Ch. 2 - Chemistry: A Molecular Approach, 1st Ed. Nivaldo...

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Chapter 2 Atoms and Elements 2008, Prentice Hall Chemistry: A Molecular Approach , 1 st Ed. Nivaldo Tro Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA
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Tro, Chemistry: A Molecular Approach 2 Scanning Tunneling Microscope Gerd Bennig and Heinrich Rohrer found that as you pass a sharp metal tip over a flat metal surface, the amount of current that flowed varied with distance between the tip and the surface measuring this “tunneling” current allowed them to scan the surface on an atomic scale – essentially taking pictures of atoms on the surface
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3 Operation of a STM
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Tro, Chemistry: A Molecular Approach 4 Scanning Tunneling Microscope later scientists found that not only can you see the atoms on the surface, but the instrument allows you to move individual atoms across the surface
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Tro, Chemistry: A Molecular Approach 5 Early Philosophy of Matter Some philosophers believed that matter had an ultimate, tiny, indivisible particle Leucippus and Democritus Other philosophers believed that matter was infinitely divisible Plato and Aristotle Since there was no experimental way of proving who was correct, the best debater was the person assumed correct, i.e., Aristotle
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Tro, Chemistry: A Molecular Approach 6 Scientific Revolution in the late 16 th century, the scientific approach to understanding nature became established for the next 150+ years, observations about nature were made that could not easily be explained by the infinitely divisible matter concept
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Tro, Chemistry: A Molecular Approach 7 Law of Conservation of Mass in a chemical reaction, matter is neither created nor destroyed total mass of the materials you have before the reaction must equal the total mass of the materials you have at the end total mass of reactants = total mass of products Antoine Lavoisier 1743-1794
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Tro, Chemistry: A Molecular Approach 8 Reaction of Sodium with Chlorine to Make Sodium Chloride the mass of sodium and chlorine used is determined by the number of atoms that combine since only whole atoms combine and atoms are not changed or destroyed in the process, the mass of sodium chloride made must equal the total mass of sodium and chlorine atoms that combine together 7.7 g Na + 11.9 g Cl 2 19.6 g NaCl
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Tro, Chemistry: A Molecular Approach 9 Law of Definite Proportions All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements Joseph Proust 1754-1826
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Tro, Chemistry: A Molecular Approach 10 Proportions in Sodium Chloride 54 . 1 g 39.3 g 7 . 60 Na of mass Cl of mass = = a 100.0 g sample of sodium chloride contains 39.3 g of sodium and 60.7 g of chlorine a 200.0 g sample of sodium chloride contains 78.6 g of sodium and 121.4 g of chlorine 54 . 1 g 78.6 g 21.4 1 Na of mass Cl of mass = = a 58.44 g sample of sodium chloride contains 22.99 g of sodium and 35.44 g of chlorine 541 . 1 g 22.99 g 5.44 3 Na of mass Cl of mass = =
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This note was uploaded on 01/31/2011 for the course ACCT 2102 taught by Professor Clark during the Spring '10 term at Georgia State University, Atlanta.

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Ch. 2 - Chemistry: A Molecular Approach, 1st Ed. Nivaldo...

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