Atoms

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Atoms
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400 b.c. Greeks

• Greeks philosophers ponder the nature of matter
  what is it made of?
• Democritus basic particle of matter atom
  which means indivisble.
• Envisions these to be hard spheres
• Aristotle does not believe in atoms

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Daltons Atomic Theory1803

• 1) All matter is composed of extremely small
  particles called atoms

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Daltons Atomic Theory1803

• Atoms of one element are all alike
• (size, mass)

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Daltons Atomic Theory1803

• 3) Atoms cant be created, destroyed or
  subdivided

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Daltons Atomic Theory1803

• Atoms of different elements combine in
• simple whole number ratios to form
• compounds

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Daltons Atomic Theory1803

• 5) In a chemical reaction, atoms are combined,
  separated, or rearranged

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Conservation of massin chemical reactions
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Conservation of massin chemical reactions
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1897 J.J. Thompson Cathode Ray Experiments

• The electron is discovered.
• PLUM PUDDING model

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Rutherfords Gold Foil Experiment1909

• Ernst Rutherford bombards a piece of gold foil
  with positively charged alpha particles (the
  nucleus of a helium atom)

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Some alpha particles bounce back
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Rutherfords Gold Foil Experiment

• Observations
• Most of the alpha particles passed straight
  through the gold foil as if it wasnt even there!
• The nucleus of the atom is small, dense, and
  positively charged

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Rutherfords Gold Foil Experiment

• Interpretation (conclusions)
• Atoms are mostly empty space and therefore MATTER
  is mostly empty space
• Atoms have a small, dense, positively charged
  nucleus

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This alpha particle passes through the
atoms empty space



Alpha particles have charge two charges will
repel each other
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Subatomic Particles(Table O)
Proton
Electron
Neutron
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Protons

• Located in the atoms nucleus
• Positive charge 1
• Mass 1 amu (Atomic Mass Unit)

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Neutrons

• Located in the atoms nucleus
• zero charge (neutral)
• Mass 1 amu (Atomic Mass Unit)

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Electrons

• Located in the electron cloud outside the nucleus
• Negative charge -1
• Mass 1/1836 amu (negligible)

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What are the subatomic particles in lithium and
carbon?
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Models of the atom
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A model of the atom to scale

• If YOU are the nucleus of an atom, your closest
  electron would be.
• ..in downtown Rhinebeck!

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Actual image of 2 atoms