Chapter 3 Notes

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Chapter 3Notes

• (rev. 10/14/09)

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Democritus
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/ image http//reich-chemistr
y.wikispaces.com/file/view/demo._atom_model.gif/97
847685/demo._atom_model.gif
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• Atoms
• Smallest particle of an element that retains the
  chemical identity of
• that element.
• Principles of Chemical Behavior
• Lavoisier Law of Conservation of Matter
• Proust Law of Constant Composition
• a compound always contains the same elements in
  the same proportions by mass.

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John Daltons Atomic Theory of Matter

• 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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Michael Faraday

• atoms contain particles that have an electrical
  charge

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Ben Franklin

• studied electricity
• he determined the following
• there are 2 kinds of charge positive and negative
• 2 like charges repel each other
• opposites charges attract each other
• excess negative charge can be discharged as
  static electricity

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Ben Franklin

• Do you remember Ben Franklins famous kite
  experiment?

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J.J. Thomson

• 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

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

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Robert Millikan

• measured the charge of an electron using the Oil
  Drop Experiment.
• x-rays gave the oil a negative electron
• 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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Henri Becquerel

• discovered that uranium
• exhibits radioactivity
• the chemical properties
• of an element change as
• it gives off radiation

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Ernest Rutherford

• alpha particles have a 2 charge
• beta particles are high
• speed electrons
• gamma rays are not
• composed of particles

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Rutherford

• 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 Gold Foil Experiment

• 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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James Chadwick

• Chadwick proved the existence of neutrons.

http//dev.physicslab.org/img/c2df54c3-7f43-4f21-8
c54-36f23218c5f5.gif
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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

This is an image of a lithium atom.
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The Nucleus

• The nucleus is positively charged
• The amount of positive charge in the nucleus
  balances the negative charge of the electrons
• The electrons move around in the empty space of
  the atom surrounding the nucleus

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Neils Bohr

• Planetary Model of the Atom

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

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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