Atomic Theories

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WHAT IS MATTER MADE OF?
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5 THEORIES OF MATTER
2. Tiny, solid particles called atoms
3. Lumps of positively charged material with
negative electrons all through it
3. A positive nucleus with negative electrons
moving around it
5. A positive nucleus with electrons orbiting
around it
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WHAT IS MATTER MADE OF?

• Empedocles was a Greek philosopher and scientist
• He said that matter is made of

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Why might that make sense to people who knew
nothing about atoms?
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HISTORY OF THE ATOM
Democritus develops the idea of atoms
460 BC
he pounded up materials in his pestle and mortar
until he had reduced them to smaller and smaller
particles which he called
ATOMA (greek for indivisible)
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SO WHAT IS MATTER MADE OF?

• John Dalton, who lived in the early 1800s, said
• Matter is made up of tiny particles called atoms
• Atoms cant be created, or destroyed
• All atoms of the same element are identical and
  are different from atoms of all other elements
• Different elements link together, in defined
  whole number ratios, to make compounds

Atoms are the smallest particles and dont have
distinct parts
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John Dalton, who lived in the early 1800s, said
1. Matter is made up of tiny particles called
atoms
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Dalton also said
2. Atoms cannot be created or destroyed
CREATED
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Dalton also said
3. All Elements have Unique Atoms
Lithium
Uranium
Gold
Sodium
Hydrogen
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Dalton also said
4. Elements combine in defined, whole number
ratios
H2O water
vs. not H2O
water
oxygen
oxygen
hydrogen
hydrogen
oxygen
oxygen
oxygen
½ hydrogen
hydrogen
hydrogen
hydrogen
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• Joseph John Thomson in 1897
• Discovered that atoms have negatively charged
  particles in them
• Concluded that since atoms are neutral they must
  also contain positive particles to balance the
  negatively charged particles
• Proposed that the atom is a lump of positively
  charged material with negative electrons all
  through it

Atoms arent the smallest particles and do have
distinct parts a positive body and electrons
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How Thomson Found Negative Particles

1. He used a cathode ray tube like these ones
2. The tubes contain small amounts of gas
3. He used electricity to run a current through the
   gas in the tube
4. The gas glowed
5. The glow started from the negative end and went
   to the positive end
6. Opposites attract so if the glow moved towards
   the positive end that meant it must have been
   negative
7. That meant some kind of negative things from the
   atoms were moving
8. We now call these particles electrons

High voltage Generator
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Production of Cathode Rays
Green Glow Starts Here
Green Glow Moves to Here
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• Ernest Rutherfords 1907 study of atomic
  structure
• He fired very tiny, fast, positive alpha
  particles at a very thin sheet of gold foil
• He expected the alpha particles to just pass
  straight through the spaces between the particles
  in the foil
• Some passed straight through, some veered off on
  angles, and some bounced back
• He concluded that atoms must have a positive core
  that the alpha particles were hitting
• He named this core the nucleus and proposed that
  the electrons revolved around the nucleus

Atoms arent the smallest particles and do have
distinct parts a positive nucleus and electrons
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Rutherfords Gold Foil Experiment
Apparatus for experiment
Path of alpha (a) particles
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• Neils Bohr in 1912 why dont negative electrons
  collapse into the positive nucleus?
• He thought Rutherfords model was fundamentally
  correct just not complete
• Something must be keeping the electrons from
  collapsing into the nucleus
• He determined that electrons only move in defined
  orbitals around the nucleus
• For electrons to move between orbitals they need
  specific amounts of energy
• He called these bundles of energy quanta

Atoms have distinct parts a positive nucleus and
electrons that revolve around it in orbitals
Bohr-Rutherford atom
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Evolution of the Atomic Model to be continued
Atomic Theorists on Teacher Tube videos
http//streaming.teachertube.com/viewVideo.php?tit
leAtomic_Theoristsvideo_id86254