Chapter 2 Lecture

Chapter 2 Lecture - Democritus of Abdera 460BC 370BC...

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1 Democritus of Abdera 460BC - 370BC • Quotations by Democritis I would rather discover one scientific fact than become King of Persia. Everything existing in the Universe is the fruit of chance and necessity. Nothing is so easy as to deceive one's self; for what we wish, that we readily believe. Nothing exists except atoms and empty space; everything else is opinion. Dalton’s Atomic Theory • English Chemist – (1766–1844) – Experimentalist • Explained the Law of Conservation of Mass • Tiny Indivisible Particles • Dalton’s Theory was a model for the Physical World 3 Dalton’s Atomic Theory Each element is composed of extremely small particles called atoms. 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 Section 2.1 atoms of one element are different from the atoms of all other elements. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in a chemical reaction. 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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2 4 Subatomic Particles Proton Neutron Section 2.2 Electron The Electron Streams of negatively charged particles were found to emanate from cathode tubes. Thompson measured the charge/mass ratio of the electron to be 1.76 × 10 8 coulombs/g. J. J. Thompson is credited with their discovery (1897). 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. Robert Millikan (University of Chicago) determined the charge on the electron in 1909.
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3 The Atom, circa 1900: “Plum pudding” model, put forward by Thompson. Positive sphere of matter with negative electrons imbedded in it. Radioactivity Three types of radiation were discovered by Ernest Rutherford: ± α particles ± β particles ± γ rays Discovery of the Nucleus Ernest Rutherford shot particles at a thin sheet of gold foil and observed the pattern of the pattern of scatter of the particles.
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4 The Nuclear Atom Since some particles were deflected at large angles angles, Thompson’s model could not be correct.
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This note was uploaded on 11/11/2009 for the course CHEM 1341 taught by Professor Compton during the Spring '08 term at Texas State.

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Chapter 2 Lecture - Democritus of Abdera 460BC 370BC...

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