Lecture 16

Lecture 16 - Nuclear Chemistry Chapter 23 Nuclear...

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Unformatted text preview: Nuclear Chemistry Chapter 23 Nuclear Reac1ons and Their Applica1ons 23.1 Radioac0ve Decay and Nuclear Stability 23.2 The Kine0cs of Radioac0ve Decay 23.3 Nuclear Transmuta0on: Induced Changes in Nuclei 23.4 The Effects of Nuclear Radia0on on MaEer 23.5 Applica0ons of Radioisotopes 23.6 The Interconversion of Mass and Energy 23.7 Applica0ons of Fission and Fusion The Nucleus •  The nucleus is comprised of the two nucleons, protons and neutrons. •  The number of protons is the atomic number. •  The number of protons and neutrons together is effec0vely the mass of the atom. Radioac0vity •  Some nuclides of an element to be unstable, or radioac0ve. •  These nuclides are referred to as radionuclides. •  There are several ways radionuclides can decay into a different nuclide. Radioac1vity/Isotope/Radia1on Radioac1vity is the property by which atomic nuclei gives off radia1on Radioisotopes are isotopes that have an unstable nucleus. They emit radia1on to aGain more stable nucleus through radioac1ve decay. Radia1ons are the penetra1ng rays/par1cles emiGed by a radioac1ve source. Presence of too many or too few neutrons rela1ve to protons create an unstable nucleus An unstable nucleus loses energy by emiJng radia1on during radioac1ve decay Alpha Decay Types of Radioac0ve Decay Loss of an α ­par0cle (a helium nucleus) 4 2 He 238 92 U ȺȺ→ 234 90 4 2 Th + He Beta Decay Types of Radioac0ve Decay Loss of a β ­par0cle (a high energy electron) 0 −1 β 131 53 I ȺȺ→ 0 −1 e or 131 54 Xe + 0 −1 e Positron Emission Types of Radioac0ve Decay Loss of a positron (a par0cle that has the same mass as but opposite charge than an electron) 0 1 e 11 6 C ȺȺ→ 11 5 B + 0 1 e Gamma Emission Types of Radioac0ve Decay Loss of a γ ­ray (high ­energy radia0on that almost always accompanies the loss of a nuclear par0cle) 0 0 γ Electron Capture (K ­Capture) Types of Radioac0ve Decay Addi0on of an electron to a proton in the nucleus –  As a result, a proton is transformed into a neutron. 1 1 p + 0 −1 e ȺȺ→ 1 0 n Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Mass Number A Atomic Number Z proton 1p 1 or 1H 1 neutron 1n 0 X Element Symbol electron 0e  ­1 or α par0cle positron 0β  ­1 0e +1 or 0β +1 4He 2 or A 1 1 0 0 4 Z 1 0  ­1 +1 2 4α 2 Three types of radioac1ve emissions in an electric field. Types of Radioac1ve Decay: Balancing Nuclear Equa1ons Alpha decay  ­ A decreases by 4 and Z decreases by 2. Every element heavier than Pb undergoes α decay. Beta decay  ­ ejec0on of a β par0cle from the nucleus from the conversion of a neutron into a proton and the expulsion of 0 ­1β. The product nuclide will have the same A but will be one atomic number higher. Positron decay  ­ a positron (0 ­1β) is the an0par0cle of an electron. A proton in the nucleus is converted into a neutron with the expulsion of the positron. A remains the same but the atomic number decreases. Electron capture  ­ a nuclear proton is converted into a neutron by the capture of an electron. A remains the same but the atomic number decreases. Gamma emission  ­ energy release; no change in Z or A. Sample Problem 23.1 PROBLEM: Wri1ng Equa1ons for Nuclear Reac1ons Write balanced equa0ons for the following nuclear reac0ons: (a) Naturally occurring thorium ­232 undergoes α decay. (b) Zirconium ­86 undergoes electron capture. PLAN: Write a skeleton equa0on; balance the number of neutrons and charges; solve for the unknown nuclide. SOLUTION: (a) 23290Th 22888X + 42α A = 228 and Z = 88 232 Th 228 Ra + 4 α 90 88 2 (b) 8640Zr + 0 ­1e AZX A = 86 and Z = 39 86 Zr + 0 e 86 Y 40  ­1 39 ...
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This note was uploaded on 02/18/2012 for the course CHEM 6C taught by Professor Hoeger during the Spring '08 term at UCSD.

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