Evolution of the Atomic Model

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Evolution of the Atomic Model
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Theories of Knowledge

• Empirical knowledge knowledge or statements
  based on observations
• The liquid boils at 100C
• Mixing these two chemicals produces a white
  solid
• Theoretical knowledge knowledge or statements
  based on theories
• Gas particles move in a random motion
• Hydrogen has 1 valence electron

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Greek Philosophers

• Democritus (5th century BC)
• All matter can be divided into smaller particles.
  He called this particle the atom.
• Many different kinds of atoms, each distinct in
  shape and size and that all atoms move around in
  space.

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Daltons Atomic Theory

• John Dalton (1803) postulated that
• All matter is made up of particles called atoms
• Atoms of each element were different from each
  other
• Atoms of two or more elements join together in
  fixed ratios to form new compounds (law of
  constant composition compounds have a fixed,
  definite proportion eg. H2O, CO2)
• Atoms are not destroyed in chemical reactions.
  They are rearranged. (law of conservation of mass
  matter is not created or destroyed)

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J.J. Thomson (1897)

• To find the make-up of an atom, he used a ray
  tube. He discovered there were negatively charged
  sub-particles ? electrons.
• Raisin Bun Model the atom is a () charged bun
  (mostly empty space) that contains (-) charged
  raisins (electrons) inside it.

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Ernest Rutherford (1911)

• Gold foil experiment shot () a particles
  through gold foil. Expected most will pass right
  through, but some particles were deflected at
  large angles.
• Determined that there was something in the middle
  of the atom
• An atom has a () core (nucleus) surrounded by
  empty space that also contains (-) electrons.
• In 1914, gave name proton for () sub-particle
  within atom

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James Chadwick (1932)

• Built upon Rutherfords work
• Discovered there were neutrally-charged
  sub-particles alongside with protons in atom ?
  called them neutrons

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Niels Bohr Planetary Model

• If protons are () and electrons are (-), we
  expect them to be attracted to each other. But
  this is not really the case why?
• Bohr discovered that the electrons of an atom
  exist in circular orbits (energy levels).
• Each energy level has an allowable of electrons.

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• Each orbit has a certain amount of energy. When
  an electron
• Moves to a higher orbit, it GAINS energy
• Moves to a lower orbit, it LOSES energy
• The outer-most electrons in an atoms orbit for
  an element is called the valence electron. The
  group numbers in the periodic table refers to how
  many VEs an element has!
• When the outermost orbit of an element is full,
  it is stable and generally non-reactive. This
  explains the properties of noble gases.