1 Nuclear Chemistry

2 The stability of the atom The vast majority of all atoms are incredibly stable and their nucleus never changes. However, a small percentage of atoms will have their nucleus break apart and give off radiation. This breaking apart is called decay. Decay can happen naturally or we can force it to happen through nuclear reactions.

3 Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

4 Radioactive Decay Most of the isotopes which occur naturally are stable. Some unstable isotopes are said to be radioactive. –Radioactive (unstable) isotopes are called radioisotopes Radioisotopes eventually decay and change into more stable forms. The stable form is a different element. This process is called transmutation.

5 Often times, when a radioisotope decays and becomes stable it will release a particle and change into a different element. Some radioisotopes release energy by emitting radiation during the process of decay.

6 Examples of radioactive isotopes

7 Radioactive decay results in the emission of either: an alpha particle (  ); a positively charged helium isotope; contains two neutrons and two protons a beta particle (  ); a high speed electron ;or a gamma ray  Electromagnetic radiation; pure energy; called a ray rather than a particle Radioactive Decay

8 Examples of radioactive decay C-14  N-14 + beta particle P-32  S-32 + beta particle I-131  Xe beta particle U-238  Th alpha particle

9 Penetrating Ability

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11 Half-Life Chemists are interested in the amount of time it takes for elements to decay into another element. They use the term “half-life” to measure the time it takes an element to decay.Chemists are interested in the amount of time it takes for elements to decay into another element. They use the term “half-life” to measure the time it takes an element to decay. HALF-LIFE is the time that it takes for 1/2 a sample to decompose.HALF-LIFE is the time that it takes for 1/2 a sample to decompose.

12 Examples of half life Lead-210 has a half life of 22 years. If you start with 80 g of Pb-210…. After 22 years, you’ll have 40 g of Pb-210 After 44 years, you’ll have 20 g of Pb-210 After 66 years, you’ll have 10 g of Pb-210 After 88 years, you’ll have ______ of Pb-210

13 Po-218 has a half-life of 3 minutes If you start with a sample of 100 g of Po-218 How much is left after 1 half life? ___ How much is left after 2 half lives?____ How much is left after 4 half lives? ____

14 Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives? What is the half-life?

15 1)What is the half-life? 2)How long is 3 half-lives? How much is left?

16 If we start with 200 atoms of a radioactive substance, how many would remain after one halflife?_________ after two half-lives? _________ after three half-lives? ___________ after four halflives?__________

17 1)What is the half life? 2)How long for 3 half lives?

18 Forcing the atom to split up Fission- A reaction in which an atomic nucleus of a radioactive element splits by bombardment from an external source, with simultaneous release of large amounts of energy, used for electric power generation.

19 Nuclear Fission Fission is the splitting of atoms These are usually very large atoms, that they are not very stable.

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21 Nuclear Fission & POWER Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. 17% of the world’s energy comes from nuclear.17% of the world’s energy comes from nuclear.

22 Figure 19.6: Diagram of a nuclear power plant.

23 Nuclear Fusion The opposite of Fission Fusion small nuclei combine 2 H + 3 H 4 He + 1 n Occurs in the sun and other stars; has ne Energy

24 Fusion Excessive heat can not be contained Attempts at “cold” fusion have FAILED. “Hot” fusion is difficult to contain

25 Draw a Double Bubble Map of Fusion and Fission fusion fission Differences Similarities Differences

26 local.k12.oh.us/Downloads/9- 29_Half%20Life%20Worksheet.pdf

27 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 days If 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

28 Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

29 Effects of Radiation

30 Geiger Counter Used to detect radioactive substances

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32 Radiocarbon Dating Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation 14 N + 1 o n ---> 14 C + 1 H The C-14 is oxidized to CO 2, which circulates through the biosphere. When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t 1/2 = 5730 years. Activity of a sample can be used to date the sample.

33 Nuclear Medicine: Imaging Thyroid imaging using Tc-99m

34 Food Irradiation Food can be irradiated with  rays from 60 Co or 137 Cs.Food can be irradiated with  rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration.Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs.USDA has approved irradiation of meats and eggs.