III Atomic Theory - III Atomic Theory Democritus All matter...

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Unformatted text preview: III Atomic Theory Democritus All matter consists of very small indivisible particles atomes [Greek for indivisible] Daltons Atomic Theory (beginning of the modern era of chemistry Postulates Elements composed of small particles called atoms. All atoms of a given element are identical (size, mass, chemical properties) and can not be changed into another element Compounds made up of more than one element. Ratio of the number of atoms of the element is an integer or simple fraction Chem reaction involves only separation, combination, or rearrangement of atoms. It does not result in creation or destruction Daltons New Theory supported the mass laws Mass Laws Law of Conversation of Mass Matter can not be created or destroyed Prousts Law of Definite Proportion [Constant Composition] Different samples of the same compound always have the same elements in the same ratio Law of Multiple Proportions If two elements can combine to form more than one compound, the masses of one element with a fixed mass of the second are in a ratio of small whole numbers It is found that 14 grams of nitrogen, can react with 16 grams of oxygen, 32 grams of oxygen and 40 grams of oxygen. This is evidence of of the law of? A) Constant composition B) Conservation of mass C) Multiple proportions It is found that 14 grams of nitrogen, can react with 16 grams of oxygen, 32 grams of oxygen and 40 grams of oxygen. This is evidence of of the law of? Law of Multiple Proportions If two elements can combine to form more than one compound, the masses of one element with a fixed mass of the second are in a ratio of small whole numbers Discovery of Particles Smaller than the Atom Crookes Cathode Rays When current applied, the tube begins to glow. Flow goes from cathode to anode. Called CATHODE RAYS Same beam occurs no matter what the gas. Therefore, cathode rays are part of every atom. Beams deflected in a magnetic field, so, they have negative charge Term electron coined by Stanley in 1891. Cathode rays are beams of electrons Gas filled tube cathode anode Mass to charge ratio (1897) Thomson Thomson used a Crookes tube and placed it in an adjustable magnetic field. He was able to determine the mass to charge (m/e) ratio of the cathode rays. By comparing the ratio to the smallest mass to charge ratio in solution discovered that the mass of the cathode ray had to be 1/1000 the mass of hydrogen atom. Therefore, contrary to Daltons hypothesis, there were particles smaller than the atom....
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This note was uploaded on 03/01/2009 for the course CHEM 103 taught by Professor Kramer during the Fall '08 term at University of Delaware.

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III Atomic Theory - III Atomic Theory Democritus All matter...

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