Electron Configuration Introduction

Basics of Electron Configuration

• Periodic Table Basics
  • Mass number: Higher of the two numbers.
  • Atomic number: Smaller integer.
• Energy Levels and Sublevels
  • 1st Energy Level: 1s sublevel.
  • 2nd Energy Level: s and p sublevels.
  • 3rd Energy Level: s, p, and d sublevels.

Writing Electron Configurations

• Sublevel Electron Capacity
  • s: Can hold 2 electrons.
  • p: Can hold 6 electrons.
  • d: Can hold 10 electrons.
  • f: Can hold 14 electrons.
• General Process
  • Start from 1s and work upwards.
  • Add electrons to sublevels according to their maximum capacity.
  • Stop when the total number of electrons equals the atomic number or adjusted for ions.

Example: Nitrogen

• Atomic Details
  • Atomic number: 7.
  • Electrons: 7.
• Configuration Steps
  • 1s: 1s².
  • 2s: 2s².
  • 2p: 2p³.
• Resulting Configuration: 1s² 2s² 2p³.

Example: Aluminum

• Atomic Details
  • Atomic number: 13.
  • Electrons: 13.
• Configuration Steps
  • 1s: 1s².
  • 2s: 2s².
  • 2p: 2p⁶.
  • 3s: 3s².
  • 3p: 3p¹.
• Resulting Configuration: 1s² 2s² 2p⁶ 3s² 3p¹.

Ions and Electron Configuration

• Iron (Fe) Example
  • Atomic number: 26.
  • Fe²⁺: 24 electrons (2 electrons lost).
  • Write configuration for neutral atom first.
  • Remove electrons starting from the highest energy level.
  • Neutral Fe Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶.
  • Fe²⁺ Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ (remove 4s²).

Non-Transition Metal Ions

• Chloride Ion (Cl⁻) Example
  • Chlorine atomic number: 17.
  • Chloride: 18 electrons (1 extra electron).
  • Configuration based on total electrons in ion.
  • Cl⁻ Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶.

Tips for Electron Configurations

• Transition Metals: Write neutral atom configuration first, adjust by removing electrons for positive ions.
• Non-Transition Elements: Directly write configuration based on ion electron count.
• Electron Additions/Subtractions
  • Positive ions: Subtract electrons.
  • Negative ions: Add electrons.
• Energy Level Order: Remove from the highest energy level first when adjusting for ions.