Big Idea 1: Nuclear chemistry

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radioactivity
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property of matter in which unstable nucleus spontaneously emits small particles to attain stability (radioactive decay)
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radioactive isotope
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emit subatomic particles – electron (beta particle) – neutron – helium nucleus (alpha particle) – positron
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after emitting subatomic particles
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the nuclear mass and nuclear charge of the atom changes one isotope converted to another with a different identity -energy released in form of x-rays/gamma rays
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electrons/beta particles
electrons/beta particles
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collide less, usually do not penetrate skin
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neutrons
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emitted in nuclear reactions, very penetrating -easily pass through because of zero charge, significant damage because of mass
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helium nuclei/alpha particles
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travel few cm before colliding with air > lose KE > gain electrons > ordinary helium
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positrons
positrons
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positive equivalents to beta particles/electrons – unable to penetrate matter
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electron capture
electron capture
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proton + electron > neutron decreasing atomic number by 1
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gamma rays
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produced when some radioactive decay event occur -nucleus has excess energy > energy lost as gamma ray -no charge or mass, penetrate easily
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x rays
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highly penetrating electromagnetic radiation -penetrate body unless blocked by dense structure like bones
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natural radioactive elements
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polonium Z = 84 to uranium Z = 92 and potassium 40, vanadium 50, lanthanum 138
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transuranium elements
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92-118 artificial and radioactive
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hazards
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radon-222: potential environmental hazard, decomposition of uranium radium-226: biological damage uranium-238: hazards of radon gas potassium-40: light radioactive elements, emit positron to form argon-40
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half life
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half life of an isotope: 0.693/k fraction left: (1/2)^number of half-lives rate = KN K= constant N=number of radioactive nuclei Rate = number of nuclei that disintegrate per second ln (NÂș/N†) = Kt NÂș: original number of radioactive atoms N†: number of radioactive atoms left after t secs K: rate constant with units of s^-1 t: time in seconds from start of experiment

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