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Nuclear Chemistry Nuclear chemistry is the study of the changes of the nucleus of atoms. Nuclear Reactions involve changes within the nucleus where as chemical reactions involve the loss, gain or sharing of electrons.

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The Nucleus Remember that the nucleus is made up of protons and neutrons. The are collectively called nucleons.

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Radioactivity A stable nucleus holds together well. An unstable nucleus will decay or break down, releasing particles and/or energy in order to become stable. An atom with an unstable nuclei is considered “radioactive”.

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**Nuclear Transformations**

Nuclear transformations can be induced by accelerating a particle and colliding it with the nuclide. These particle accelerators are enormous, having circular tracks with radii that are miles long.

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**There are several ways radioactive atoms can decay into different atoms!**

Transmutation: Type of nuclear reaction that will change the number of protons and thus will create a different element. Atoms with an atomic number larger than 92 are created through this process

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**He α U Th He Alpha Decay Loss of an -particle (a helium nucleus)**

Atomic number decreases by 2 and mass number decreases by 4 Penetrating Power: LOW: Can be blocked by clothing or thin paper Example OR He 4 2 α 4 2 U 238 92 Th 234 90 He 4 2 +

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Alpha Decay

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Alpha Decay Uranium Thorium

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** e I Xe e Beta Decay Loss of a -particle (a high energy electron)**

Atomic number increases by 1 and mass number stays the same. A neutron becomes a proton and a high speed electron that is discharged from the nucleus. Penetrating Power: Medium: Can be blocked by thin metal or wood Example −1 e or I 131 53 Xe 54 e −1 +

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Beta Decay

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Beta Decay Thorium Protactinium

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Gamma Emission Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle) Atomic number and mass number stays the same Penetrating Power: High: Can only be blocked by thick metal or thick concrete Example I 131 53 e +

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Radioactivity Radioactive isotopes decay at a characteristic rate measured in half life. A half life is the time required for half of the amount of radioactive atoms to decay. The time ranges from seconds to millions of years

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**Np Pu ____ Examples Beta decay of zircomium-97 **

Alpha decay of americium-241 Alpha decay of uranium-238 Complete this: Np 235 93 Pu 239 94 ____ +

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**Common Radioactive Isotopes**

Isotope Half-Life Radiation Emitted Carbon ,730 years b, g Radon days a Uranium x 108 years a, g Uranium x 109 years a

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**Radioactive Half-Life**

After one half life there is 1/2 of original sample left. After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.

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**Graph of Amount of Remaining Nuclei vs Time**

A=Aoe-lt A

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**Half Life Calculations**

HOW TO’s 1. To calculate the number of half lives, divide the half life (T1/2) into the total time (T). T/T1/2 = # of half lives 2. Use the equation to calculate remaining amount left over after a certain number of half lives have passed. Amt remaining = (initial amt) (.5)n (# of half lives)

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Example 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?

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Examples Suppose you have 20 grams of sodium-24. Its half-life is 15 hours. How much is left over after 60 hours.

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Examples Uranium-238 has a half life of 4.46 x 109 years. How long will it take for 7/8th of the sample to decay?

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Examples The half life of radium-222 is 38 s. How many grams of a 12.0 g sample are left after 114 s?

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**Examples A sample of 3x107 Radon atoms are trapped**

in a basement that is sealed. The half-life of Radon is 3.83 days. How many radon atoms are left after 31 days? answer:1.2x105 atoms

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**Nuclear Fission: How does one tap all that energy?**

Large atoms split into smaller atoms that generate huge amounts of energy. Carried out in nuclear reactors. Could result in a chain reaction of fission like the atomic bomb

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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. This process continues in what we call a nuclear chain reaction.

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Nuclear Fission If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out. Therefore, there must be a certain minimum amount of fissionable material present for the chain reaction to be sustained: Critical Mass.

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

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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.

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**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. Tokamak apparati like the one shown at the right show promise for carrying out these reactions. They use magnetic fields to heat the material.

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**Nuclear Fusion Smaller atoms are combine to form a large atom.**

Occurs in the sun and stars Generates huge amounts of energy

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Chapter 21 Nuclear Chemistry

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