Introduction to Electron Configuration

• Objective: Understand how to write the electron configuration of elements and ions.

Key Concepts

• Electron Configuration: Representation of the distribution of electrons in atomic orbitals.
• Energy Levels and Sublevels:
  • 1st level: 1s
  • 2nd level: 2s, 2p
  • 3rd level: 3s, 3p, 3d
  • 4th level (optional for certain elements): 4s, 4p, 4d, 4f
• Capacity of Sublevels:
  • s: 2 electrons
  • p: 6 electrons
  • d: 10 electrons
  • f: 14 electrons

Writing Electron Configuration

Nitrogen

• Atomic Number: 7 (7 electrons)
• Electron Configuration:
  • 1s² 2s² 2p³
  • Total: 7 electrons

Aluminum

• Atomic Number: 13 (13 electrons)
• Electron Configuration:
  • 1s² 2s² 2p⁶ 3s² 3p¹
  • Total: 13 electrons

Iron (Fe²⁺ Ion)

• Atomic Number: 26 (Parent Atom), 24 (Fe²⁺)
• Steps:
  1. Write configuration for Fe (26 electrons):
     • 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
  2. Adjust for Fe²⁺ (remove 2 electrons from highest energy level 4s):
     • 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶
• Note: For transition metals, write parent atom configuration first.

Chloride Ion (Cl⁻)

• Atomic Number: 17 (Cl), 18 (Cl⁻)
• Electron Configuration of Cl⁻:
  • 1s² 2s² 2p⁶ 3s² 3p⁶
  • Total: 18 electrons

General Rules for Writing Electron Configurations

• Atoms: Match electron count to the atomic number.
• Ions:
  • Positively charged ions (cations): subtract electrons equal to charge.
  • Negatively charged ions (anions): add electrons equal to charge.
• Transition Metals: Write configuration of the atom first, then adjust for ion.
• Non-Transition Metals: Can directly write configuration based on ion's electron count.

Important Notes

• For transition metals, adjust electron configuration after writing the parent atom's configuration to account for charge.
• For non-transition metals, you can either write the atom's configuration first or directly write for the ion by adjusting the electron count.