Chapter 3 Notes

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Chapter 3Notes
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Objectives

• SWBAT
• Compile information about scientists who helped
  develop the atom throughout history.
• Complete a scavenger hunt to search for Ch 3
  information

3
8 Scientists

• Democritus
• John Dalton
• J.J. Thomson
• Robert Millikan
• Ernest Rutherford
• Niels Bohr
• Werner Heisenberger
• Erwin Schrodinger

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Democritus
460 BC 370 BC, Greece Democritus was a Greek
philosopher who was one of two founders of
ancient atomist theory. The atomists held that
there are smallest indivisible bodies from which
everything else is composed, and that these move
about in an infinite void space. The atomists
held that there are two fundamentally different
kinds of realities composing the natural world,
atoms and void. Atoms, from the Greek adjective
atomos or atomon, indivisible, are infinite in
number and various in size and shape, and
perfectly solid, with no internal gaps Text
http//plato.stanford.edu/entries/democritus/ imag
e http//reich-chemistry.wikispaces.com/file/vie
w/demo._atom_model.gif/97847685/demo._atom_model.g
if
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John Daltons Atomic Theory of Matter

• 1766 1844, England
• 4 Postulates
• elements are composed of atoms
• all atoms of an element are identical, but
  different from atoms in other elements
• atoms are neither created nor destroyed
• a given compound always has the same relative
  number and kind of atoms.

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J.J. Thomson

• 1856 1940, England
• called the negative particles electrons
• determined the charge to mass ratio of an
  electron
• The Plum Pudding Model is Thomsons name for his
  model of the atom

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JJ Thomsons Plum Pudding Model of the Atom

• www.tamucc.edu

8

• Cathode Ray Tube (CRT)
• negative end is the cathode
• positive end is the anode
• A cathode ray is radiation streaming from a
  cathode to an anode in a CRT
• it is a stream of particles
• a magnet can deflect the ray
• cathode ray particles have a
• negative charge

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Cathode Ray Tube and Magnet Demo

• http//www.chem.uiuc.edu/clcwebsite/cathode.html

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Robert Millikan

• 1868 1953, US
• measured the charge of an electron using the Oil
  Drop Experiment.
• His experiment measured the force on tiny charged
  droplets of oil suspended against gravity between
  two metal electrodes.
• 1.60x10 -19 coulomb is the charge of an electron
• using Thomsons charge to mass ratio, he
  determined the mass of the electron
• is 9.11x10 -28 g

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Robert Millikans Oil Drop Experiment

• Robert Millikan
• received the Nobel
• Prize for his work
• www.68pair.com

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Ernest Rutherford

• 1871 1937, New Zealand
• Gold Foil Experiment (alpha scattering)
• he determined that an atoms positive charge,
  and most of its mass, was concentrated in the
  core
• (most of the atom is empty space)
• In 1920, Ernest Rutherford postulated that there
  were neutral, massive particles in the nucleus
  of atoms. 
• he named the core of the atom
• the nucleus

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Rutherfords Nuclear Model

• The atom contains a tiny dense center called the
  nucleus
• The nucleus is essentially the entire mass of the
  atom
• http//upload.wikimedia.org/wikipedia/commons/thum
  b/e/e1/Stylised_Lithium_Atom.svg/180px-Stylised_Li
  thium_Atom.svg.png

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Rutherfords Model of the Atom
The atom contains a tiny dense center called the
nucleus The nucleus is essentially the entire
mass of the atom
http//abyss.uoregon.edu/js/ast123/lectures/lec04
.html
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Rutherfords Gold Foil Experiment

• Alpha particles were directed at a sheet of gold
  foil.
• Over 98 of the particles went straight through
• Approx. 2 of the particles were deflected
• Approx. 0.01 of
• the particles bounced
• off the gold foil.
• www.sci.tamucc.edu

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Rutherfords Experiment

• www.sci.tamucc.edu

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Neils Bohr

• 1885 1962, Danish
• Bohr introduced the theory of electronstraveling
  in orbits around the atom's nucleus, the
  chemical properties of each element being
  largely determined by the number of electrons in
  the outer orbits of its atoms.
• Model is called the Planetary Model.
• Bohr also introduced the idea that an electron
  could drop from a higher-energy orbit to a lower
  one, in the process emitting a photon (light
  quantum) of discrete energy.

http//upload.wikimedia.org/wikipedia/commons/6/6d
/Niels_Bohr.jpg
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Neils Bohr

• Planetary Model of the Atom

• http//jila-amo.colorado.edu/research/images/bohr.
  gif

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Erwin Schrodinger

• 1887 1961, Austria
• Developed the Quantum Mechanical Model of the
  Atom.
• This is the current model of the atom.

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Quantum Mechanical Model
This image is a representation of Schrodingers
Quantum Mechanical Model of the atom. This model
shows the nucleus in the center surrounded by
electrons in different energy levels, but there
is no distinct energy level shown as in the Bohr
Model. http//www.physicalworld.org/restless_univ
erse/figs/fig_1_30.gif