science chapter 4: studying atoms

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Democritus
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-All matter consists of small particles that cannot be divided -Atoms: from greek word atoms meaning indivisible
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Aristotle
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-All matter made up of earth, air, fire and water -fire: hot/dry -water: cold/wet -No limit to the number of times you could divide the matter
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John Dalton
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-English, 18th century -studied behavior of gases in air -Determined that compounds have a fixed composition
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Dalton’s Theory
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-All atoms of the same element have the same mass, atoms of different elements have different mass -compounds contain atoms of more than one element Atoms in compounds always combine in the same ratio ***THIS THEORY HAS BEEN ALTERED TODAY
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Thomson
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English -when some materials are rubbed they attract other materials -these materials have a +/- charge -some charged particles can flow from one place to another (electric current) – he used a cathode ray tube (+and – metal at each end) and one outside the tube – A beam of electrons always bent toward + plate
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Thomson’s Model
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– Atoms are made of smaller particles – Plum Pudding a positive mass with negative charges scattered out. The + and – cancel each other out
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Rutherford’s Theory
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– U gives off fast moving + particles – Directed a student, Marsden, to shoot them at a sheet of gold
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Gold Foil Experiment
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– When A particles were shot at gold sheet, most went right through – some were deflected slightly – some bounced right back
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Rutherford’s Model
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Dense center with a + charge – atom is mostly empty space
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Subatomic Particles
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– PROTONS: found in nucleus; +1 charge, mass = 1 atomic mass unit (amu) – ELECTRONS: found outside nucleus, -1 charge, mass = 1/1863 amu (use 0) – NEUTRONS: discovered by chadwich, mass = 1 amu, o charge found in nucleus -protons and neutrons found in nucleus, electrons travel outside nucleus
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Atomic number
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number of protons in nucleus, also = number of electrons in an atom
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Mass number
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number of protons + number of neutrons in the nucleus; number of neutrons = mass number of – atoms number
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isotopes
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atoms of the same element that have the same atomic number but different mass number (same # of protons, different # of neutrons)
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Bohr’s Model
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Danish scientist – Nucleus surrounded by electrons – Model similar to solar system
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Enemy Levels
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-Areas around the nucleus where electrons ove – Electrons can move from levels to level be gaining or losing energy – When energy is lost, it may be seen as light
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Electron Cloud Model
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– Volume occupied by electrons – Cloud is denser where there are more electrons
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Atomic Oritals
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– Division of the cloud subdivision of energy levels – Place where electron is expected to be found -# of orbitals in every level = (#of level)
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Electron Configurations
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– Arrangement of electrons in the orbital – The most stable arrangement has electrons in the lowest energy levels (ground state) – When electrons are excited, they jump out to higher levels (excited state)

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