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Nuclear Chemistry
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Isotopes When an atom or element can be found somewhere on Earth, it is called naturally occurring. Of the 118 elements on the periodic table, 92 are naturally occurring; the rest exist only as a result of human activity or unusual circumstances. Some elements have only one isotope, but most have more than one.
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Stable vs. Radioactive Isotopes
Stable isotopes have a stable nucleus. Stable = balance between the number of protons and neutrons in a nucleus Too few or too many neutrons will lead to the disintegration of an atom. The larger the atom, the more neutrons it takes to make a stable nucleus. Radioactive Isotopes Not stable Emit small particles (neutrons, protons, electrons, and odd mixes or variations of these particles). Called radioactive isotopes. not common; the majority of radioactive isotopes are elements with atomic numbers above 80.
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Why are some substances radioactive?
What is radiation???? Why are some substances radioactive?
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Nuclear Chemistry Radiation: particles emitted from the nucleus
Substances are radioactive because the neutron to proton ratio is “off” Radioactive substances emit radiation in order to get at n0: p+ ratio that is stable (low energy) Band of Stability
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Nuclear Radiation Radioactivity: particles or radiation emitted from a nucleus during radioactive decay Radioactive Decay: the spontaneous break-down of a nucleus into a slightly lighter nucleus, accompanied by the emission of nuclear radiation
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Types of Nuclear Radiation
1. alpha particles 2. beta particles 3. gamma rays Ionizing Radiation: can ionize atoms that they hit Emission of these types of particles (nuclear reactions) involve changes to the nucleus of the atom!
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Alpha Radiation (α) 2 protons & 2 neutrons bound together.
Nucleus of a helium atom Symbol 42He Particles do not travel far and are not very penetrating Particles can be stopped by a piece of paper! 238 92 U 234 90 Th + 4 2 He
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Beta Radiation (β) An electron that has been ejected from the nucleus
Formed when a neutron breaks down into a proton and electron Has a charge of -1 Mass 1/1837 amu Symbol: 0-1e or β Can pass through paper, but not aluminum foil or wood 14 6 14 7 -1 C N + e
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Gamma Radiation (γ) high-energy photon emitted by a radioisotope is a gamma ray (). often emitted along with alpha or beta particles during radioactive decay. have no mass and no electrical charge. extremely penetrating; can be stopped, although not completely, by several centimeters of lead.
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In your notebook..... 1. Sketch the picture below
2. Identify the type of radiation being depicted. A B C
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In your notebook..... 1. Sketch the picture below
2. Identify the type of radiation being depicted.
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Balancing Nuclear Equations
- follows law of Conservation of Mass -mass numbers for products and reactants have to equal. -atomic numbers for products and reactants have to equal. 37+0 = 37 = 19
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Balance the following nuclear equations by adding the correct particle, and complete the sentence (copy these into your notebook!) Uranium-235 undergoes _____________ decay Radium 226 undergoes _____________ decay Technecium-99 undergoes _____________ decay
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Writing nuclear equations
Write a balanced nuclear reaction for the following: 1. Potassium-37 undergoes beta decay. 2. Polonium-210 undergoes alpha decay.
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Half Life Is the time required for one-half of a sample to decay (really, to change into another element). For example, it takes 5730 years for half of a sample of carbon-14 to decay into nitrogen-14 through beta decay.
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Calculate Half Life Final Amount Time AF = AI * (.5) t/h Half-Life
Initial Amount Half-Life
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Give it a try An isotope of cesium (cesium-137) has a half-life of 30 years. If 1.0 mg of cesium-137 disintegrates over a period of 90 years, how many mg of cesium-137 would remain?
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Fission & Fusion
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Fusion Fusion: when two small nuclei combine to form a larger more stable nucleus Ex.: energy from the sun comes from nuclear fusion
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Fission Fission: a large nucleus splits apart into lighter more stable nuclei Ex.: type of reaction that occurs in a nuclear reactor
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