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lecture2 - CHAPTER 2 Atoms Molecules and Ions 2.1 The Early...

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2 - 1 CHAPTER 2: Atoms, Molecules, and Ions 2.1 The Early History of Chemistry Greeks (400 BC) Aristotle - earth (cold, dry), air (wet, hot), fire (hot, dry), water (wet, cold) Democritus - atomos 2000 years of alchemy and medicine based on Aristotelian theories metallurgy Robert Boyle (1627-91) Joseph Priestley – discovered oxygen 2.2 Fundamental Chemical Laws Antoine Lavoisier, father of modern chemistry - proved combustion involved combination with oxygen. Proposed Law of Conservation of Mass - mass is neither created nor destroyed. Joseph Proust - Law of Definite Proportion - a compound always contains the same elements in the same proportion by mass. John Dalton - Law of Multiple Proportions – 1803 - when two elements combine to form more than one compound, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. Ferrous Chloride, 44.06% Fe, 55.94% Cl and Ferric Chloride 34.43% Fe, 65.57% Cl g Cl/1 g Fe = 55.94 g Cl 44.06 g Fe = 1.2696 g Cl/1 g Fe = 65.57 g Cl 34.43 g Fe = 1.9044 ratio of masses = 1.9044 1.2696 = 1.5 1 = 3 2 water, 11.11% H, 88.89% O and hydrogen peroxide, 5.88% H, 94.12%O g O/1 g H = 88.89 g O 11.11 g H = 8.00 g O/1 g H = 94.12 g O 5.88 g H = 16.00 ratio of masses = 16.000 8.00 = 2 1 2.3 Dalton's Atomic Theory (1808) 1. Elements are made up of indivisible particles called atoms. 2. Atoms of the same element are identical, and atoms of different elements are different. 3. Atoms combine to form compounds in fixed integer ratios. 4. In chemical reactions, the atoms do not change. Dalton created the first table of atomic weights, based on the relative amounts of one element that combined with another. H was assigned a value of 1
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Chapter 2
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