving extremely fast to fuse.

47. Fusion in Stars • The extreme 10 million degrees at the core of the sun causes fusion of hydrogen into helium.

48. Mass is energy: E = mc2Energy is mass:  m = E /c2 Albert Einstein         (1879-1955) Albert Einstein and Mass-Energy Equivalence • When a uranium nucleus splits, the mass of the remnants is less than the original mass. The difference appears as light, heat, and kinetic energy.