Chapter_2-KW (1) - Chapter 2 Elements, Compounds and...

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1 Chapter 2 Elements, Compounds and Chemical Reactions
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2 Index 2.1 Elements and atoms are described by Dalton’s atomic theory 2.2 Atoms are composed of subatomic particles 2.3 The periodic table is used to organize and correlate facts 2.4 Elements can be metals, non-metals, or metalloids 2.5 Formulas and equations describe substances and their reactions 2.6 Molecular compounds contain neutral particles called molecules 2.7 Ionic compounds are composed of charged particles called ions 2.8 The formulas of many ionic compounds can be predicted 2.9 Molecular and ionic compounds are named following a system
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3 2.1. Elements and atoms are described by Dalton’s atomic theory 3 Chemical Laws The law of conservation of mass - in a chemical reaction, the mass of the reactants (starting materials) will equal the mass of resulting products § Implication: reactions involve the re-organization of materials. The law of definite proportions - the ratio of masses of each element is fixed for a given compound § Implication: Each atom has a fixed specific mass, thus in unique combinations, the mass ratio is specific
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4 2.1. Elements and atoms are described by Dalton’s atomic theory 4 Matter consists of tiny particles called atoms Atoms are indestructible. In chemical reactions, the atoms rearrange but they do not themselves break apart Dalton’s Atomic Theory
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5 2.1. Elements and atoms are described by Dalton’s atomic theory 5 Dalton’s Atomic Theory (Cont.) In any sample of a pure element, all the atoms are identical in mass and other properties. The atoms of different elements differ in mass and other properties. In a given compound the constituent atoms are always present in the same fixed numerical ratio. NaCl has a 1:1 atom ratio on the atomic level and larger
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6 2.1. Elements and atoms are described by Dalton’s atomic theory 6 The Law of Multiple Proportions When two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers. § Cements the idea that atoms react as complete (whole) particles. § Chemical formulas indicate whole numbers of atoms - not fractions
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7 2.1. Elements and atoms are described by Dalton’s atomic theory 7 Using The Law of Multiple Proportions sulfur sulfur dioxide trioxide Mass S 32.06 g 32.06 g Mass O 32.00 g 48.00 g Use these data to prove the law of multiple proportions
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8 2.2 Atoms are composed of subatomic particles 8 Discovery of the Electron by JJ Thomson In 1897, Thomson placed a magnet near CRT and noted deflection of the beam He repeated the experiment with an electrical field and noted that the discharge was deflected by an electrical field toward the (+) plate He announced the discovery of (-) particle, later named “electron” by Stoney
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9 2.2 Atoms are composed of subatomic particles 9 Rutherford’s Alpha Scattering Experiment Most alpha rays passed right through the Au A few were deflected off at an angle 1 in 8000 bounced back towards the alpha ray source
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Chapter_2-KW (1) - Chapter 2 Elements, Compounds and...

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