Chap2 - Chem 200 Dr. Saidane Lecture Notes Chapter 2, Part...

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Chem 200 Dr. Saidane Lecture Notes Chapter 2, Part 1 Atoms Historical Development of the Model of the Nuclear Atom . A series of discoveries were made that led to the modern model of the atom. 1. In the late 1700, scientists studied chemical reactions and their discoveries led to three basic laws: a) The Law of Conservation of Mass , which states that mass is neither destroyed nor created during ordinary chemical reactions. b) The Law of Definite Proportions , which states that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound. c) The Law of Multiple Proportions , which states that, if two or more compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element, is always a ratio of small whole numbers. 2. In 1808 John Dalton proposed an explanation of the laws stated above. Dalton’s atomic theory can be summed up by the following statements: a) All matter is composed of extremely small particles called atoms. b) Atoms of a given element are identical in size, mass, and other properties. c) Atoms cannot be subdivided, created, or destroyed. This statement explains the law of conservation of mass. d) Atoms of different elements combine in simple whole-number ratios to form chemical compounds. This explains the law of definite proportion as well as the law of multiple proportions. 3. The modern atomic theory was developed between late 1800 and early 1900. During this period several scientists discovered that contrary to the third statement in Dalton’s theory, atoms could be subdivided in subatomic particles named electrons, protons and neutrons.
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a) Discovery of the electron . Several scientists investigated the relationship between electricity and matter. They performed several experiments using
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This note was uploaded on 09/09/2011 for the course CHEM 200 taught by Professor Saidane during the Spring '11 term at Mesa CC.

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Chap2 - Chem 200 Dr. Saidane Lecture Notes Chapter 2, Part...

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