Chemistry 8 - Chemistry 8/26/08 Significant Figures The...

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Chemistry 8/26/08 Significant Figures The term sig. figs refers to the digits that were measured When rounding calculated numbers we pay attention to sig. figs so we do not overstate the accuracy of our answers 1. All nonzero digits are significant 2. Zeroes between 2 sig figs are themselves significant 3. Zeroes at the beginning of a number are never significant 4. Zeroes at the end of a number are significant if a decimal point is written in the number. When addition or subtraction is performed, answers are rounded to the least significant decimal place When multiplication or division is performed, answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation Accuracy vs. Precision Accuracy refers to the proximity of a measurement to the true value of a quantity Precision refers to the proximity of several measurements to each other CHAPTER 2!!! ATOMS, MOLECULES, AND IONS Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early 19 th century, championed by John Dalton Daltons Postulates 1. Each element is composed of extremely small particles called atoms 2. All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements 3. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions 4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms Law Of Constant Composition—Joesph Proust Also known as the law of definite proportions The elemental composistion of a pure substance never varies Multiple Proportions….Law of Conservation of Mass The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place THE ELECTRON Streams of negatively charged particles were found to emanated from cthode tubes J.J. Thompson is credited with their discovery (1897) Thompson measured the charge/mass ratio of the electron to be ***** 1.76 x 10^8 coulombs/g Milikan Oil Drop Experiment Once the charge/mass ratio of the electron was known, determination of either the charge or mass of an electron would yield the other. Robert Milikan-determined the charge on the electron Radioactivity: The spontaneous emission of radiation by an atom Three types of radiation were discovered by Ernest Rutherford: o A particles o B particles o Y rays The Atom, circa 1900 “plum pudding” model, put forth by Thompson Positive sphere of matter with negative electrons imbedded in it Discovery of the Nucleus
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Rutherford shot alpha particles at a thin sheet of gold foil and observed the pattern of scatter of the particles. The Nuclear Atom
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This note was uploaded on 09/28/2008 for the course BIO 1020 taught by Professor Parish during the Spring '08 term at Auburn University.

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Chemistry 8 - Chemistry 8/26/08 Significant Figures The...

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