Changing Models of the Nucleus

• What did John Dalton propose about atoms?

  Atoms are the smallest constituents of matter
• How did Dalton describe atoms of different elements?

  They are different from one another
• What happens to atoms during chemical reactions according to Dalton?

  Atoms rearrange to form different substances
• What significant particle did J.J. Thomson discover?

  The electron
• What is the 'plum pudding' model proposed by Thomson?

  Atoms consist of positive and negative charges
• How did Thomson visualize the structure of the atom?

  As spheres of positive charge with electrons
• What was the aim of Rutherford's Gold Foil Experiment?

  To test the plum pudding model
• What unexpected result did Rutherford find in his experiment?

  Many alpha particles were deflected
• What does the Rutherford model state about atoms?

  Atoms are mostly empty space
• What is located at the center of an atom according to Rutherford's model?

  A positively charged nucleus
• Who improved upon Rutherford's model in 1913?

  Neils Bohr
• What is the 'planetary model of the atom' proposed by Bohr?

  Electrons orbit the nucleus like planets
• What did Bohr state about electron energy levels?

  Electrons occupy well-defined shells
• Who took Bohr's model further in 1926?

  Erwin Schrödinger
• What does Schrödinger's model calculate regarding electrons?

  The likelihood of finding an electron
• How is Schrödinger's model visually represented?

  As a nucleus surrounded by an electron cloud
• What did James Chadwick discover in 1932?

  The neutron
• What are the key models of the atom in chronological order?

  1. John Dalton's Model (1803)
  2. J.J. Thomson's Plum Pudding Model (1897)
  3. Rutherford's Model (1909-1911)
  4. Neils Bohr's Planetary Model (1913)
  5. Quantum Mechanical Model (1926)

  
• What are the main features of the Quantum Mechanical Model?

  • Nucleus surrounded by an electron cloud
  • Probability-based location of electrons
  • Electrons are not in fixed orbits
• What were the implications of Rutherford's Gold Foil Experiment?

  • Atoms are mostly empty space
  • Existence of a central nucleus
  • Disproved the plum pudding model