Chapter 02 notes S10

Chapter 02 notes S10 - 1 Chapter 2 Atoms Molecules and Ions...

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1 Chapter 2 Atoms, Molecules, and Ions
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2 The Atomic Theory Proof atoms exist Laws of Chemical Combination
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3 Law of Conservation of Mass Total mass is constant during a chemical reaction Mass of reactants must exactly match mass of products 2lbs potatoes + 3 ounces milk+ 1 ounce butter = 2.25 lbs mashed potatoes Also called a mass balance 11.1g H 2 (g) + 88.9g O 2 (g) = 100.0 g H 2 O (l) No matter can be created or destroyed
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4 Law of Definite Proportions All samples of a compound have the same chemical composition Same mass proportions & atomic ratios of elements present Also called “Law of Constant Composition” 8 Water molecules 16H + 8O 8H 2 O Each product formed from definite proportions of reactants. 1 Sundae formation: 2scoops + 1 cherry + 50ml 1 sundae
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5 Law of Multiple Proportions When 2 different compounds made of the same 2 elements are compared, the masses of one element combines with a fixed mass of the second element. The combination is in a ratio of small whole numbers . Open face sandwich 1 bread + 1 filling 1:1 ratio Regular sandwich 2 bread + 1 filling: 2/1 2:1 ratio Compounds are formed when atoms of different elements unite in fixed proportions
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6 Atomic Theory of Matter Hypotheses were derived from 3 Laws of Chemical Combination 1. All matter is composed of tiny particles called atoms 2. All atoms of a given element are identical, but atoms of different elements differ in size, mass and chemical properties Fluorine 18 amu Hydogen atom 1 amu 3. Compounds are formed when atoms of different elements unite in fixed proportions. 4. A chemical reaction involves atomic rearrangement . No atoms are created or destroyed F H F F F F F H F F H H F H + + 74amu = 72amu + 2amu 38amu + 36amu = 74amu
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7 Structure of the Atom What’s on the inside
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8 The Electron and Cathode Rays (1890’s) Electricity causes glow in tube at near vacuum Few molecules: minimal molecular interference Invisible ray causes coating on glass to glow Applied magnetic field or electric field deflects ray Ray is attracted to positively charged anode, so it must be made of negatively charged particles
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9 Numerical Values for Atomic Particles J.J. Thomson Ratio of cathode ray particle’s charge to mass charge/m e = –1.76 X 10 8 C/g Negatively charged particle is called an electron Robert Millikan Value for the charge on an electron e = -1.602 X 10 -19 C Value for the mass of an electron m e = (-1.602 X 10 -19 C) / (–1.76 X 10 8 C/g) m e = 9.10 x 10 -28 g
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10 Positively charged sphere with electrons imbedded inside “Raisin pudding model” Hydrogen atom 1 electron at the center of a sphere Helium atom: 2 electrons along a straight line Applied this analysis to atoms with up to 100 electrons The Atom: J. J. Thomson’s Model
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