Introduction to Electron Configuration

Overview

• The lecture provides a simple introduction on how to write the electron configuration of elements.

Key Concepts

• Periodic Table Information:

  • Nitrogen: Atomic Number = 7, Mass Number = 14.
  • Higher number = Mass Number; lower number = Atomic Number.

• Energy Levels and Sublevels:

  • 1st Energy Level: 1s
  • 2nd Energy Level: 2s, 2p
  • 3rd Energy Level: 3s, 3p, 3d
  • 4th Energy Level: 4s, 4p, 4d, 4f

Electron Capacity of Sublevels

• s sublevel can hold 2 electrons.
• p sublevel can hold 6 electrons.
• d sublevel can hold 10 electrons.
• f sublevel can hold 14 electrons.

Writing Electron Configuration for Nitrogen

• Total number of electrons in Nitrogen = 7.
• Configuration Steps:
  1. Start with 1s: 1s²
  2. Move to 2s: 2s²
  3. Move to 2p: 2p³ (3 electrons needed)
• Final Configuration for Nitrogen: 1s² 2s² 2p³

Writing Electron Configuration for Aluminum

• Total number of electrons in Aluminum = 13.
• Configuration Steps:
  1. 1s²
  2. 2s²
  3. 2p⁶
  4. 3s²
  5. Move to 3p: 3p¹
• Final Configuration for Aluminum: 1s² 2s² 2p⁶ 3s² 3p¹

Writing Electron Configuration for Ions

Example: Iron (Fe²⁺)

• Atomic Number of Fe = 26 (26 electrons).
• Fe²⁺ has lost 2 electrons => Total = 24 electrons.
• Configuration Steps:
  1. 1s²
  2. 2s²
  3. 2p⁶
  4. 3s²
  5. 3p⁶
  6. 4s²
  7. Move to 3d: 3d⁶ (only need 6 more electrons)
• Final Configuration for Fe²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶

Important Note on Transition Metals

• For transition metals, write the parent atom's configuration first, and then remove electrons corresponding to the charge from the highest energy level.

Writing Electron Configuration for Chlorine Ion (Cl⁻)

• Atomic Number of Cl = 17.
• Cl⁻ has gained an electron => Total = 18 electrons.
• Configuration Steps:
  1. 1s²
  2. 2s²
  3. 2p⁶
  4. 3s²
  5. 3p⁶ (6 more electrons needed)
• Final Configuration for Cl⁻: 1s² 2s² 2p⁶ 3s² 3p⁶

Summary of Key Rules

• For transition metals, first write the configuration for the neutral atom, then adjust for ions (subtract electrons for positive ions).
• For non-transition metals, directly write the configuration for the ion by counting total electrons, adding for negative ions and subtracting for positive ions.