1.7 The History of The Atom

• What is the main topic of the video discussed in the study material?

  The history of the atom
• What does atomic theory propose about matter?

  Everything is made up of tiny particles that cannot be broken down further
• Who originally proposed the atomic theory?

  Democritus
• When did Democritus live?

  Around 500 BC
• What did John Dalton describe atoms as?

  Solid spheres
• What did Dalton suggest about different types of spheres?

  They might make up different elements
• What model did J.J. Thompson propose in 1897?

  The plum pudding model
• What did Thompson's experiments show about atoms?

  Atoms cannot be solid spheres and contain negatively charged particles
• What are the negatively charged particles in atoms called?

  Electrons
• What did Ernest Rutherford discover in 1909?

  That atoms have a compact nucleus containing positive charge
• What experiment did Rutherford conduct to test the plum pudding model?

  He fired positively charged alpha particles at a thin sheet of gold
• What was the expected outcome of Rutherford's experiment if the plum pudding model was correct?

  The alpha particles should pass right through the gold sheet
• What unexpected result did Rutherford observe in his experiment?

  Some alpha particles were deflected to the side and some were deflected back
• What did Rutherford propose based on his experimental results?

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

  It did not explain why electrons do not collapse into the nucleus
• Who proposed that electrons orbit the nucleus in 1913?

  Niels Bohr
• How did Bohr's model prevent the atom from collapsing?

  Electrons orbit the nucleus in shells
• What has supported Bohr's model over the years?

  Many experiments
• What did Rutherford discover about the nucleus later on?

  The positive charge in the nucleus is made up of protons
• Who provided evidence for neutral particles in the nucleus?

  James Chadwick
• What are the neutral particles in the nucleus called?

  Neutrons
• What are the key developments in the history of atomic theory?

  • Democritus proposed atomic theory (500 BC)
  • John Dalton described atoms as solid spheres
  • J.J. Thompson introduced the plum pudding model (1897)
  • Ernest Rutherford discovered the nucleus (1909)
  • Niels Bohr proposed electrons orbiting the nucleus (1913)
  • James Chadwick identified neutrons
• How did the understanding of atomic structure evolve over time?

  1. Democritus: Matter is made of indivisible particles
  2. Dalton: Atoms as solid spheres
  3. Thompson: Atoms contain electrons (plum pudding model)
  4. Rutherford: Nucleus contains positive charge
  5. Bohr: Electrons orbit in shells
  6. Chadwick: Discovery of neutrons