Unit 7 – atomic structure

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democritus
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“atoms are tiny, indivisible, and indestructible” not based on scientific method
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Dalton’s atomic theory
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1. all elements are made of tiny indivisible particles called atoms 2. atoms of same element are identical. atoms of one element are different from those of another element 3. atoms of different elements can physically mix together or can chemically combine in simple whole-number rations to form compounds 4. chemical reactions occur when atoms are separated, joined, or rearranged. atoms of one element are never changed into atoms of another element
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atom
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smallest particle of an element that retains that element’s properties
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scanning tunneling microscopes
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observe individual atoms nanotechnology
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thomson
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discovered negatively charged subatomic particles (electron) using a cathode ray, determined charge to mass ratio for electrons
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cathode ray tube experiment
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magnet deflects cathode ray, charged metal plates deflect cathode ray, (+) plate attracts, (-) plate repels, the ray is a stream of negative particles (election), didn’t matter what type of gas or metal was used in the electrodes so electrons must be in all atoms
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Milikan
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determined charge of an electron (-1), used charge and charge to mass ratio from Thomson to calculate the mass of an electron
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thomson’s plum pudding model
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the atom is a uniform, positively charged sphere, with electrons stuck in it; like a chocolate chip cookie: dough is positively charged sphere and chips are electrons
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Rutherford’s gold foil experiment
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tested plum-pudding model: shot heavy, positively charged particles at thin sheet of gold and expected the particles to be very slightly deflected; most alpha particles went straight through (no deflection), some bounced straight back
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Rutherford
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discovered atoms are mostly empty space, all the positive charge and mass of the atom are in the nucleus, established the nuclear atom
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Eugene Goldstein
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observed a positively charged particle (protons: positively charged, about 2,000 x more mass than an electron) in cathode ray tubes
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James Chadwick
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discovered the neutrons: no charge, but mass equal to proton’s mass
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e-
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symbol of electron
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p
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symbol of proton
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n
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symbol of neutron
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1-
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charge of electron
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1+
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charge of proton
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1/1840
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relative mass of electron
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1+
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relative mass of proton
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bohr model of the atom
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an electron moves around the nucleus only in certain allowed circular orbits
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atomic number
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number of protons, identifies the element, # protons = # electron in a neutral atom
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isotopes
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atoms with the same number of protons but different number of neutrons
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mass number
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protons + neutrons
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average atomic mass
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weighted atomic mass of all the isotopes of that element it reflects mass and relative abundance of the isotopes as they occur naturally

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