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Ch10 Sec1 Atoms & Atomic Theory
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atoms Smallest particles of matter All substances are made of atoms Atoms join with other atoms to make new substances
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How small is an atom? http://learn.genetics.utah.edu/content/begin/cells/scale/ Diameter = 0.000000001 cm
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Basic structure of all Atoms protons (p + ) are heavy, positively charged particles neutrons (n o ) are heavy particles with no charge (neutral) electrons (e - ) are extremely light, negatively charged particles electron cloud: region that occupies most of the volume of the atom nucleus: nucleus: small, dense region in the center of an atom which contains a majority of the mass
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Atoms are neutral Equal numbers of protons (+) and electrons (–) e - =7 p + =7
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The Elements: Each element has a different number of protons (atomic number) Ex: Fluorine 9FFluorine18.99 atomic number = number of protons symbol name average atomic mass (amu-mass of one atom) 92UUranium238.0
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Rutherford’s Gold Foil Experiment
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Discovery Most of the volume of an atom is empty space Nucleus contains heavy, positively charged particles (protons)
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Thomson Cathode-Ray Tube Discovery: Atoms contain negatively charged particles (electrons)
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Electrons Bohr discovered that electrons orbit the nucleus at different energy levels Electron cloud model –Region (orbital) where electrons are likely to be found
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Looking at atoms today… TEAM 0.5 world’s strongest transmission electron microscope at Lawrence Berkeley National Laboratory gold atoms forming between gold crystals
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