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u3ohnotesf2005 - Unit 3: Atomic Structure Basics of the...

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Unit 3: Atomic Structure Basics of the Atom Particle Charge Location in the Atom Mass proton 1+ in nucleus ~1 a.m.u. neutron 0 in nucleus ~1 a.m.u. electron 1– orbits nucleus ~0 a.m.u. a.m.u. : unit used to measure mass of atoms atomic number : # of p + -- the whole number on Periodic Table -- determines identity of atom mass number : (# of p + ) + (# of n 0 ) To find net charge on an atom, consider p + and e . ion : a charged atom
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2 anion : a (–) ion cation : a (+) ion -- more e than p + -- more p + than e -- formed when -- formed when atoms gain e atoms lose e Descrip- tion Net Charge Atomic Number Mass Number Ion Symbol 15 p + 16 n 0 18 e 38 p + 50 n 0 36 e 128 Te 2– 18 e 1+ 39 Historical Development of the Atomic Model
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Greeks (~400 B.C.E.) Matter is discontinuous (i.e., “grainy”). Hints at the Scientific Atom ** Antoine Lavoisier: law of conservation of mass ** Joseph Proust (1799) law of definite proportions : every compound has a fixed proportion e.g., water……………………. .8 g O, 1 g H chromium (II) oxide…….13 g Cr, 4 g O ** John Dalton (1803) law of multiple proportions : When two different compounds have same two elements, equal mass of one element results in integer multiple of mass of other. e.g., water…………………….8 g O, 1 g H hydrogen peroxide…….16 g O, 1 g H e.g., chromium (II) oxide……13 g Cr, 4 g O chromium (VI) oxide…. .13 g Cr, 12 g O John Dalton’s Atomic Theory (1808)
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4 1. Elements are made of indivisible particles called atoms. 2. Atoms of the same element are exactly alike; in particular, they have the same mass. 3. Compounds are formed by the joining of atoms of two or more elements in fixed, whole number ratios. e.g., 1:1, 2:1, 3:1, 2:3, 1:2:1 Dalton’s was the first atomic theory that had evidence to support it. ** William Crookes (1870s) Rays causing shadow were emitted from cathode. The Thomsons (~1900)
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J.J. Thomson discovered that “cathode rays” are… …deflected by electric and magnetic fields …(–) particles “electrons” William Thomson (a.k.a., Lord Kelvin) Since atom was known to be electrically neutral, he proposed the plum pudding model . -- Equal quantities of (+)
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This note was uploaded on 11/09/2011 for the course CHEM 110 taught by Professor Sullivan during the Fall '10 term at BYU.

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u3ohnotesf2005 - Unit 3: Atomic Structure Basics of the...

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