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MATTER Insert united streaming video introtochem.asx Atomic Structure The Atom Insert united streaming video The_Atom.asf Continuous Theory of Matter Early Greeks Matter could be divided into smaller and smaller bits and still have the same properties. Discontinuous Theory of Matter Democritus and Leucippus Matter can only be divided so small and still have the same properties. “Atomos” meaning indivisible Followers “atomists” John Dalton’s Theory of the Atom •All matter is composed of atoms which are indivisible. •All atoms of the same element are exactly alike. •Atoms of different elements are different. •Compounds are formed by joining 2 or more elements in a definite whole-number ratio. J.J. Thomson’s Atomic Model “Plum Pudding Model” Knew the atom was neutral Knew there were negative particles Inferred that there had to be positive particles + - +- + ++ _ Rutherford's Gold Foil Experiment Rutherford’s Gold Foil Experiment .fsu.edu/ http://micro.magnet electromag/java/rutherford/ Ernest Rutherford’s Atomic Model The nucleus was a small dense center of the atom Most of the atom was made up of empty space Neil’s Bohr’s Atomic Model Protons and neutrons are in the small positively charged nucleus. Electrons are found in orbits or shells outside the nucleus Subatomic Particles location charge Mass Proton Nucleus Positive 1 AMU Neutron nucleus neutral 1 AMU electron Outside nucleus negative 1/2000 AMU Isotopes- atoms of the same element which have a different mass due to a different number of neutrons. Ex. C-12 C-14 #p = 6 #p = 6 #e- = 6 # e- = 6 #n = 6 #n=8 Isotopes will behave chemically the same because how they react depends upon their number of valence electrons. The difference is in how stable the nucleus is. The general rule is that the isotope will be radioactive if the # protons is not equal to the # neutrons. Which is most likely radioactive? C-12 or C-14 Because of all these scientists, we enjoy ..,