1 Chapter 22 - Nuclear Chemistry

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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 radioactive decay, the spontaneous disintegration of some elements into smaller pieces.She discovered radioactive decay, the spontaneous disintegration of some elements into smaller pieces.

4 Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleusNuclear reactions involve the nucleus The protons and neutrons are rearrangedThe protons and neutrons are rearranged This releases a tremendous amount of energyThis releases a tremendous amount of energy This energy was used to hold the nucleus together and is called binding energyThis energy was used to hold the nucleus together and is called binding energy “Normal” Chemical Reactions involve electrons, not protons and neutrons“Normal” Chemical Reactions involve electrons, not protons and neutrons

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6 Types of Radiation Alpha Particle (α) – two protons and two neutrons – a helium nuclei with a charge of 2 + Alpha Particle (α) – two protons and two neutrons – a helium nuclei with a charge of 2 + Beta Particle (β) – an electronBeta Particle (β) – an electron Gamma ray (γ) –high energy electromagnetic wavesGamma ray (γ) –high energy electromagnetic waves

7 Other Nuclear Particles Neutron Neutron Positron – a positive electron Positron – a positive electron Electron capture – electron captured by the nucleus so found on the reactant side of the equationElectron capture – electron captured by the nucleus so found on the reactant side of the equation Proton – usually referred to as hydrogen-1Proton – usually referred to as hydrogen e

8 Balancing Nuclear Reactions In the reactants and products Atomic numbers must balance and Mass numbers must balance Use a particle or isotope to fill in the missing protons and neutrons

9 Balancing Nuclear Reactions Alpha emissionAlpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved

10 Balancing Nuclear Reactions Beta emissionBeta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.

11 Balancing Nuclear Reactions Positron ( 0 +1  ): a positive electron Electron capture: Electron capture: the capture of an electron 207

12 Learning Check What radioactive isotope is produced in the following alpha bombardment of boron-10? 10 5 B He → ? n

13 Learning Check Nitrogen – 13 plus a neutron is produced by the bombardment of boron? 10 5 B He → 13 7 N n

14 Write Nuclear Equations! Write the nuclear equation for the beta emitter Co Co  Ni β

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16 Half-Life The amount of time that it takes for ½ the mass of a radioactive nuclide to decay. Each nuclide has a half-life that is unique to that nuclide

17 Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?

18 Problem The half life of Polonium-218 is 3.0 minutes. If you begin with 10.0 grams, how much would remain after 9.0 minutes? Time Mass 0.0 minutes 10.0 grams 3.0 minutes 5.0 grams 6.0 minutes 2.5 grams 9.0 minutes 1.25 grams

19 Your Turn The original mass of P-32 is 4.0 mg. The half-life of P-32 is 14.3 days. How much P-32 will remain after 57.2 days? Time Mass 0.0 days 4.0 mg 14.3 days 2.0 mg 28.6 days 1.0 mg 42.9 days.5 mg 57.2 days.25 mg

20 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.

21 Radiation Exposure Exposure to radiation can cause cancer and genetic effects by damaging the DNA. Everyone is exposed to environmental background radiation – about.030 to.150 rems is normal.500 rems is acceptable according to the U.S. Government.

22 Effects of Radiation

23 Penetrating Ability

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25 Nuclear Fission

26 Nuclear Fission Fission is the splitting of unstable, very heavy nuclei into more stable nuclei of intermediate mass.Fission is the splitting of unstable, very heavy nuclei into more stable nuclei of intermediate mass. The process produces an enormous amount of energyThe process produces an enormous amount of energy

27 Representation of a fission process

28 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. About 20% of the U. S. energy comes from nuclear.About 20% of the U. S. energy comes from nuclear.

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30 Diagram of a nuclear power plant

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35 Nuclear Fusion Fusion small nuclei combine 2 H + 3 H 4 He + 1 n Occurs in the sun and other stars Energy

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37 Nuclear Medicine: Imaging Thyroid imaging using Tc-99

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39 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.