Atomic Theory Timeline

1
Atomic Theory Timeline

• Development of our understanding
• of the atom

2
Early Models

• Democritus was first to suggest atom in 4th
  century B.C.
• Daltons model was the Billiard Ball
• Atomic Theory
• Matter is composed of atoms
• Atoms are indivisible
• Atoms of a given element have same size, mass and
  chem props and are different from those of
  another element
• Different atoms combine in whole number ratios to
  form compounds and are separated, combined and
  rearranged in chem reactions
• Conservation of Mass

3
Early Models

• Thomson used the Cathode Ray determined atoms
  were made of particles
• Negative charges in atom
• Plum Pudding model
• Millikan used oil drop experiment
• Found mass and charge of an electron

4
Important discoveries

• Rutherford experimented with Gold Foil
• Found nucleus
• Discovered its positive charge and tiny size
• Electrons moving around the nucleus
• Came up with Nuclear Model

5
Moving Forward

• Bohr said electrons move in orbits
• Found in energy levels
• Explains bright-line spectrum
• Called Planetary Model
• But Bohr knew that it was flawed

6
What we believe now

• Orbital proposed by Schrödinger
• Describes most likely where electrons were
• Quantum mechanics new theory
• Electron Cloud model