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14-2 Notes Atomic number-number of protons in the nucleus of an atom Uranium is heaviest naturally occurring element=92 protons Isotopes-atoms of the same element that have different numbers of neutrons Mass of the protons and neutrons make up the nuclear mass of the atom Carbon-12, Carbon-13, Carbon-14 If proton # = neutron # then it is a stable atom Mass number = proton # + neutron # Strong nuclear force--holds protons together in the nucleus Atomic nuclei are stable when proton number is = to neutron number (esp. true in larger nuclei—Pu, U) When the nucleus releases particles to become more stable, energy is given off. This is called radioactive decay. (release of particles and energy) Transmutation--changing of one atom into another because of release of protons Alpha particle—2 protons and 2 neutrons Americium-241 releases energy and particles called nuclear radiation (in smoke detectors- when electricity is disrupted the alarm sounds) A neutron can become unstable and turn into a proton and electron--beta decay H-3 (isotopes) goes through beta decay and 1 neutron turns into a proton, and electron. This causes it to be an isotope of He. Radioactive decay is random. Half-life—amount of time it takes for half of the nucleus of an atom to decay Carbon-14 has a half-life of 5730 yrs. Starting with 100 g of carbon-14, how much would be left after 17,190 yrs? _____________________________________ Radioactive decay of unstable atoms is unaffected by weather, pressure, magnetic or electrical fields, or chemical reactions C-14 (carbon-14) is used to determine the age of once living things (half life =5730 yrs) U-238 (uranium-238) is used in determining the age of rocks (half life=4.5 billion years) Nuclear waste is buried in Carlsbad, NM. 655 m underground Alpha and beta particles are smashed into other elements that can absorb them and form new elements Tracer elements are used to diagnose disease and study environmental conditions These isotopes have very short half-lives so organisms are not subjected to much radiation. I-131 is used to diagnose thyroid problems Radon-222 has a half-life of 3.8 days. Starting with 50 g of radon-222, how much would be left after 19 days?