Electron Configuration Introduction

Overview

• Explanation of how to write the electron configuration of elements.
• Focus on nitrogen and aluminum as examples, and ions such as Fe²⁺ and Cl⁻.

Key Concepts

Periodic Table Information

• Atomic Number: the smaller number, represents the number of protons (also electrons in neutral atoms).
• Mass Number: the larger number, represents the total number of protons and neutrons.

Energy Levels and Sublevels

• First Energy Level: 1s
• Second Energy Level: 2s and 2p
• Third Energy Level: 3s, 3p, and 3d
• Fourth Energy Level: 4s, 4p, 4d, and 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

Example 1: Nitrogen (N)

• Atomic Number: 7 (7 protons and 7 electrons)
• Electron Configuration:
  • 1s² (2 electrons)
  • 2s² (2 electrons)
  • 2p³ (3 electrons)
  • Final Configuration: 1s² 2s² 2p³

Example 2: Aluminum (Al)

• Atomic Number: 13 (13 electrons)
• Electron Configuration:
  • 1s² (2 electrons)
  • 2s² (2 electrons)
  • 2p⁶ (6 electrons)
  • 3s² (2 electrons)
  • 3p¹ (1 electron)
  • Final Configuration: 1s² 2s² 2p⁶ 3s² 3p¹

Electron Configuration for Ions

Example 3: Iron Ion (Fe²⁺)

• Atomic Number of Fe: 26 (26 electrons in neutral atom)
• Fe²⁺: loses 2 electrons, so has 24 electrons.
• Configuration for Fe:
  • 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
• Remove 2 electrons from highest energy level (4s):
  • Final Configuration for Fe²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶

Example 4: Chloride Ion (Cl⁻)

• Atomic Number of Cl: 17 (17 electrons in neutral atom)
• Configuration for Cl:
  • 1s² 2s² 2p⁶ 3s² 3p⁵
• Chloride Ion (Cl⁻): Gains 1 electron (total 18 electrons)
• Final Configuration for Cl⁻: 1s² 2s² 2p⁶ 3s² 3p⁶

Summary

• For transition metals, write the configuration of the parent atom first and then adjust for the ion.
• For non-transition metals, you can directly write the configuration for the ion based on the total number of electrons.