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Unformatted text preview: The Components of Matter 1 Principles of General Chemistry, 2 nd ed. By M. Silberberg Chemistry, 8th ed. by W. Whitten, R. Davis, R., M. L. Peck, and G. Stanley. Lecture Outline • Structure of atoms & fundamental particles • Atomic number, mass number & symbol • Isotopes and atomic masses • Changes in the nucleus • Radioactivity and nuclear stability • Radioactive decay and types • Balancing nuclear reactions • Kinetics of radioactive decay • Nuclear transmutation • Nuclear fission and fusion Fundamental Particles P a rtic le M a s s (a m u ) C h a rg e E le c tro n (e- ) 0 .0 0 0 5 4 8 5 8 -1 P ro to n (p ,p + ) 1 .0 0 7 3 + 1 N e u tro n (n ,n ) 1 .0 0 8 7 0 The Discovery of Electrons • Humphrey Davy in the early 1800’s passed electricity through compounds and noted: – that the compounds decomposed into elements. – concluded that compounds are held together by electrical forces. • Michael Faraday in 1832-1833 realized that the amount of reaction that occurs during electrolysis is proportional to the electrical current passed through the compounds. The Discovery of Electrons • Cathode Ray Tubes experiments performed in the late 1800’s & early 1900’s. – Consist of two electrodes sealed in a glass tube containing a gas at very low pressure. – When a voltage is applied to the cathodes a glow discharge is emitted. The Discovery of Electrons • These “rays” are emitted from cathode (- end) and travel to anode (+ end). – Cathode Rays must be negatively charged! • J.J. Thomson modified the cathode ray tube experiments in 1897 by adding two adjustable voltage electrodes. – Studied the amount that the cathode ray beam was deflected by additional electric field. The Discovery of Electrons The Discovery of Electrons • Thomson used his modification to measure the charge to mass ratio of electrons. Charge to mass ratio e/m = -1.75881 x 10 8 coulomb/g of e- • Thomson named the cathode rays as electrons. • Thomson is considered to be the “discoverer of electrons” . • TV sets and computer screens are cathode ray tubes. The Discovery of Electrons • Robert A. Millikan won the 1 st American Nobel Prize in 1923 for his famous oil-drop experiment. • In 1909 Millikan determined the charge and mass of the electron. The Discovery of Electrons • Millikan determined that the charge on a single electron = -1.60218 x 10-19 coulomb . • Using Thomson’s charge to mass ratio we get that the mass of one electron is 9.11 x 10-28 g. – e/m = -1.75881 x 10 8 coulomb – e = -1.60218 x 10-19 coulomb – Thus m = 9.10940 x 10-28 g Canal Rays and Protons • Eugene Goldstein noted streams of positively charged particles in cathode rays in 1886....
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This note was uploaded on 07/24/2011 for the course CHEM 16 taught by Professor Siao during the Spring '07 term at University of the Philippines Diliman.
- Spring '07