Nuclear Chemistry Questions And Answers

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Willhelm Roentgen
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(1845-1923) discovered X-rays, a high energy form of light (1895)
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Henri Becquerel
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(1852-1909) found that uranium ores emit radiation that can pass through objects (like x-rays) and affect photographic plates (1896)
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Marie Sklodowska Curie
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(1867-1934) Marie and Pierre worked with Becquerel to understand radioactivity. Shared a Nobel prize in physics in 1903. She later won a nobel prize in chemistry in 1911/
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E.O. Lawrence
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Invented the cyclotron which was used at UC Berkeley to make many of the transuranium elements
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Radioactivity
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The spontaneous breakdown of atomic nuclei, accompanied by the release of some form of radiation (also called radioactive decay)
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Half-life
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Time required for half of a radioactive sole to decay
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Transmutation
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One element being converted into another by a nuclear change
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Nuclides
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Isotopes of elements that are identified by the number of their protons and neutrons
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Decay series
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The sequence of Nuclides that an element changed into until It forms a stable nucleus
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Radioactive dating
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Using half life information to determine the age of objects. C-14/C-12 is common for organic artifacts. Uranium is common for rocks
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Nuclear fission
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Large nucleus breaking down into pieces of about the same mass
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Nuclear fusion
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Two or more light nuclei blend to form one or more larger nuclei
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Types of radiation
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Alpha particles, beta particles, gamma rays
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Alpha particles
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Same as a helium nucleus, 4/2 He, w a mass of 4 amu. Travels about 1/10th speed of light, most easily stopped of the particles, least dangerous
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Beta particles
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High speed electrons, 0/-1e, with a mass of 0.00055 amu and travel at nearly the speed of light, they can be stopped by a sheet of aluminum, more penetrating/dangerous than alpha
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Gamma rays
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Extremely high energy light, y, with no mass, and are the most penetrating (several cm’s of lead are needed to stop them) they can cause severe damage
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Positron emission
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Emission of positron from nucleus 0/+1e
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Electron capture
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Inner electrons captured by nucleus 0/+1e, caused when electron becomes proton, outer electron fills vacancy…giving off energy
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Variables in half life problems
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Total time, starting amount, half life, ending amount
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Half life graph characteristics
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Time it takes for the amount of substance or the activity of the substance to drop to half is the same WHEREVER you start on the graph. This is a first-order reaction. Half lives can range
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Symbols for important particles
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Alpha 4/2He, Beta 0/-1e, positron 0/+1e, neutron 1/0n
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Decay in equations
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The particle is on the right side of the equation
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Reasons for a nucleus to be unstable
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The nucleus has too many protons compared to neutrons (positron decay) The nucleus has too many neutrons compared to protons (beta decay) The nucleus is too big (alpha decay)
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Stable nucleus
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N:p Ratio between 1 and 1.5
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Radioactive dating
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You can calculate the time needed to change from what is expected to what is actually found
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Radioisotopes
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Many substances can be radioactive and then followed as they move through the body
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Fission reactors
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Current nuclear reactors use fission reactions to produce heat which is used to turn water into steam and drive turbine engines that produce electricity
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The sun and stars
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Powered by nuclear fusion…this is related to the fact that the most abundant element in the universe is hydrogen…followed by helium
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Fissionable
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Means element can be split when bombarded by neutrons
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Chain reaction
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Each spitting nucleus can emit neutrons that can split other nuclei is the basis
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Breeder reactors
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Use different isotoprs
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Fusion in the Sun
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Involves several steps – 4(1/1H)–> 4/2He+2 0/1e+energy
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Thermonuclear devices
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Use isotopes of hydrogen (deuterium and tritium)
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E=mc^2
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equation Basis for explaining where energy associated with nuclear changes comes from
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Mass defect
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When a nuclear change occurred, the mass of the products is slightly less than the mass of the reactants. The loss in mass is called the mass defect
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Variables in mass defect equations
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e= the energy m=the mass defect c= the speed of light, 3.000 c 10^8 m/s
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1 kg of mass converted into energy
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Equivalent to burning 3 billion kg of coal
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During beta decay
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1 neutron changes into 1 proton + 1 negative beta particle (the atomic # increases by one due to the new proton. The mass # is unchanged… A neutron is gone. To maintain electrical neutrality, a negative beta particle is also formed
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During positron decay
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1 proton changes into 1 neutron+1 positron particle (the atomic # decreases by one due to the loss of a proton. Since it changed into a neutron the mass # is unchanged)
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Daughter isotope
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Often unstable after decay, many decays may occur before stable nucleus is formed
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Characteristic decay series
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Method used to verify the identity of newly formed atoms
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Nuclear waste problem
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Daughter products can be even more radioactive than parent so disposal/storage is a problem
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Useful characteristic of decay particle
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Ionize the air as they pass through by striking atoms and knocking off electrons
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Geiger counters
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Detects and measures radiation by: radioactive particles pass through chamber with two electrodes, ionized particles migrate to + and – electrodes and complete the circuit
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Smoke detectors
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Use tiny piece of radioactive Am to keep circuit flowing due to ionized particles. Smoke particles attract ionized particles, break the circuit, and set off alarm
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Brushes
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Kept ionized by tiny bits of radioactive material to more easily attract tiny bits of dust
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Glenn Seaborg and Al Ghiorso
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At UC Berjeley were able to use E.O. Lawrence’s cyclotron to make larger atoms (elements 93 and 94)
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Largest naturally occurring element
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Uranium Z=92
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New element uses
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Medical field, further understanding of nucleus
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Largest element
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As of July 2000, 118
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Nuclear force
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Force of attraction that holds nucleus together
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Nuclear binding energy
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Energy produced when atoms nucleons are bound together, energy released when a nucleus is formed from nucleons
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Band of stability
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Stable isotopes fall into a narrow band
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Radioactive tracer/label
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If you replace one atom with radioisotope- monitor radioactive emissions
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Radiation therapy
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Damage DNA of cancer cells
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External beam radiation therapy
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Delivered by machine
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Internal radiation (brachytherapy)
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Substance introduced to body
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Nonionizing radiation
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Light, microwaves

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