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Transcript
Ch. 21 Nuclear Chemistry The Nucleus __________: Protons and neutrons. __________: an atom, identified by the number of protons and neutrons in its nucleus. Nuclides can be written with the name or symbol, followed by a dash with the mass number: ________________, or as follows: Atomic mass = 35 Atomic number = 17 Cl 21-2 The Nucleus ________________: the difference between the mass of an atom and the sum of the masses of its protons, neutrons and electrons. __________________: the energy released when a nucleus is formed from nucleons. ___________________: nucleons exist in different energy levels, or shells, in the nucleus. The numbers of nucleons that represent completed nuclear energy levels ~ 2, 8, 20, 28, 50, 82 and 126 are called Magic Numbers. 21-3 Radioactive Decay _______________: a reaction that changes the nucleus of an atom. ________________: a change in the identity of a nucleus as a result of a change in the number of its protons. Nuclear Particles Type Alpha particle Beta particle Positron Neutron Gamma Ray Symbol 4 He 2 0 β -1 0 β +1 1 n 0 γ Charge +2 -1 +1 0 0 21-4 Mass(amu) 4.0015062 0.0005486 0.0005486 0 Radioactive Decay 21-5 Radioactive Decay ___________________: the spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by emission of particles, electromagnetic radiation or both. _____________________: particles or electromagnetic radiation emitted from the nucleus during radioactive decay. ____________________: an unstable nucleus that undergoes radioactive decay. 21-6 Radioactive Decay _______________ (α): two protons and two neutrons bound together, emitted during some types of radioactive decay. 21-7 Radioactive Decay ___________________ (β): an electron emitted from the nucleus during some types of radioactive decay. 21-8 Radioactive Decay ______________ : a particle that has the same mass as an electron, but has a positive charge and is emitted during some types of radioactive decay. 21-9 Radioactive Decay ______________ (γ): high energy electromagnetic waves emitted from a nucleus as it changes from an excited state to a ground state. Example: Balance the following reaction: 212 Po → 4 He + ________ 84 2 Po → 42He + 20882 Pb 1) Balance the following reaction: 253 Es + 4 He → 1 n + ________ 99 2 0 212 253 84 99 Es + 42He → 10n + 256101 Md 21-10 Radioactive Decay ____________ : the time required for half the atoms of a radioactive nuclide to decay. 21-10 Radioactive Decay Example: Phosphorous-32 has a half-life of _______, how many milligrams of P-32 remain after ______________ if you start with a __________ sample? # of half-lives = time elapsed x 1 half-life = 57.2 days x 1 half-life 14.3 days 14.3 days = _____________ Amount of P-32 = original amount x # of half-lives = 4.0 mg x ½ x ½ x ½ x ½ = ____________ 21-12 Radioactive Decay 2) Polonium-210 has a half-life of 138.4 days, how many milligrams of Po-210 remain after 415.2 days if you start with a 2.0 mg sample? 21-13 Radioactive Decay Example: Assuming a half-life of _________, how many years will be needed for the decay of ________ of a given amount of radium-226? Amount remaining = 1/16 = 0.0625 = (½)4 = ____________ Years needed for decay of 15/16 = (1599 years) (__) = ___________ 21-14 Radioactive Decay 3) The half-life of radon-222 is 3.824 days, after what time will one-fourth of a given amount of radon remain? 21-15 Radioactive Decay ___________: a series of radioactive nuclide produced by successive radioactive decay until a stable nuclide is reached. 21-15 Radioactive Decay ______________: a very heavy nucleus splits into more stable nuclei of intermediate mass, starting a chain rxn. 21-17 Radioactive Decay _____________: low mass nuclei combine to form a heavier, more stable nucleus. 21-18 Ch. 21 The End!