Chemistry Chapter 4

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ChemistryChapter 4

• Notes 1
• 09/10/10

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Democritus

• Matter is composed of empty space where atoms
  move
• Atoms are solid, homogenous, indivisible, and
  indestructible
• Different types of atoms have different sizes and
  shapes
• Differing properties of matter are due to the
  size, shape, and mvmt of atoms
• Apparent changes in matter result from changes in
  the groupings of atoms and not in changes in the
  atoms themselves

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Democritus

• 1st person to believe that matter was not
  infinitely divisible
• Just ideas no science (proof)
• 460 370 BC
• Completely rejected by Aristotle (did not believe
  in atoms)

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John Dalton

• 1766-1844
• English School Teacher
• Used science to prove Democritus ideas
• Beginning of modern atomic theory

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John Dalton

• All matter is composed of very small particles
  (atoms)
• All atoms of a given element are identical
  (having same mass, size, and properties)
• Atoms of a specific element are different from
  those of any other element
• Atoms cannot be created or destroyed or divided
  into smaller particles
• Different atoms combine in simple whole number
  ratios to form compounds
• In a chemical reaction, atoms are separated,
  combined, or rearranged

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Since Dalton.

• Modern atomic theory has been refined
• Atom
• Smallest particle of an element that retains the
  properties of that element

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Sir William Crookes

• Cathode ray typical set up used to study mass
  and charge of particles
• Crookes noticed flashes of light (radiation)
• He tested and proved
• Cathode rays were a steam of charged particles
• The particles had a negative charge
• After changing the electrodes and the gas in the
  tubes, the ray was still present, indicating that
  these particles were in all matter

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JJ Thomson Robert Millikan

• Continued with Crookes work
• Found that the mass of these particles was less
  than that of Hydrogen
• What did this mean?
• Something smaller than the atom!
• Atoms are divisible
• Millikan did work at the same time said these
  particles were negative called them electrons
• Thomson Proposed the Plum Pudding Model
• Positive atom with evenly dispersed negative

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Ernest Rutherford

• Disproved the plum pudding model with the gold
  foil experiment
• Rutherford set forth the idea of the nuclear atom
  (with a dense center)
• He called it a nucleus
• It has a positive change
• Almost all of the atoms mass
• Negatives charges surround the nucleus held
  together by attraction between pos. neg.
• 8 years later protons (1920)
• 1932 his coworker (Chadwick) discovered
  neutrons

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Neils Bohr

• In atomic physics, the Bohr model depicts the
  atom as a small, positively charged nucleus
  surrounded by electrons that travel in circular
  orbits around the nucleus similar in structure
  to the solar system, but with electrostatic
  forces providing attraction, rather than gravity.

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