development of the model of the atom

• what can lead to a scientific model being changed/replaced?

  new evidence
• what did John Dalton describe atoms as?

  tiny spheres that couldn't be divided
• what did JJ Thomson's discovery of the electron lead to?

  plum pudding model
• how did the plum pudding model describe an atom?

  the atom was a ball of positive charge w negative electrons embedded in it
• what did results from the alpha scattering experiment lead to?

  • most alpha particles passed through the gold foil so the mass of an atom was concentrated at the centre
  • some alpha particles were deflected so the atom has a positively charged nucleus
  • nuclear model
• how did Bohr adapt the nuclear model?

  suggested that electrons orbit the nucleus at specific distances
• what did further experiment lead to?

  • showed existence of protons
  • James Chadwick showed the existence of neutrons 20 years after the nucleus
• what is the difference between the plum pudding model & nuclear model?

  • the nuclear model is mostly empty space
  • in the nuclear model the positive charge is all in the nucleus
  • in the nuclear model the mass is concentrated in the nucleus
  • in the nuclear model the electrons orbit the nucleus