Magnet Chemistry- Unit 2 Nuclear Chemistry ‘New’ book: Ch 2 and Ch 19

1. Magnet Chemistry- Unit 2NuclearChemistry‘New’ book: Ch 2 and Ch 19

2. Nuclear Reactions • Chemical reactions • What can NOT change in a chemical reaction? • Nuclear Reactions: changes that occur in the nucleus of an atom • The nucleus is unstable!! • Most atoms have unstable nuclei.

3. Why are some stable, while others are not? • Primary Reason: • ratio of the neutrons to the protons (n/p) • An atom is most stable when ratio is 1:1 • The maximum ratio of stability is around 1.5 : 1

4. Radioactivity • An unstable nucleus emits rays and particles, called radiation, to become stable • The process is called radioactivity • Gain stability by LOSING energy • Discovery dealt a deathblow to Dalton’s theory of indivisible atoms

5. Primary Types of Radiationhttp://edtech2.boisestate.edu/lindabennett1/502/Nuclear%20Chemistry/types%20of%20decay.html • Alpha particle () • helium nucleus paper 2+ • Beta particle (-) • electron 1- • Gamma () • high-energy photon lead 0 *NOTE: 2 more types, positron and e- capture will be discussed later

6. Radioactivity

7. Recommended Videos • http://www.kentchemistry.com/links/Nuclear/AlphaBetaGamma.htm • https://www.youtube.com/watch?v=oFdR_yMKOCw

8. Radioactive Particles • 1. Alpha Particle (+) • It travels about 1/10 the speed of light (slowest) • It is the largest, most massive particle • It is the most dangerous if ingested • It has the least penetrating ability - paper can stop this particle • *If atom emits A particle (He nucleus), atomic # goes down by 2. (ex: #24 Cr would become #22 Ti)

9. Alpha con’t • Alpha Radiation/Decay: alpha particle • During Alpha decay an atom spits out two protons and two neutrons from its nucleus. This little bundle is called an "alpha particle." • Alpha decay usually happens in larger, heavier atoms. • The symbol looks like Helium because Helium-4 has the same number of protons and neutrons as an alpha particle (no electrons, though). • Since Alpha particles have two protons and no electrons, they have a net charge of 2+. • During Alpha radiation an atom's proton count drops by two, and we know what that means - a NEW element is formed! • Alpha radiation can be stopped by PAPER.

10. Radioactive Particles • 2. Beta Particle (-) • Fast accelerated electron • Ejected when a neutron is converted to a proton in the nucleus • Travels 1/4 the speed of light. • It is lighter and faster than the alpha particle. • Average penetrating ability - can be stopped by heavy clothing, wood, Al

11. Beta con’t • Beta Radiation/Decay  • Think of a neutron as a proton + electron. In beta decay a neutron sends its electron packing, literally ejecting it from the nucleus at high speed. The result? That neutron turns into a proton! • During Beta radiation an atom's proton count goes up by one. Once again, NEW element!

12. Radioactive Particles • 3. Gamma Ray • Not a particle; it is high energy electromagnetic radiation • Has no mass and no charge. • Accompanies beta & alpha radiation. • Travels at the speed of light. • Highest penetrating ability - can be stopped by heavy shielding such as lead.

13. Gamma con’t • Gamma Radiation/Decay gamma particle • Gamma rays [remember the EMS (electromagnetic spectrum?)] is electromagnetic radiation similar to light. Gamma decay does not change the mass or charge of the atom from which it originates. Gamma is often emitted along with alpha or beta particle ejection. • Gamma radiation can be stopped by LEAD. • Summary of the 3:

14. Radioactive Particles Summary (thus far)

15. parent nuclide daughter nuclide alpha particle Nuclear Decay • Alpha Emission Numbers must balance!!

16. Nuclear Decay • Beta Emission • A neutron is converted in the nucleus of an atom • A new atom is formed whose atomic number is increased by 1

17. Nuclear Decay • Gamma Emission • Will not change the p+ #. It is not particulate, but rather the emission of high frequency energy to make the element more stable. • Transmutation (Alpha and Beta) One element becomes another. *note: Gamma accompanies A and B

18. Solving Problems • https://www.youtube.com/watch?v=jY0JIa-_o0E

19. More Radioactivity • Problem: sometimes atom has too many protons and not enough neutrons. Two things can happen. Option 1: • 1. Positron-  is a particle of matter with the same mass as an electron, but opposite charge (essentially, the proton emits an electron and becomes a neutron) • Watch: https://www.youtube.com/watch?v=bjuZSvZukAw

20. Questions: • What happens to atomic # when a positron is emitted?________ • How does this affect the mass #?_______

21. 11 6 11 5 0 1 0 1 e C B e +  Positron Emission: Answers: 1) At # goes down by 1; 2) Mass # is unchanged. Ex: Loss of a positron (a particle that has the same mass as but opposite charge than an electron) Note: this is a +1. Some texts may write a B (Beta) symbol instead of ‘e’

22. Summary: Types of Radiation

23. Too Many Protons? Another alternative • Electron capture - atom with too many protons may capture (‘pull IN’) an e- and the proton becomes a neutron. • Watch: https://www.youtube.com/watch?v=sg_XoUDsP08 • Questions: 1)Will the atomic # increase or decrease? __________ ; 2) How will this affect the mass #?__________

24. Answers • 1) At # will decrease by 1 (new element) • 2) Mass # will not change • Ex:

25. 0 −1 1 1 1 0 p e n +  Electron Capture (K-Capture) Addition of an electron to a proton in the nucleus • As a result, a proton is transformed into a neutron.

27. Half-life • Half-life (t½) • Time required for half the atoms of a radioactive nuclide to decay. • Shorter half-life = less stable.

28. So, what does this mean? • Let’s say you have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. • How many grams are left after one half-life? • How many grams are left after two half-lives? 50 g 25 g

29. t1/2 t1/2 t1/2 After 1 half-life Initial amount of radioisotope 100 After 2 half-lives After 3 half-lives Radioisotope remaining (%) 50 25 12.5 0 1 2 3 4 Number of half-lives Half-life of Radiation

30. 1 half-life 2 half-lives 3 half-lives 4 half-lives 16 24 32 40 48 56 Half-Life Plot 20 Half-life of iodine-131 is 8 days 15 10 Amount of odine-131 (g) 5 etc… 0 0 8 Time (days) Timberlake, Chemistry 7th Edition, page 104

31. Common Radioisotopes

32. You try it! • If the half life element A is 3 hours and you have 90 grams of it, how many grams would be left after 9 hours? • Note- I will give you problems (similar to this) that you should be able to logically figure out, without memorizing a formula. But, for those that must, it’s given on the next slide. • *Note- Don’t worry about sig figs with these!

33. Solution • Solution (by logic): Since 3 hrs is one half-life, 9 hrs is 3 half-lives. Since ½ of the sample would remain after one half-life (45 g), ½ of 45 g would remain after 2 half-lives (22.5 g) and .5 of that after the 3rd half life. Ans= 11.25 g. • *Note- Don’t worry about sig figs with these! I will tell you how many decimal places

34. To find the remaining amount… Half-life equation r :final mass i :initial mass n :# of half-lives

35. More Half-Life Equations • Total time passed (p) = n x t1/2 • To find the half-life • t1/2 = • To find the # of half lives that have passed… • n =

36. Half-life: Example (with equation) • Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t½ = 5.0 s i = 25 g r = ? p = 60.0 s n = 60.0s ÷ 5.0s =12 WORK: r = i (0.5)n r = (25 g)(0.5)12 r = 0.0061 g

37. Fission • splitting a nucleus into two or more smaller nuclei • Process used in nuclear reactors

38. Nuclear Fission • Bombardment of the radioactive nuclide with a neutron starts the process. • Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons.

39. Unstable Nucleus Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 620

40. Fission • chain reaction - self-propagating reaction

41. Nuclear Fission

42. Nuclear Reactors In nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.

43. Nuclear Reactors • The reaction is kept in check by the use of control rods. • These block the paths of some neutrons, keeping the system from reaching a dangerous supercritical mass.

44. Fusion • combining of two nuclei to form one nucleus of larger mass • thermonuclear reaction – requires temp of 40,000,000 K to sustain • occurs naturally in stars

45. Nuclear Fusion • Fusion would be a superior method of generating power. • The good news is that the products of the reaction are not radioactive. • The bad news is that in order to achieve fusion, the material must be in the plasma state at several million kelvins.

46. Synthetic Elements • Transuranium Elements • elements with atomic #s above 92 • synthetically produced in nuclear reactors and accelerators • most decay very rapidly

47. Fission vs. Fusion Alike Different Different Change Nucleus of Atoms Split large atoms U-235 Fuse small atoms 2H2 He Topic Topic Radioactive waste (long half-life) Create Large Amounts of Energy E = mc2 NO Radioactive waste Fusion Fission Nuclear Power Plants Transmutation of Elements Occurs Very High Temperatures ~5,000,000 oC (SUN)

48. Ch 19 Questions • Read Sec 19.1. Review Ex 19.1 p. 508; Read section 19.4 and 19.5. Do NOT attempt Exp 19.6. Summary problem (end of Chapter p. 525): Do A, B and C. Questions and problems: Do # 4 and 61.