development of the model of the atom

• What does atomic theory propose about matter?

  Everything is made of tiny, indivisible particles
• Who originally proposed atomic theory?

  Democritus
• How long after Democritus did Dalton improve on atomic theory?

  About 2300 years
• What did John Dalton describe atoms as?

  Solid spheres
• What was J.J. Thompson's contribution to atomic theory?

  He proposed the plum pudding model
• What did Thompson's experiments reveal about atoms?

  Atoms contain negatively charged particles
• What year did J.J. Thompson propose the plum pudding model?

  1897
• What did Rutherford's experiments with alpha particles demonstrate?

  Atoms have a compact nucleus
• What did Rutherford use in his experiments?

  Positively charged alpha particles
• What was the expected outcome of Rutherford's gold foil experiment?

  Alpha particles should pass through gold
• What unexpected result occurred in Rutherford's experiment?

  Some alpha particles were deflected
• What did Rutherford propose after his experiment?

  The nuclear model of the atom
• What flaw did Rutherford's model have?

  No explanation for electron stability
• Who proposed a solution to Rutherford's model flaw?

  Niels Bohr
• How did Bohr suggest electrons behave?

  Electrons orbit the nucleus in shells
• Why is Bohr's model important?

  It prevents the atom from collapsing
• What particles did Rutherford discover in the nucleus?

  Protons
• What did James Chadwick provide evidence for?

  Neutral particles called neutrons
• What are the key developments in atomic theory?

  • Democritus proposed atomic theory
  • Dalton described atoms as solid spheres
  • Thompson introduced the plum pudding model
  • Rutherford discovered the nucleus
  • Bohr suggested electron shells
  • Chadwick identified neutrons
• How did the understanding of the atom evolve over time?

  1. Democritus: Indivisible particles
  2. Dalton: Solid spheres for elements
  3. Thompson: Electrons in a positive sphere
  4. Rutherford: Nucleus with positive charge
  5. Bohr: Electrons in orbits around nucleus
  6. Chadwick: Discovery of neutrons