Nuclear Chemistry

1. Nuclear Chemistry Unit 2.5

2. Introduction to Nuclear Chemistry • Nuclear chemistry is the study of the structure of and the they undergo. atomic nuclei changes

3. Chemical vs. Nuclear Reactions

4. Chemical vs. Nuclear Reactions

5. Chemical vs. Nuclear Reactions

6. Chemical vs. Nuclear Reactions

7. Chemical vs. Nuclear Reactions

8. The Discovery of Radioactivity (1895 – 1898): Roentgen • found that invisible rays were emitted when electrons hit the surface of a fluorosent screen (discovered x-rays) • Becquerel accidently discovered that phosphorescent rock produced spots on photographic plates uranium

9. The Discovery of Radioactivity (1895 – 1898): Marie and Pierre Curie • isolated the components ( atoms) emitting the rays • – process by which atoms give off • – the penetrating rays and particles by a radioactive source uranium Radioactivity rays or particles Radiation emitted

10. The Discovery of Radioactivity (1895 – 1898): • identified 2 new elements, and on the basis of their radioactivity • These findings Dalton’s theory of indivisible atoms. Marie Curie, continued polonium radium contradicted

11. The Discovery of Radioactivity (1895 – 1898): Isotopes • – atoms of the same element with different numbers of • – isotopes of atoms with unstable nuclei (too many or too few neutrons) • – when unstable nuclei lose energy by emitting to become more neutrons Radioisotopes Radioactive decay radiation stable Spontaneous Reaction!

12. Alpha radiation • Composition – Alpha particles, same as helium nuclei • Symbol – Helium nuclei, He, α • Charge – 2+ • Mass (amu) – 4 • Approximate energy – 5 MeV • Penetrating power – low (0.05 mm body tissue) • Shielding – paper, clothing 4 2

13. Beta radiation • Composition – Beta particles, same as an electron • Symbol – e-, 0-1β • Charge – 1- • Mass (amu) – 1/1837 (practically 0) • Approximate energy – 0.05 – 1 MeV • Penetrating power – moderate (4 mm body tissue) • Shielding – metal foil

14. Gamma radiation • Composition – High-energy electromagnetic radiation • Symbol – ooγ • Charge – 0 • Mass (amu) – 0 • Approximate energy – 1 MeV • Penetrating power – high (penetrates body easily) • Shielding – lead, concrete

15. Review of Atomic Structure

16. Review of Atomic Structure

17. Review of Atomic Structure

18. Review of Atomic Structure

19. Chemical Symbols A chemical symbol looks like… p+ = e- = atomic # To find the number of , subtract the from the mass # 14 C atomic # 6 neutrons mass # atomic #

20. Nuclear Stability not • Isotope is completely stable if the nucleus will spontaneously . • Elements with atomic #s to are . • ratio of protons:neutrons ( ) • Example: Carbon – 12 has protons and neutrons decompose 1 20 very stable p+:n0 1:1 6 6

21. Nuclear Stability 21 83 • Elements with atomic #s to are . • ratio of protons:neutrons (p+ : n0) • Example: Mercury – 200 has protons and neutrons marginally stable 1:1.5 80 120

22. Nuclear Stability unstable > 83 • Elements with atomic #s are and . • Examples: and radioactive Uranium Plutonium

23. Alpha Decay α • Alpha decay – emission of an alpha particle ( ), denoted by the symbol , because an α has 2 protons and 2 neutrons, just like the He nucleus. Charge is because of the 2 . • Alpha decay causes the number to decrease by and the number to decrease by . • determines the element. All nuclear equations are . He 4 2 protons +2 mass 4 atomic 2 Atomic number balanced

24. Alpha Decay • Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission. Step 4: Determine the other product (ensuring everything is balanced). Step 3: Write the alpha particle. Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 210 4 206 He Po Pb 84 2 82 Atomic #

25. Alpha Decay • Example 2: Write the nuclear equation for the radioactive decay of radium – 226 by alpha emission. Step 4: Determine the other product (ensuring everything is balanced). Step 3: Write the alpha particle. Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 226 4 222 He Ra Rn 88 2 86 Atomic #

26. Beta decay β • Beta decay – emission of a beta particle ( ), a fast moving , denoted by the symbol or . β has insignificant mass ( ) and the charge is because it’s an . • Beta decay causes change in number and causes the number to increase by . • A neutron is converted to a proton and a beta particle. electron e- e 0 0 -1 electron -1 no mass atomic 1

27. Beta Decay • Example 1: Write the nuclear equation for the radioactive decay of carbon – 14 by beta emission. Step 4: Determine the other product (ensuring everything is balanced). Step 3: Write the beta particle. Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # e 14 0 14 C N -1 6 7 Atomic #

28. Beta Decay • Example 2: Write the nuclear equation for the radioactive decay of zirconium – 97 by beta decay. Step 4: Determine the other product (ensuring everything is balanced). Step 3: Write the beta particle. Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # e 0 97 97 Zr Nb -1 40 41 Atomic #

29. Gamma decay electromagnetic • Gamma rays – high-energy radiation, denoted by the symbol . • γ has no mass ( ) and no charge ( ). Thus, it causes change in or numbers. Gamma rays almost accompany alpha and beta radiation. However, since there is effect on mass number or atomic number, they are usually from nuclear equations. γ 0 0 no mass atomic always no omitted

30. Transmutation Transmutation the of an atom of one element to an atom of a different element. Radioactive decay is one way that this occurs! conversion

31. Review 4 2 0 -1

32. Half-Life half Half-life time • is the required for of a radioisotope’s nuclei to decay into its products. • For any radioisotope,

33. Half-Life

34. Half-Life • 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 a table:

35. Half-Life • Or an equation! initial mass mt = m0 x (0.5)n mass remaining # of half-lives

36. Half-Life • 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? __________

37. Half-Life • 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? ______________

38. Half-Life • 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? ______________

39. Half-Life • 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? ______________

40. Half-Life • 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.

41. Nuclear Reactions • Characteristics: • Isotopes of one element are into isotopes of another element • Contents of the change • amounts of are released changed nucleus energy Large

42. Types of Nuclear Reactions • decay – alpha and beta particles and gamma ray emission • Nuclear - emission of a or Radioactive disintegration proton neutron

43. Nuclear Fission Fission splitting • - of a nucleus • - Very heavy nucleus is split into approximately fragments • - reaction releases several neutrons which more nuclei • - If controlled, energy is released (like in ) Reaction control depends on reducing the of the neutrons (increases the reaction rate) and extra neutrons ( creases the reaction rate). two equal Chain split slowly nuclear reactors speed absorbing de

44. Nuclear Fission • - 1st controlled nuclear reaction in December 1942. 1st uncontrolled nuclear explosion occurred July 1945. • - Examples – atomic bomb, current nuclear power plants

45. Nuclear Fission • Disadvantages • Produces high level radioactive waste that must be stored for 10,000’s of years. • Meltdown causes disasters like in Japan and Chernobyl. • Advantages • Zero air pollution • Not a fossil fuel so doesn’t contribute to climate change

46. Nuclear Fusion • - Fusion: Combining of two nuclei • - Two light nuclei combine to form a single heavier nucleus • - Does not occur under standard conditions (positive nuclei repel each other) • - Advantages compared to fission – No radioactive waste, inexpensive , • - Disadvantages - requires large amount of energy to start, difficult to control. • - Examples – energy output of stars, hydrogen bomb, future nuclear power plants

47. Uses of Radiation • Radioactive dating: Carbon–14 used to determine the age of an object that was once alive. • Detection of diseases: Iodine–131 used to detect thyroid problems, technetium–99 used to detect cancerous tumors and brain disorders, phosphorus – 32 used to detect stomach cancer. • Treatment of some malignant tumors (cobalt–60 and cesium–137) cancer cells are more sensitive to radiation than normal, healthy cells

48. Uses of Radiation • X-rays • Radioactive tracers: used in research to tag chemicals to follow in living organisms • Everyday items: thorium–232 used in lantern mantels, plutonium–238 used in long-lasting batteries for space, and americium–241 in smoke detectors.