Studying The Atom

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Studying The Atom
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Matter is made of atoms
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Models

• Models are often used for things that are too
  small or too large to be observed or that are too
  difficult to be understood easily

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Models

• In the case of atoms, scientists use large models
  to explain something that is very small
• Models of the atom were used to explain data or
  facts that were gathered experimentally.
• So, these models are also theories

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Early Models of the Atom Democritus

• Universe was made of empty space and tiny bits of
  stuff
• Called these tiny bits of stuff atomos (meaning
  uncut or indivisible)
• Atoms could not be divided

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Aristotle

• Did not think there was a limit to the number of
  times matter could be divided
• All substances built from 4 elements earth,
  air, fire, and water
• These elements are a combination of 4 qualities
  hot, cold, dry, and wet

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Dalton

• Did experiments that showed that elements in a
  compound always joined in the same way
• Hydrogen and oxygen always combine in a 21 ratio
  to form water
• Also observed gases and how they exert pressure
• Concluded that a gas consists of individual
  particles

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Dalton Atomic Theory

• All elements are composed of indivisible
  particles (atoms).
• Atoms of the same element are the same
• Atoms of different elements are different.
• Compounds contain atoms of more than one element
• In a compound, atoms of different elements always
  combine in the same way

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Thomson

• Using a glass tube with metal disks at each end
  and an electrical charge, he was able to isolate
  negatively charged particles
• No matter what type of metal he used, he always
  got the same charged particles (had the same
  mass)
• First to prove that atoms are made of even
  smaller particles

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Thomson

• Plum pudding model
• Atom made of a positively charged material with
  the negatively charged electrons scattered
  through it.
• The negative and positive charges balance each
  other

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Rutherford

• Gold Foil Experiment
• Hypothesized when alpha particles aimed at gold
  foil, that beams of light would deflect slightly
• What actually happened was many particles were
  deflected by more than 90 degrees or bounced
  straight back
• The deflection was created by interaction with a
  dense center of the atom the nucleus

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Rutherford

• Mostly empty space
• Small, positive nucleus
• Contained protons
• Negative electrons scattered around the outside