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~400 BC

Democitus

It took over 2000 years for these philosophers' error to be corrected...

1830

John Dalton

1906

Sir J.J. Thompson

So J.J Thompson showed that atoms contain electrons. This led to the "plum pudding" model of the atom

1909

Sir. Earnest Rutherford

Robert Millikan

1924

Neils Bohr

1920's

Werner Heisenberg

John Dalton

Werner Heisenberg

Sir Earnest Rutherford

  • Altered the model of the atom
  • Introduced the uncertainty principle
  • Proposed the region with high probability of finding the elecron
  • "Gold Foil" Experiment, shot positively charged, radioactive alpha particles at thin sheet of gold foil.
  • Proved the existence of a positively charged, small, dense nucleus.
  • Known as one of the fathers of chemistry
  • Developed the first rules of atomic theory
  • All matter is made of extremely small particles called atoms.
  • Atoms are indivisible and indestructible.
  • All atoms of a given element are identical in size, mass and properties.
  • Atoms of a specific element are different than those of another element.
  • Different atoms combine in simple whole number ratios to form compounds
  • In a chemical reaction, atoms are separated, combined or rearranged.
  • Two of these rules have since been proven incorrect, can you guess which ones?

Robert Millikan

  • "Oil Drop" Experiment
  • Used charged drops of oil
  • Discovered the charge and mass of the electron

Neils Bohr

Sir J.J Thompson

An Argument in the Ancient World

  • Observed light emitted from excited hydrogen atoms
  • Proposed that electrons "orbit" the nucleus in definite orbitals
  • Used a cathode ray (crooks) tube
  • Discovered the existence of electrons.
  • Determined the ratio of mass to charge for an electron
  • Determined that the mass of the electron was much less than the mass of the hydrogen atoms.
  • Electrons were subatomic particles.
  • Greek Philosopher Democritus proposed that there was a limit to how many times a piece of matter could be divided
  • He called the smallest piece of matter "atomos" meaning not to be cut.
  • He was dismissed due to lack of evidence.
  • Other philosophers views of 4 elements became favored.

The plum pudding model states that the electrons were lumpy relatively charged "plums" contained within a positively charged pudding

The History of Atomic Theory

By Abdullah, Ridhaa & Mukund

The Plum Pudding Model states that the electrons were lumpy, negatively charged "plums" contained within a positively charged pudding.

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