Gold foil experiment

• What did early theories suggest about the structure of atoms?

  Atoms were tiny solid spheres.
• What did J.J. Thomson discover in 1897?

  Electrons can be removed from atoms.
• What was Thomson's "plum pudding" theory?

  Atoms contain smaller bits with negative charges.
• What did Rutherford and Marsden's experiment reveal about alpha particles?

  Most passed through gold, some were deflected.
• What conclusion did Rutherford draw from his experiment?

  Most of the atom is concentrated at the center.
• What is the nucleus of an atom composed of?

  Protons and neutrons.
• How did Rutherford describe the space in an atom?

  Most of an atom is just empty space.
• What model did Rutherford's findings lead to?

  The nuclear model of the atom.
• What did Niels Bohr propose about electron orbits?

  Electrons exist in fixed orbits at set distances.
• What are the fixed distances where electrons exist called?

  Energy levels or shells.
• What is the Bohr model of the atom?

  Electrons exist in fixed orbits around the nucleus.
• What is the standard form for quantities related to atoms?

  A × 10ⁿ
• What does *n* represent in the standard form of atomic quantities?

  *n* is a positive integer between 1 and 10.
• What does *A* represent in the standard form of atomic quantities?

  *A* is a number between 1 and 10.
• What charge does the nucleus of an atom have?

  Positively charged.
• Where is most of the mass of an atom located?

  In the nucleus.
• How much smaller is the nucleus compared to the whole atom?

  About 10,000 times smaller.
• What do electrons do in relation to the nucleus?

  They whizz around in fixed orbits.
• What is the typical size of an atom?

  About 1 × 10^-10 m.
• What makes an atom neutral?

  The number of protons equals the number of electrons.
• What happens when an atom loses an electron?

  It becomes a positive ion (+ve).
• What happens when an atom gains an electron?

  It becomes a negative ion (-ve).
• What can atoms join together to form?

  Molecules.
• What is an example of a small molecule?

  Molecules of oxygen gas (O₂).
• What is the typical size of small molecules?

  About 10^-10 m.
• What are the key features of the current model of the atom?

  • Positively charged nucleus
  • Negatively charged electrons
  • Nucleus contains protons and neutrons
  • Most mass is in the nucleus
  • Electrons in fixed orbits (energy levels)
• How has the understanding of atomic structure evolved over time?

  1. Solid sphere model (early theory)
  2. Thomson's "plum pudding" model (1897)
  3. Rutherford's nuclear model (1909)
  4. Bohr's model with fixed electron orbits
  5. Current model with protons, neutrons, and electrons
• What is the significance of the nucleus in an atom?

  • Contains protons (positive charge)
  • Contains neutrons (neutral charge)
  • Holds most of the atom's mass
  • Tiny compared to the overall atom
• What are the implications of an atom gaining or losing electrons?

  • Losing an electron: becomes a positive ion (+ve)
  • Gaining an electron: becomes a negative ion (-ve)
  • Neutral atoms have equal protons and electrons