chapter 7 nuclear changes chapter 7 section 1: radioactivity what is radioactivity? ◦...
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- CHAPTER 7 NUCLEAR CHANGES
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- Chapter 7 Section 1: Radioactivity What is radioactivity? Radioactivity is the process by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation
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- Nuclear Radiation Radioactive materials have unstable nuclei Nuclei change by releasing energy. Elements can transform into isotopes of the same element or into entirely different elements
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- Nuclear Decay As elements change or transform they undergo nuclear decay. Carbon dating uses rates of nuclear decay The released energy is called Nuclear Radiation Can cause damage to living tissue
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- When a radioactive atom decays, the nuclear radiation leaves the nucleus. The radiation is now able to react with any surrounding matter The reaction depends on the charge, mass, & energy of the nuclear radiation
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- Types of Nuclear Radiation 4 types of nuclear radiation: Alpha Particles Beta Particles Gamma Rays Neutron Emission
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- Alpha Particles Positively charged & more massive than any other type of nuclear radiation Discovered by Ernest Rutherford (also discovered the nucleus) Consist of 2 protons & 2 neutrons
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- Alpha Particles Do not travel far through materials (can barely pass through paper) The massive size of alpha particles limits their movement Remove electrons from surrounding matter as they pass through it (_______________) Ionization causes alpha particles to slow down
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- Beta Particles Fast-moving Electrons produced by neutron decay Negatively charged particles Travels farther through matter compared to alpha particles
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- How can electrons come from a positively charged nucleus? In the 1930s, it was discovered that as a neutron (neutral charge) decays it forms a proton & electron The electron has very little mass and gets ejected from the nucleus at a high speed as a Beta Particle
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- Gamma Rays Very High Energy Light 1898- Marie Curie isolated radioactive radium 1900- Paul Villiard discovered that radium emitted a new type of nuclear radiation
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- Gamma Rays! More penetrating than Beta particles Gamma rays are not made of matter & do not have an electric charge Gamma rays are a form of electromagnetic energy
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- Have more energy than X-rays Do not ionize surrounding matter Can penetrate 60cm of aluminum & 7 cm of lead! Not easily stopped by clothing or building materials Can be very harmful
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- Neutron Emission Neutron Emission is the release of a high-energy neutron by some neutron-rich nuclei during radioactive decay. Emitted from an unstable nucleus Do not ionize surrounding matter Travel farther through matter than or
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- Nuclear Decay When an unstable nucleus emits alpha or beta particles, the # of protons or neutrons changes. Example: Radium-226 changes to Radon-222 by emitting an alpha particle
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- A nucleus gives up 2 protons & 2 neutrons during alpha decay Nuclear decay processes can be written similar to a chemical reaction equation The nucleus before the decay is like the reactant The nucleus after the decay is like the product
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- A nucleus gains a proton & loses a neutron during beta decay Equation is formed the same way except the symbol for a beta particle is used. In all cases of beta decay, the mass number before & after the decay doesnt change
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- When writing the equation Write the original element on the left side (reactants) X is used for the unknown symbol A is used for the unknown mass Z is used for the unknown atomic # Solve for the unknowns & rewrite the balanced equation
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- Radioactive decay rates A substances half-life is the time in which half of the radioactive substance decays (A measure of how quickly a substance decays) After each half-life passes half of the sample remains unchanged.
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- Practice Problem Radium has a half-life of 1599 years. How long would it take seven-eights of radium-226 sample to decay? 1- 7/8 = ______ x x =______ How many half-lives?______
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- Each half-life is 1599 years It takes 3 half-lives to have 1/8 radium remaining. 3 x 1599 = 4797 years
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- More Practice! (pg. 228) Carbon- 14 has a half life of 72 hours. How long would it take for 15/16 of the carbon sample to decay?
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- Uranium-238 decays very slowly, with a half-life of 4.47billion years. What percentage of the sample would remain after 13.4 billion years?
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- A sample of strontium-90 is found to have decayed to 1/ 8 of its original amount after 87.3 years. What is the half-life of strontium?
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- A sample of francium-212 will decay to 1/16 its original amount after 80 minutes. What is the half- life of francium-212?
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- What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 grams in 21.6 seconds?
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- The half-life of hafnium-156 is 0.025 seconds. How long will it take a 560 g sample to decay to one-fourth of its original mass?
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- Potassium-42 has a half-life of 12.4 hours. How much of an 848 g sample of potassium-42 will be left after 62.0 hours?
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- Half-life practice Gold-210 is a radioactive isotope that has a half-life of 12 hours. If a lab starts with a 13milligram sample of gold- 210, how much will remain after 37 hours?
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- Chapter 7 Section 2 Nuclear Fission & Fusion
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- Nuclear Force Elements can have both stable & unstable isotopes. Example: Carbon-12 is stable Carbon-14 is unstable & The stability of a nucleus depends on the nuclear forces that hold the nucleus together
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- Nuclei are held together by a particular force Strong Nuclear Force is the interaction that binds protons & neutrons together in a nucleus Force is much stronger than the repulsion force between protons Strong nuclear forces occur at very short distances (3 x 10 -15 m)
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- In stable nuclei the attractive forces are stronger than repulsion forces Too many neutrons or protons can cause a nucleus to become unstable & decay
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- Nuclei with too many neutrons or too few are unstable & will undergo decay Nuclei with more than 83 protons are always unstable Atomic numbers will be greater than _____
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- Nuclear Fission The process of producing lighter nuclei from heavier nuclei is called Fission First observed by Otto Hahn & Fritz Strassman in 1939 Their experiment bombarded Uranium-235 with neutrons
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- The Product 2 lighter nuclei, neutrons, & energy Barium-137 & Kryton-84 The product includes 15 neutrons Uranium can undergo many types of fission with different products
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- Energy is released during Nuclear Fission During Fission the nucleus breaks into smaller nuclei The reaction releases large amounts of energy Each dividing nucleus releases about 3.2 x10 -11 J of energy
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- Hahn & Strassman determined the overall masses of the elements in their reaction had decreased after the reaction. The missing mass had changed to Energy!
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- The Theory of Relativity Presented by ___________ __________ in 1905 Describes the equivalence of mass & energy observed in nature Equivalence means that matter can be converted into energy & energy into matter.
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- E = mc 2 Energy = mass x (speed of light) 2
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- Neutrons released by fission can start a chain reaction! When a nucleus splits into lighter nuclei, they need less neutrons so the neutrons are emitted. The emitted neutron can then collide with surrounding nuclei and undergo fission
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- Nuclear Chain Reaction A series of fission processes in which the neutrons emitted by the dividing nucleus cause the division of the other nuclei
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- Chain reaction is the principle behind the nuclear bomb!
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- Chain reactions can be controlled The more neutrons that are produced per reaction the great the chances of creating a chain reaction Specific materials can be used that will slow a fission chain reaction by absorbing neutrons
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- Nuclear Fusion (Hydrogen Bomb) Energy can be obtained when light nuclei are combined into heavy nuclei Fusion is the process in which light nuclei combine at extremely high temperatures forming heavier nuclei & releasing energy
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- Chapter 7 Section 3 Dangers & Benefits of Nuclear Radiation
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