The Development of the Model of the Atom

• What might lead to a scienrific model being changed or replaced?

  New experimental evidence.
• What was the belief about atoms before the discovery of the electron?

  Atoms were tiny spheres that could not be divided
• What did the plum pudding model suggest about the atom?

  The atom is a ball of positive charge with electrons
• What conclusion was drawn from the alpha particle scattering experiment?

  The mass of an atom is concentrated in the nucleus
• What model replaced the plum pudding model?

  The nuclear model of the atom
• Who adapted the nuclear model of the atom?

  Niels Bohr
• What did Niels Bohr suggest about electrons?

  Electrons orbit the nucleus at specific distances
• What idea emerged about the positive charge of the nucleus?

  It could be subdivided into smaller particles
• What name was given to the smaller particles of positive charge?

  Proton
• Who provided evidence for the existence of neutrons?

  James Chadwick
• How long after the nucleus became accepted was the neutron discovered?

  About 20 years
• What did the new evidence from the scattering experiment lead to?

  A change in the atomic model
• What are the main differences between the plum pudding model and the nuclear model of the atom?

  • Plum pudding model:
  • Atom is a uniform sphere of positive charge
  • Electrons are embedded within the sphere
  • Nuclear model:
  • Atom has a small, dense nucleus
  • Electrons orbit around the nucleus