Development of the Atom

• What does atomic theory propose about matter?

  Everything is made of tiny 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 did Rutherford expect to happen in his gold foil experiment?

  Alpha particles should pass through
• What was the actual result of Rutherford's gold foil experiment?

  Some alpha particles were deflected
• What did Rutherford conclude from his experiment?

  Atoms have a compact nucleus
• What did Rutherford suggest about the negative charge in atoms?

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

  No explanation for electron stability
• 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 atoms?

  It prevents atoms from collapsing
• What did Rutherford discover about the nucleus later on?

  It contains protons
• What did James Chadwick provide evidence for?

  Neutral particles in the nucleus
• What is the current understanding of the atom's structure?

  • Atoms consist of a nucleus
  • Nucleus contains protons and neutrons
  • Electrons orbit the nucleus in shells
  • Electrons prevent the atom from collapsing
• What are the key historical models of the atom?

  1. Atomic theory by Democritus
  2. Solid spheres by John Dalton
  3. Plum pudding model by J.J. Thompson
  4. Nuclear model by Ernest Rutherford
  5. Planetary model by Niels Bohr