Development of atomic atom

• What does atomic theory propose about matter?

  Everything is made of tiny, indivisible particles
• Who originally proposed 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 make up different elements
• What model did J.J. Thompson propose in 1897?

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

  Atoms contain negatively charged particles
• How did Thompson describe the atom in his model?

  A ball of positive charge with electrons
• What significant experiment did Ernest Rutherford conduct in 1909?

  Fired alpha particles at gold foil
• What was Rutherford's expectation about alpha particles passing through gold?

  They should pass through without deflection
• What unexpected result did Rutherford observe in his experiment?

  Some alpha particles were deflected
• What conclusion did Rutherford draw from his experiment's results?

  Atoms have a compact nucleus
• What did Rutherford suggest about the arrangement of charges in an atom?

  Negative charge exists in a cloud around the nucleus
• What flaw did Rutherford's model have?

  Electrons should collapse into the nucleus
• Who proposed a solution to Rutherford's model in 1913?

  Niels Bohr
• How did Bohr suggest electrons orbit the nucleus?

  Like planets orbit the sun
• What did Bohr's model explain about atomic stability?

  Electrons in orbits prevent collapse
• What did further experiments by Rutherford discover about the nucleus?

  The nucleus contains protons
• What evidence did James Chadwick provide?

  Evidence for neutrons in the nucleus
• What are the key developments in atomic theory from Democritus to Chadwick?

  • Democritus: Proposed atomic theory (500 BC)
  • Dalton: Described atoms as solid spheres
  • Thompson: Plum pudding model (1897)
  • Rutherford: Nuclear model (1909)
  • Bohr: Electrons orbiting nucleus (1913)
  • Chadwick: Discovery of neutrons