CHEM_1017___ch.2 - Daltons Atomic Theory (1808) 1. Elements...

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Dalton’s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms . All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements. 1. Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same. 1. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions.
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8 X 2 Y 16 X 8 Y +
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Cathode Ray Tube
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J.J. Thomson, (1906 Nobel Prize in Physics)
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Benjamin Franklin (1706 – 1790) discovered electricity and the electrical nature of matter. John Thompson (1808) used cathode ray tubes to show that all matter contains electrons (negatively charged particles) All matter, as we find it in nature, is electrically neutral, therefore there must also be positively charged particles present to counteract the electrons. Postulated the existence of protons.
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Antoine Becquerel (1852-1908) a French physicist and his T.A. Marie Curie discovered radioactivity in uranium. Some elements spontaneously decompose to form other elements (transmutation) and in the process emit other high energy particles in the form of rays .
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Ernest Rutherford (1871-1937), a New Zealand physicist, bombarded thin metal foils with alpha particles emitted from a radioactive substance. momentum = mass x velocity Average velocity of emitted alpha particles: 1.6 x 10 7 m/sec = 36 million m.p.h. Had so much momentum, nothing could possibly stop them!!!
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Rutherford concluded that all of the positive charge and most of the mass of the atom must be concentrated in a very tiny region of space which he called the nucleus. D= M/V The density of the nucleus is extremely high because of its very small volume compared with the total volume of the atom Average nuclear density = 2.0 x 10 14 g/mL 13 1 10
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atomic radius ~ 100 pm = 1 x 10 -10 m nuclear radius ~ 5 x 10 -3 pm = 5 x 10 -15 m Rutherford’s Model of the Atom “If the atom is the Superdome, then the nucleus is a marble on the 50-yard line.”
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The Titanic 882 ft. long (almost 3 football fields) wt.= 46,328 tons “Mother of All Trash Compactors” Squeeze 5,083 Titanics into a volume of 1 mL – less than the size of a red bean
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Chadwick’s Experiment (1932) H atoms - 1 p; He atoms - 2 p mass He/mass H should = 2 measured mass He/mass H = 4 α + 9 Be 1 n + 12 C + energy neutron (n) is neutral (charge = 0) n mass ~ p mass = 1.67 x 10 -24 g
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Mass of atoms (extremely small) are measured on a relative scale with units called atomic mass units (a. m. u.). Particle
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CHEM_1017___ch.2 - Daltons Atomic Theory (1808) 1. Elements...

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