Electronic structure

• What is the significance of electrons occupying 'shells' around the nucleus?


  It is fundamental to the whole of chemistry.
• What do electron shells represent in an atom?


  They are energy levels where electrons are found.
• What are the rules for electron shells?


  1. Electrons always occupy shells (energy levels).
  2. Lowest energy levels fill first (closest to nucleus).
  3. Maximum electrons per shell:

  • 1st shell: 2
  • 2nd shell: 8
  • 3rd shell: 8

  1. Atoms prefer full electron shells (like noble gases).
  2. Atoms with unfilled outer shells tend to react.
• How many electrons can the first shell hold?


  2 electrons
• How many electrons can the second shell hold?


  8 electrons
• How many electrons can the third shell hold?


  8 electrons
• Why are atoms happier when they have full electron shells?


  Full electron shells provide stability to the atom.
• What happens to most atoms regarding their outer shell?


  Most atoms have an unfilled outer shell, making them reactive.
• How can electron configurations be represented?


  • As diagrams
  • As numbers (e.g., 2, 8, 1)
• What is the electron configuration for sodium?


  2, 8, 1