history of the atom

• What has changed over time regarding atomic models?

  They have evolved with improved experimental evidence
• Who presented the atomic theory in 1803?

  John Dalton
• What are the three key ideas of Dalton's atomic theory?

  Atoms are indivisible, identical for elements, combine to form substances
• What fundamental feature of science is illustrated by Dalton's theory?

  New evidence can change or replace scientific models
• What significant discovery did J.J. Thomson make in 1897?

  He discovered the electron
• What did Thomson's cathode-ray tube experiment prove?

  Atoms are divisible and contain electrons
• What model did Thomson propose based on his findings?

  The plum pudding model
• How did the plum pudding model depict the atom?

  Electrons spread throughout positively charged material
• What experiment did Rutherford conduct in 1909?

  The gold foil experiment
• What did Rutherford expect to happen in his gold foil experiment?

  Particles would pass through the foil
• What did Rutherford conclude from his gold foil experiment?

  Most of an atom's mass is in the nucleus
• How did Rutherford's findings change the atomic model?

  It led to the nuclear model of the atom
• What is the main difference between the plum pudding model and the nuclear model?

  Plum pudding has electrons in a positive sphere; nuclear has a nucleus
• What did Niels Bohr propose in 1913?

  Electrons orbit the nucleus in fixed shells
• What does each orbital in Bohr's model represent?

  A different energy level associated with electrons
• What question did Bohr's model answer regarding atomic structure?

  Why atoms do not collapse inwards
• What significant particle was discovered after Bohr's model?

  The proton
• When did Rutherford propose the existence of neutrons?

  In 1920
• Who provided evidence for the existence of neutrons in 1932?

  James Chadwick
• What experiment did Chadwick's evidence build upon?

  Frédéric and Irène Joliot-Curie's experiment
• What are the key developments in the history of atomic models?

  • Dalton's atomic theory (1803)
  • Thomson's plum pudding model (1897)
  • Rutherford's nuclear model (1909)
  • Bohr's model with fixed electron shells (1913)
  • Discovery of neutrons (1932)