chapter 9 notes. while chemical changes involve changes in the electrons (ex : bonding), nuclear...
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Post on 18-Dec-2015
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- Slide 1
- Chapter 9 Notes
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- While chemical changes involve changes in the electrons (ex : bonding), nuclear reactions involve changes to the nucleus and involve much larger energies than chemical reactions. Atoms are made of particles Protons (+) Neutrons (no charge) Electrons (-)
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- Particles in the nucleus are attracted together by the strong force Causes protons and neutrons to stick together While the nuclear force is extremely weak at most distances, over the very short distances present in the nucleus the force is greater than the repulsive electrical forces among protons. Protons all have positive charges which should repel If it is not strong enough to keep large nuclei together = this is what causes radiation!!
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- When the attractive nuclear forces and repulsive electrical forces in the nucleus are not balanced, the nucleus is unstable Large nuclei are unstable and often decay! (aka, radiation) If protons are too far apart to be attracted by the strong force, they are repelled by the electric force between them.
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- What charge do protons have?? ________ What two particles are in the nucleus? ___________ and ____________ What is the force that holds the nucleus together? _______________________ Can the strong force hold together a large nuclei? ____________ Positive ProtonsNeutrons Strong Force No!
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- Through radioactive decay, the unstable nucleus releases radiation in the form of very fast-moving particles and energy to produce a new nucleus, and changes the identity of the element These elements are known as radioactive Uses of radioactive isotopes: Medical applications The radiation they release can be used to kill undesired cells (ex: cancer cells) Radioisotopes can be introduced into the body to show the flow of materials in biological processes.
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- You cant hear, touch, see, taste, or smell radioactivity (small amounts are all around you though!!!) Henri Becquerel discovered radioactivity accidentally in 1896 when he left a uranium salt in his desk drawer with a photographic plate. When he removed the plate and developed it, he found the outline of the clumps of the uranium salt. He hypothesized that the uranium had given off some sort of invisible energy He called it radiation
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- Half-Life - a measure of the amount of time it takes for half the nuclei in a sample of an isotope to decay Remember an isotope is an element with same number protons and different numbers of neutrons in the nucleus For any radioisotope, the half-life is unique and constant. Graphs can be made that show the amount of a radioisotope that remains as a function of time and can be interpreted to determine the value of the half-life Each element has a different half-life
- Slide 9
- Carbon-14 is used to find the age of once-living things. When animals eat plants, they take in carbon-14. Carbon-14 decays into nitrogen-14 The half-life of carbon-14 is 5,730 years The amount of carbon-14 stays constant in a living organism. Once the organism dies, the amount of carbon-14 decreases at a regular rate.
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- Carbon-14 has a half-life of 5,730 years. How much of a 100 g sample of carbon- 14 will remain after: 5,730 years? _____________ 11,460 years? ____________ 17,190 years? ____________ 22,920 years? ____________ 50 g 25 g 12.5 g 6.25 g
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- Nuclear Fission process of splitting a nucleus into two nuclei with smaller masses, releasing large amounts of energy Fission = divide Only atomic #s above 90 can undergo nuclear fission Released energy can be used for electricity or nuclear weapons
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- A chain reaction is an ongoing series of fission reactions This is how nuclear power plants generate electricity
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- Nuclear Fusion 2 nuclei with low masses are combined to form one nucleus of larger mass Fusion = together To occur, positively charged nuclei must move very fast to overcome alike charge repulsion More kinetic energy = more temperature Must occur at very high temperatures
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- Found in the center of stars and the sun As the sun ages, there is less hydrogen and more helium because of hydrogen combining
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- Which type of nuclear energy combines elements together at very high temperatures? _______________________ Which type of reaction is shown below? Nuclear Fusion Nuclear Fission
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