Unit07s_2

Unit07s_2 - Chem 003 Fall 2009 Historical background...

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Nuclear Chemistry Chem 003 – Fall 2009 Blackboard: http://blackboard.gwu.edu Office Hours: MW 3:10-3:55 PM, 1957 E street, room 213 or by appointment - Antoine Henri Becquerel (1895): Discovered Radioactivity by accident. - Marie Sklodowska (Becquerel's Polish grad student) came up with the name: Historical background - Marie married the French physicist Pierre Curie - Antoine, Marie and Pierre shared the Nobel prize in Physics in 1903 Radioactivity: spontaneous emission of radiation from certain unstable elements - Pierre died in 1906 - Marie won the Nobel prize again in 1911 - Marie Curie died in 1934 of leukemia, probably brought by her long exposure to radioactive materials - Frédéric and Irène Joliot-Curie discovered induced radioactivity and positron emission in 1934. They were awarded the Nobel prize in 1935 - The nucleus of an atom contains _________ and __________, and we collectively refer to these particles as __________. - Atoms of a given element all have the same number of protons (atomic number), but different _________ have different numbers of neutrons. Isotopes are distinguished by their mass numbers (total number of nucleons). Isotopes and Radioisotopes 6 11 C 6 12 C 6 13 C 6 14 C - Radioactive nuclei are called radionuclides. Atoms containing radionuclides are called radioisotopes. - Radionuclides spontaneously decay by emitting particles and electromagnetic radiation.
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Types of Radioactivity Name Mass (amu) Charge Velocity Alpha ( α ) 4 +2 He nuclei 0.1c Beta ( β ) 0.0005 -1 electrons <0.9c Gamma ( γ ) 0 0 High-energy electromagnetic radiation c c: speed of light (300,000 km/s) Radiation Change in Atomic Number Change in Mass Number Change in Number of Neutrons Alpha emission, 4 2 He -2 -4 -2 Beta emission, o -1 e +1 0 -1 Gamma emission, o o γ 0 0 0 Possitron emission, o +1 e -1 0 +1 Beta capture, o -1 e -1 0 +1 Chemical Reaction Nuclear Reaction Atoms retain their identity Atoms usually change from one element to another Reactions involve only electrons, and usually the outermost electrons Reactions involve mainly protons and neutrons. It does not matter what the valence electrons are doing Reaction rates can be speeded up by raising the temperature Reaction rates are unaffected by changes in temperature Energy absorbed or given of in reactions is relatively small Reactions sometimes involve enormous changes in energy Mass is conserved. The mass of the products equals the mass of starting material Huge changes in energy are accompanied by measurable changes in mass.
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β -decay 2 He + -1 e 1 H 33 o tritium β -decay 6 C 14 o + -1 e
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α -decay 94 Pu 239 92 U 235 4 + 2 He 2+ 94 p + 92 p + 2 p + 145 n 143 n 2 n alpha particle α -decay 88 Ra 226 4 + 2 He 2+ 88 p + 86 p + 2 p + 138 n 136 n 2 n
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6 C 11 5 B 11 o + +1 e Other nuclear reactions Positron emission 6 p + 5 p + 5 n 6 n Electron capture 6 C 11 5 B 11 o + -1 e 6 p + 5 p + 5 n 6 n Both, positron emission and electron capture decrease in 1 unit the atomic number with no change in mass number.
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Gamma ( γ ) radiation Gamma rays consist of high-energy photons (electromagnetic radiation of very short wavelength). It accompanies nuclear reorganization: 27 Co 60 Matter annihilation -1 e + +1 e2 o γ oo o
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This note was uploaded on 11/09/2010 for the course CHEM 003 taught by Professor Marting.zysmilich during the Fall '06 term at GWU.

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Unit07s_2 - Chem 003 Fall 2009 Historical background...

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