The History of the Atom

• What are atoms described as in the study material?

  Tiny particles of matter that make up everything in the universe
• Who described atoms as solid spheres at the start of the 19th century?

  John Dalton
• What did John Dalton say about different spheres?

  Different spheres made up different elements
• What conclusion did JJ Thomson reach about atoms in 1897?

  Atoms weren't solid spheres and contained smaller, negatively charged particles
• What are the negatively charged particles called that Thomson discovered?

  Electrons
• What was the new theory proposed by Thomson called?

  The 'plum pudding model'
• What did Rutherford's gold foil experiment demonstrate about the plum pudding model?

  It showed that the plum pudding model was incorrect
• What did Rutherford and his team expect to happen in the gold foil experiment?

  They expected the particles to pass straight through or be slightly deflected
• What did Rutherford conclude about the structure of the atom after his experiment?

  There is a tiny, positively charged nucleus at the center
• What surrounds the nucleus in Rutherford's nuclear atom model?

  A 'cloud' of negative electrons
• What problem did scientists identify with Rutherford's model regarding electron behavior?

  Electrons would be attracted to the nucleus, causing the atom to collapse
• What did Niels Bohr propose about the arrangement of electrons?

  Electrons exist in fixed orbits or shells
• What does each shell of electrons have according to Bohr's model?

  A fixed energy
• How was Bohr's theory of atomic structure received by the scientific community?

  It was supported by many experiments and explained other observations
• How has the current model of the atom changed from past models?

  It has evolved based on new evidence and experiments
• What role does peer review play in scientific research?

  It allows others to check for errors and develop their own work
• What are the key developments in the history of atomic theory?

  • John Dalton: Atoms as solid spheres
  • JJ Thomson: Discovery of electrons and the plum pudding model
  • Ernest Rutherford: Gold foil experiment and the nuclear model
  • Niels Bohr: Electrons in fixed orbits or shells
• How does scientific knowledge develop over time?

  • New evidence prompts modifications to existing theories
  • Ideas are tested through experiments
  • Peer review allows for error checking and further development