History of the atom

• Thomson's 'Plum Pudding' model:

  A) Positive Sphere

  B) Electrons

  
• Rutherford's Nuclear Model:

  A) Electrons

  B) Nucleus

  
• Rutherford's Gold Foil Experiment:

  1. Alpha particles (positively charged helium nuclei) were fired at the gold foil from a radioactive source.
  2. Most alpha particles passed straight through the foil, indicating that atoms are mostly empty space. However, some particles were deflected at large angles, and a very few even bounced back.

  Thus proving there is a dense nucleus at the centre of the atom

  
• Chadwick discovered neutrons by firing protons into a sample of Beryllium. He found that when they collided with an atomic nucleus, it was knocked out of its position.

  A) Nucleus

  B) Electron shells

  
• Chadwick discovered neutrons by firing protons into a sample of Beryllium. He found that when they collided with an atomic nucleus, it was knocked out of its position.
• Bohr's Model:

  1. Electrons orbit the nucleus at specific distances
  2. Electrons are emitted and absorbed at specific energies

  A) Nucleus

  B) Electron Shells