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Nuclear Chemistry

Nuclear Chemistry. Terms. 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

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Nuclear Chemistry

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  1. Nuclear Chemistry

  2. Terms • 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 ZXn

  3. Isotopes • Atoms of the same element having different atomic masses 1H02 H13H2 • 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 • Alpha is a helium particle • 4 He .2 Formula: Parent --> alpha decay + daughter nucleus A P ----> 4 He + A-4 D . Z 2 Z-2

  6. Example: • 238U ----> _______ + _______ .92 ------> 4He + 238-4 X . 292-2 ----> 4 He + 234 X 290 -----> 4He + 234 Th 2 90

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

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

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

  10. Positron Decay Positron Decay AP ----> A D + 0e z z-1 +1 • Nitrogen 12 after emitting a positron becomes carbon 12 12N -------> 12C + 0 e .76 +1 Complete the ff nuclear reactions: • _____ ---> 30Si + 0e . 14 +1 • 14 O ------>14 N + ____

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

  12. Exercises • Complete the following nuclear reactions • 14 C ---> _______ + 0 e . 6-1 • 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 • Results in a decrease in Z-number of the daughter nucleus and no change in A-number Ex: 201Hg + 0e ---> 201Au + gamma rays 80-179

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

  15. Gamma Decay • Gamma Rays are high energy radiation similar to X-Rays • mass number and atomic number of the nucleus remains the same • Only energy changes 60Co -------->60 Co + gamma rays 2727

  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 • X-rays and visible light rays originate in the electron shell of the atom

  17. Half Life • 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 24 1 1/2 48 2 1/4 72 3 1/8 96 4 1/16

  18. 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? • 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?

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

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

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

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

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

  24. 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 • Odd # of protons and neutrons are least stable • Even-odd # of protons and neutrons are intermediate

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

  26. Radiocarbon Dating • Every living things contain carbon. • There are two kinds of Carbon, carbon-12 and carbon-14 • Carbon14 is radioactive • 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

  27. Radiocarbon Dating • 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 14C ----> 0e + 14N . 6-17 14N + 1n -----> 14C + 1H 706 1 • Carbon half-life is 5730 years

  28. Applications of Radioactivity

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

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

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

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

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

  34. Producing Weapons • Atomic Bombs • Was dropped in Japan • Causing death and destruction • Hydrogen Bombs

  35. 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:  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

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