CHEM2 - Chapter 2 Atoms, Molecules, and Ions Fundamental...

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Chapter 2 Atoms, Molecules, and Ions
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Fundamental Laws The Law of Conservation of mass - In a chemical reaction, matter is neither created nor destroyed. The Law of Constant Composition (definite proportion) (by Joseph Proust). - The elemental composition of a pure substance never varies. The Law of Multiple proportions - When two elements (call them A and B) combine to two different compounds, the masses of element B that combine with 1 gram of element A can be expressed as a ratio of small whole numbers. e.g. CO; 1.33g O : 1g C CO 2 ; 2.67g O : 1g C The ratio is a small whole number (2.67g/1.33g = 2)
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Atomic Theory of Matter All of the atoms of a given element are identical. Different elements have different masses. A compound is a specific combination of atoms of more than one element. A chemical reaction consists of a reshuffling of atoms from one set of combinations to another; atoms are not created or destroyed. - John Dalton in 1803 1807 postulated the theory that atoms are the fundamental building blocks . - John Dalton (1766-1844): English Chemist, meteorologist, and physicist. - In 1794 published ‘Extraordinary facts relating to the vision of colors’ i.e. Color Blindness
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The Electron (Sir Joseph John Thomson in1897) Streams of negatively charged particles (smaller than atoms) were found to emanate from cathode tubes. Thompson measured the charge/mass ratio of the electron to be 1.76 × 10 8 coulombs/gram of electrons ). Properties: charged particles (e - ), deflected by electric and magnetic field; rays are same regardless of the source material
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Millikan Oil Drop Experiment Robert Millikan (University of Chicago) determined the basic charge on a single electron in 1909 (1.602 x 10 -19 C). Using the charge/mass ratio of the electron, the mass of a single electron could be calculated. A Nobel laureate in physics (1923) for his measurement of the charge on the electron and for his work on the photoelectric effect. g 10 x 9.10 C/g 10 x 1.76 C 10 x 1.60 Mass 28 8 19 - - = =
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Radioactivity The spontaneous emission of radiation by an atom. First observed by Henri Becquerel and also studied by Marie and Pierre Curie. Three types of radiation were discovered by Ernest Rutherford: α particles (+) β particles (-) γ rays (neutral)
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The Atom, circa 1900: “Plum pudding” model, put forward by Thompson. Positive sphere of matter with negative electrons imbedded in it.
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Discovery of the Nucleus Ernest Rutherford shot α particles at a thin sheet of gold foil and observed the pattern of scatter of the particles. - Father of nuclear physics - Nobel prize in chemistry in 1908
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The Nuclear Atom Since some particles were deflected at large angles, Thompson’s model could not be correct.
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Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom. Most of the volume of the atom is empty space.
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This note was uploaded on 04/20/2010 for the course CHEM 1030 taught by Professor Meda during the Spring '08 term at Auburn University.

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CHEM2 - Chapter 2 Atoms, Molecules, and Ions Fundamental...

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