1. Nuclear Chemistry

2. Terms Radioactivity Radioactivity  Property of certain unstable nuclide of spontaneously emitting radiations in order to form more stable species. Nuclide --> used in place of the term nucleus  Any atom having a nucleus of mass number A, atomic number Z and number of neutrons N A Z X n Z X n

3. Isotopes Isotopes  Atoms of the same element having different atomic masses 1 H 0 2 H 1 3 H 2 1 H 0 2 H 1 3 H 2  Some isotopes are unstable that undergoes spontaneous emission of radiation Unstable nuclei  Are called radioactive isotopes or radioisotopes What are the particles that make up the nucleus?  Protons and neutrons ( nucleons)

4. Radioactive Decay Alpha,beta, and gamma decay

5. Alpha Decay a mode of decay in which the mass number changes a mode of decay in which the mass number changes Alpha is a helium particle Alpha is a helium particle 4 He. 2 4 He. 2 Formula: Formula: Parent --> alpha decay + daughter nucleus Parent --> alpha decay + daughter nucleus A P ----> 4 He + A-4 D. Z 2 Z-2 A P ----> 4 He + A-4 D. Z 2 Z-2

6. Example: 238 U ----> _______ + _______. 92 238 U ----> _______ + _______. 92 ------> 4 He + 238-4 X. 2 92-2 ------> 4 He + 238-4 X. 2 92-2 ----> 4 He + 234 X ----> 4 He + 234 X 2 90 2 90 -----> 4 He + 234 Th -----> 4 He + 234 Th 2 90 2 90

7. Exercise 1. 210 Po -----> _______, ______ 84 84 2. 219 Rn ---> _____, ______. 86

8. Beta Decay An emission of an electron from the nucleus An emission of an electron from the nucleus  A P ----> A D + 0 e z z+1 -1 Positron Decay Positron Decay  A P ----> A D + 0 e z z-1 +1  A P ----> A D + 0 e z z-1 +1

9. What happens to the nucleus when it emits beta particles? What happens to the nucleus when it emits beta particles? A P ------> A D 0 e.. Z+1 -1 A P ------> A D 0 e.. Z+1 -1 Ex: 40 K ----> 40 Ca + 0 e 19 20 -1 19 20 -1

10. Positron Decay  A P ----> A D + 0 e z z-1 +1  A P ----> A D + 0 e z z-1 +1 Nitrogen 12 after emitting a positron becomes carbon 12 Nitrogen 12 after emitting a positron becomes carbon 12 12 N -------> 12C + 0 e. 7 6 +1 12 N -------> 12C + 0 e. 7 6 +1 Complete the ff nuclear reactions: 1. _____ ---> 30 Si + 0 e. 14 +1 2. 14 O ------> 14 N + ____

11. Practice Complete the ff nuclear reactions: 1. _____ ---> 30 Si + 0 e. 14 +1 2. 14 O ------> 14 N + ____

12. Exercises Complete the following nuclear reactions Complete the following nuclear reactions a) 14 C ---> _______ + 0 e. 6 -1 b) 30 Al ---> _____________ + 0 e 13 -1

13. Electron-capture Is a process in which one of the inner orbital electrons is captured by the nucleus Is a process in which one of the inner orbital electrons is captured by the nucleus Results in a decrease in Z-number of the daughter nucleus and no change in A-number Results in a decrease in Z-number of the daughter nucleus and no change in A-number Ex: 201 Hg + 0 e ---> 201 Au + gamma rays 80 -1 79 80 -1 79

14. Write the nuclear reaction involved when Ba-133 captures an orbital electron 133 Ba + 0 e = _____ + _____ 56 -1 56 -1 133 Cs + X-rays 133 Cs + X-rays 55 55

15. Gamma Decay Gamma Rays are high energy radiation similar to X-Rays Gamma Rays are high energy radiation similar to X-Rays mass number and atomic number of the nucleus remains the same mass number and atomic number of the nucleus remains the same Only energy changes Only energy changes 60 Co --------> 60 Co + gamma rays 60 Co --------> 60 Co + gamma rays 27 27 27 27

16. What is the difference between gamma rays, x-rays and visible light? Gamma rays is identical to x-rays except that it originates from the nuclei Gamma rays is identical to x-rays except that it originates from the nuclei X-rays and visible light rays originate in the electron shell of the atom X-rays and visible light rays originate in the electron shell of the atom

17. Ray Charge Nature Penetrating Power Alpha Helium ion Has very low penetrating- can be stopped by a paper Betaelectron Slight penetrating –can be stopped by a thin sheet of Al Gamma No charge behaves like an x-ray Very penetrating Needs a thick sheet of lead to stop

18. Half Life Time required for half of the nuclei in a sample to undergo radioactive decay Time required for half of the nuclei in a sample to undergo radioactive decay Ex: Thorium-234 has a half life of 24 days. Suppose you have 1 gram sample,what fraction exist after 3 half lives? Four half lives? Five half lives? Time # of t= ½ amt. Remaining 0 1 0 1 24 1 1/2 48 2 1/4 72 3 1/8 96 4 1/16

19. Exercise strontium-90 has a half life of 28 years. If we have 60g of strontium 90 today, how many grams will be left after 56 years? 84 years later? strontium-90 has a half life of 28 years. If we have 60g of strontium 90 today, how many grams will be left after 56 years? 84 years later? H-3 has a half life of 12.46 years. How long must a sample be stored so that only ¼ of the original is left? H-3 has a half life of 12.46 years. How long must a sample be stored so that only ¼ of the original is left? The half life of radon 222 is 4 days. If you start with 5.o g how much will be left in 16 days? The half life of radon 222 is 4 days. If you start with 5.o g how much will be left in 16 days?

20. Why are some nuclie stable and others are unstable?

21. Nuclear Stability Stability of isotopes is based on the ratio of neutrons and protons in a nucleus. Stability of isotopes is based on the ratio of neutrons and protons in a nucleus. Stable  n/p = 1 Stable  n/p = 1 Generally, ratio between 1-1.6 is stable

22. Ex: stable nuclei Carbon 12 -  p = ? n =? Carbon 12 -  p = ? n =? p = 6 n = 6 p = 6 n = 6 n/p = 1 n/p = 1 Pb-206 -  p = ? n =? Pb-206 -  p = ? n =? p = 82 n =124 p = 82 n =124 n/p = 124/82 = 1.5 n/p = 124/82 = 1.5

23. Example of unstable nuclei H-3 -------> p= ? n=? H-3 -------> p= ? n=? p= 1 n = 2 p= 1 n = 2 n/p = 2 n/p = 2 2 is more than 1.6 so it is unstable S -31 ------> p = ? n =? p = 16 n = 15 p = 16 n = 15 n/p = 15/16 = 0.94 n/p = 15/16 = 0.94

24. Note: elements with atomic # >83 have no stable isotopes because 83 is the highest # of protons that can be accommodated in a stable nucleus

25. Odd-Even number of the nucleus also plays an important role in the stability of the nuclei even # of protons and neutrons are most stable even # of protons and neutrons are most stable Odd # of protons and neutrons are least stable Odd # of protons and neutrons are least stable Even-odd # of protons and neutrons are intermediate Even-odd # of protons and neutrons are intermediate

26. Exercise Based on the ideas presented, can you predict which nuclei is stable? unstable/radioactive? Explain your answer Based on the ideas presented, can you predict which nuclei is stable? unstable/radioactive? Explain your answer a) Pb- 208 b) Ca-40 c) As-76

27. Radiocarbon Dating Every living things contain carbon. Every living things contain carbon. There are two kinds of Carbon, carbon-12 and carbon-14 There are two kinds of Carbon, carbon-12 and carbon-14 Carbon14 is radioactive Carbon14 is radioactive Living organisms have the same amount of carbon-14. But when it dies it stop taking in carbon-14 Living organisms have the same amount of carbon-14. But when it dies it stop taking in carbon-14 Age of certain fossil is determined by how much carbon-14 is left Age of certain fossil is determined by how much carbon-14 is left

28. Radiocarbon Dating Radiocarbon Dating Method used to determine the ages of materials which were once living Method used to determine the ages of materials which were once living It is based on the radioactivity of carbon-14 which decays by beta particle production It is based on the radioactivity of carbon-14 which decays by beta particle production 14 C ----> 0 e + 14 N. 6 -1 7 14 C ----> 0 e + 14 N. 6 -1 7 14 N + 1 n -----> 14 C + 1 H 7 0 6 1 14 N + 1 n -----> 14 C + 1 H 7 0 6 1 Carbon half-life is 5730 years Carbon half-life is 5730 years

29. Applications of Radioactivity

30. What makes radioisotopes useful in diagnostic procedure? Ex: Iodine131 is used as therapy for hyperthyroidism Ex: Iodine131 is used as therapy for hyperthyroidism  The radiation destroys the fast growing cells in the thyroid gland

31. Common radioisotopes in Medical Technology Arsenic-74 Arsenic-74  locates brain tumor  locates brain tumor Iodine 131 Iodine 131  detects thyroid malfunction  detects thyroid malfunction Radium 226 Radium 226  Used for radiation therapy for cancer  Used for radiation therapy for cancer Cobalt-60 Cobalt-60  detect and treat tumors  detect and treat tumors

32. Medical Application Radiotracers Radiotracers  Radioactive nuclide that can be introduced into organisms in food or drugs and subsequently traced by monitoring their radioactivity

33. Other Uses of Radioisotopes Producing weapons of war Producing weapons of war Irradiation of food for preservation Irradiation of food for preservation Nuclear Power for electricity Nuclear Power for electricity

34. Nuclear Power for electricity Generating electricity from the nucleus of the atom. Generating electricity from the nucleus of the atom. Nuclear disasters caused doubts on the advantages of nuclear energy. Nuclear disasters caused doubts on the advantages of nuclear energy.

35. Producing Weapons Atomic Bombs Atomic Bombs  Was dropped in Japan  Causing death and destruction Hydrogen Bombs Hydrogen Bombs

36. Irradiation of food for preservation Studies shows that when food products were processed through controlled doses of x-rays or gamma rays the ff: were observed: Studies shows that when food products were processed through controlled doses of x-rays or gamma rays the ff: were observed:  Low dosage: kills any insects that remain after harvest  Medium dosage: reduces the population of salmonella bacteria in fish, poultry and other meats  High dosage: sterilizes poultry and other meats