Lecture on Electronic Structure of Atoms

Introduction

• Presenter: Iman
• Topic: Electronic structure of atoms, focusing on the quantum mechanical model.

Bohr's Model and Its Limitations

• Initially promising as it matched hydrogen emission spectrum data.
• Failed for atoms with more than one electron.
• Conclusion: Bohr's model is fundamentally incorrect for multi-electron atoms.

Development of Quantum Mechanics

• Advancement: Wave mechanical model by Schrödinger and Heisenberg.
• Key Difference: Bohr's electrons in circular orbits vs. quantum mechanics' probabilistic wave-like electron distribution.
• Orbitals vs. Orbits: Modern theory uses orbitals, regions determined by electron probability.

Quantum Mechanics Concepts

• Wave Equation: Describes electron behavior.
• Wave Functions: Solutions to wave equations that determine electron energy levels.
• Probability Density: Square of wave function gives probability of finding an electron.
• Heisenberg Uncertainty Principle: Impossible to know both momentum and position of an electron simultaneously.

Quantum Numbers

• Describe energy, shape, orientation, and electron spin in orbitals.

1. Principle Quantum Number (n): Energy level and size of orbitals. Higher n = larger, more energetic orbitals.
2. Angular Momentum Quantum Number (L): Shape of orbitals. Values range from 0 to n-1.
   • L=0: S subshell
   • L=1: P subshell
   • L=2: D subshell
   • L=3: F subshell
3. Magnetic Quantum Number (ML): Orientation of orbitals, values range from -L to +L.
4. Spin Quantum Number (MS): Spin orientation of electrons, values of +½ or -½.

Electron Configuration Principles

• Aufbau Principle: Fill lowest energy orbital first.
• Pauli Exclusion Principle: Max two electrons per orbital with opposite spins.
• Hund’s Rule: Fill degenerate orbitals singly before pairing.

Shells, Subshells, and Orbitals

• Shells: Primary energy levels (n).
• Subshells: Defined by L, shape of space for electrons.
• Orbitals: Regions in subshells where electrons are likely found.

Electron Configuration

• Method: Use periodic table layout to determine electron distribution.
• Notation: Spectroscopic notation indicates energy levels, subshells, and electron counts.

Exceptions in Electron Configurations

• Some transition metals (e.g., Chromium, Copper) deviate from expected electron configurations for stability.
  • Chromium: Prefers half-filled d subshell.
  • Copper: Prefers full d subshell.

Conclusion

• Quantum mechanics provides a comprehensive framework for understanding atomic structure.
• Questions and comments are encouraged for clarification and understanding.