Lecture Notes on Electron Configuration and Orbital Diagrams

Introduction

• Focus on electron configuration and writing orbital diagrams for elements.
• Example elements: Sulfur, Nitrogen, Aluminum, Cobalt, Chromium, and Copper.

Sulfur

• Atomic Details:
  • Atomic number: 16 (protons = electrons).
  • Mass number: 32.
• Electron Configuration:
  • Ground state: 1s² 2s² 2p⁶ 3s² 3p⁴.
• Orbital Diagrams:
  • Boxes represent orbitals with electrons shown as arrows with opposite spins.
  • Hund’s Rule: add electrons with parallel spins before pairing.
• Noble Gas Notation:
  • Ne [Ne] 3s² 3p⁴.
• Sulfide Ion Configuration:
  • S²⁻ ion with 18 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶.

Nitrogen

• Atomic Details:
  • Atomic number: 7.
• Electron Configuration:
  • Ground state: 1s² 2s² 2p³.
• Noble Gas Notation:
  • He [He] 2s² 2p³.
• Nitride Ion Configuration:
  • N³⁻ ion with 10 electrons: 1s² 2s² 2p⁶.
• Magnetic Properties:
  • Nitrogen: paramagnetic (unpaired electrons).
  • Nitride Ion: diamagnetic (paired electrons).

Aluminum

• Atomic Details:
  • Atomic number: 13.
• Electron Configuration:
  • Ground state: 1s² 2s² 2p⁶ 3s² 3p¹.
• Noble Gas Notation:
  • Ne [Ne] 3s² 3p¹.
• Aluminum Ion Configuration:
  • Al³⁺ ion with 10 electrons: 1s² 2s² 2p⁶.
• Magnetic Properties:
  • Paramagnetic (one unpaired electron).

Cobalt

• Atomic Details:
  • Atomic number: 27.
• Electron Configuration:
  • Ground state: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷.
• Noble Gas Notation:
  • Ar [Ar] 4s² 3d⁷.
• Magnetic Properties:
  • Paramagnetic (3 unpaired electrons).
• Cobalt Ions:
  • Co²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷.
  • Co³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶.

Exceptions in Electron Configuration

• Chromium (Cr):
  • Atomic number: 24.
  • Configuration: [Ar] 4s¹ 3d⁵ (exception to expected 4s² 3d⁴).
• Copper (Cu):
  • Atomic number: 29.
  • Configuration: [Ar] 4s¹ 3d¹⁰ (exception to expected 4s² 3d⁹).

Key Concepts

• Hund’s Rule: Electrons prefer separate orbitals at the same energy level before pairing.
• Paramagnetism and Diamagnetism:
  • Paramagnetic: Substances with unpaired electrons.
  • Diamagnetic: Substances with all electrons paired.
• Valence Electrons: Electrons in the highest energy level; participate in chemical reactions.
• Core Electrons: Non-valence electrons; inner electrons.

Conclusion

• Understanding electron configuration helps in predicting chemical properties and reactivity.
• Knowing exceptions in electron configurations is crucial for transition metals.

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These notes cover electron configurations, orbital diagrams, and related concepts thoroughly, providing a solid foundation for understanding the electronic structure of atoms.