The Nuclear Model

• What led to the replacement of the Plum Pudding model?

  The results of the alpha scattering experiment
• What does the nuclear model state about the structure of an atom?

  Most of an atom is empty space with a positive nucleus and negative electrons
• Who proposed that electrons orbit the nucleus at specific distances?

  Neils Bohr
• What are the specific distances where electrons orbit the nucleus called?

  Energy levels or shells
• What are protons and what do they determine in an atom?

  Protons are positive particles that determine the positive charge in the nucleus
• How many protons does a hydrogen atom have?

  One proton
• How many protons does a helium atom have?

  Two protons
• What did James Chadwick discover about the nucleus?

  He discovered that the nucleus contains neutral particles called neutrons
• What is the approximate radius of an atom?

  0.1 nanometers or $1 \times 10^{-10} \text{ m}$
• What is the approximate radius of the nucleus?

  $1 \times 10^{-14} \text{ m}$
• Where is most of the mass of an atom found?

  In the nucleus
• What is the relative charge of protons?

  Positive one
• What is the relative charge of neutrons?

  Zero
• What is the relative charge of electrons?

  Negative one
• Why do atoms have no overall charge?

  Because the number of electrons equals the number of protons
• What is the relative mass of protons and neutrons?

  Both have a relative mass of one
• How does the relative mass of electrons compare to protons and neutrons?

  Electrons have a much smaller relative mass than protons and neutrons
• Do you need to know the exact relative mass of an electron for the exam?

  No, you only need to know it is very small
• What are the modifications made to the nuclear model of atomic structure?

  • Electrons orbit the nucleus at specific distances (energy levels or shells)
  • Protons were discovered as positive particles in the nucleus
  • Neutrons were discovered as neutral particles in the nucleus
• What are the relative charges and masses of protons, neutrons, and electrons?

  • Protons:
  • Relative charge: +1
  • Relative mass: 1
  • Neutrons:
  • Relative charge: 0
  • Relative mass: 1
  • Electrons:
  • Relative charge: -1
  • Relative mass: very small
• What is the significance of the number of protons in an atom?

  • Determines the positive charge of the nucleus
  • Defines the element (e.g., hydrogen has 1 proton, helium has 2 protons)