Lecture Notes: Atomic and Molecular Structure

Introduction

• Topic: Atomic and Molecular Structure
• Focus: Unit 1 of the syllabus
• Breakdown: Covered in Part 1 and Part 2

Topics Covered

• Molecular Orbital Diagram of N2 and O2
• Bond Order and Magnetic Behavior

Exam Format

• Example Question: Draw the molecular orbital diagram of N2, determine its bond order, and discuss its magnetic behavior based on molecular orbital theory.

Key Concepts

N2 Molecular Orbital Formation

• Atomic Configuration: N has an atomic number of 7, configuration 1s² 2s² 2p³.
• Molecular Formation: N2 molecule forms when two nitrogen atoms combine.
• Energy Levels:
  • 1s < 2s < 2p (increasing energy levels)
• Bonding and Antibonding Orbitals:
  • Bonding (σ) and Antibonding (σ*) formed from overlapping atomic orbitals.

Bonding in Molecular Orbitals

• 1s Orbital: Always forms sigma bond.
• 2s Orbital: Forms sigma bond (σ) and antibonding orbital (σ*).
• 2p Orbitals: Three orbitals available; fill with single electrons first, then pair.
• Formation of Sigma (σ) and Pi (π) Bonds:
  • Sigma bonds formed by end-to-end overlap.
  • Pi bonds formed by side-by-side overlap.

Electron Filling and Magnetic Behavior

• Electron filling order:
  • Fill from the lowest energy level to the highest.
• Magnetic Behavior:
  • Diamagnetic: All electrons paired.
  • Paramagnetic: Presence of unpaired electrons.

Molecular Orbital Diagrams

1. N2 Diagram:

   • Bond Order Calculation:
     • Bonding electrons (σ, π) - Antibonding electrons (σ*, π*) = 10 - 4 = 6.
     • Bond Order = 6/2 = 3 (triple bond).
   • Magnetic Behavior: Diamagnetic (all electrons paired).

2. O2 Diagram:

   • Total electrons = 16.
   • Bond Order: 2 (double bond).
   • Magnetic Behavior: Paramagnetic (2 unpaired electrons).

3. CO Diagram:

   • Total electrons = 14.
   • Bond Order: 3 (triple bond).
   • Magnetic Behavior: Diamagnetic.

Conclusion

• Covered the formation of molecular orbitals and bonding theories.
• Next steps:
  • Continue with molecular theory postulates.
  • Practical application of molecular orbital diagrams.

Thank You!

• End of lecture.