Developing the atomic model

• Who suggested that all matter is made from atoms in 1803?

  John Dalton
• What was significant about Dalton's model of atoms compared to previous suggestions?

  Dalton's model was more detailed and explained evidence from his experiments on gases
• What did Dalton propose about all atoms of an element?

  All atoms of an element are identical
• What did Dalton state about different elements?

  Different elements contain different types of atom
• What did Dalton imagine atoms to be like, given the technology of his time?

  He imagined them as solid balls
• Who discovered the first subatomic particle and in what year?

  J.J. Thomson discovered the electron in 1897
• What did Thomson conclude about cathode rays in his experiments?

  He concluded that cathode rays were tiny negatively charged particles much smaller than atoms
• What did Thomson state about atoms in relation to electrons?

  Atoms contain electrons
• What did Thomson assert about the overall charge of atoms?

  Atoms are neutral overall
• What is Thomson's plum pudding model of the atom?

  • Atoms are spheres of positive charge
  • Electrons are dotted around inside, like pieces of fruit in a cake
• Who worked with Rutherford to test the plum pudding model?

  Hans Geiger and Ernest Marsden
• What was the purpose of Rutherford's experiment in 1909?

  To test the plum pudding model of the atom
• What did the scientists expect to happen when they pointed beams of positively charged particles at the gold foil?

  They expected the particles to go straight through the foil
• What unexpected result did Rutherford's experiment reveal about the alpha particles?

  Many particles changed direction slightly, and some came straight back
• How did Rutherford explain the results of his experiment?

  He suggested that an atom has a positively charged nucleus containing most of its mass
• What analogy did Rutherford use to describe the arrangement of electrons in an atom?

  Electrons orbit like planets in a solar system
• What did Niels Bohr realize about orbiting electrons and their behavior around the nucleus?

  They would be attracted to the oppositely charged nucleus and would spiral inwards
• What did Bohr use in 1913 to improve Rutherford's model of the atom?

  Mathematical models
• What concept did Bohr introduce regarding the arrangement of electrons around the nucleus?

  Electrons occupy fixed energy levels, or shells