Chpt2 - Chapter 2 Atoms, Molecules, and Ions Atomic Theory...

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Chapter 2 Atoms, Molecules, and Ions
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Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, put forth by John Dalton.
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Dalton’s Postulates Each element is composed of extremely small particles called atoms.
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Dalton’s Postulates 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.
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Dalton’s Postulates 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.
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Dalton’s Postulates Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.
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Law of Constant Composition Also known as the law of definite proportions. In a given compound, the relative numbers and kinds of atoms are constant.
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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.
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Law of Multiple Proportions If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers.
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The Discovery of Atomic Structure A number of experiments by different researchers led to the current model of the atom. It was discovered that the atom is composed of subatomic particles, some of which are charged Remember that like charges repel and opposite charges attract.
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The Electron Streams of negatively charged particles were found to emanate from cathode tubes. J. J. Thomson (British scientist) is credited with the discovery of the electron (1897).
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The Electron Thomson measured the charge/mass ratio of the electron to be 1.76 × 10 8 coulombs/g.
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Millikan Oil Drop Experiment Once the charge/mass ratio of the electron was known, determination of either the charge or the mass of an electron would yield the other.
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Millikan Oil Drop Experiment Robert Millikan (University of Chicago) determined the charge on the electron in 1909 to be 1.60 x 10 -19 C. The mass of the electron can be calculated given the charge and the charge to mass ratio.
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Radioactivity: Radioactivity is the spontaneous emission of radiation by an atom. Henri Becquerel discovered radioactivity by observing the spontaneous emission of radiation from a Uranium mineral.
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Radioactivity Three types of radiation were discovered and studied by Ernest Rutherford: α particles – positively charged, relatively heavy β particles – negatively charged, relatively light γ rays – no charge or mass, light rays
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The Atom, circa 1900: “Plum pudding” model, put forward by Thomson. Positive sphere of matter with
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This note was uploaded on 04/25/2008 for the course CHEM 131 taught by Professor Sykora during the Spring '08 term at S. Alabama.

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Chpt2 - Chapter 2 Atoms, Molecules, and Ions Atomic Theory...

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