In this class, we continue our exploration of Atomic Structure, one of the most fundamental chapters in Chemistry for the NDA & CDS 1 2026 examination. Understanding the structure of atoms helps build the foundation for chemical bonding, periodicity, and overall problem-solving in Chemistry.
This session (Class-3) focuses on refining your understanding of quantum numbers, orbitals, wave mechanics, and electronic configuration—topics that are frequently tested in NDA and CDS exams.
Subtopics Covered
1. Quantum Mechanical Model (Recap + Advanced Points)
- Limitations of Bohr’s model
- Introduction to Schrödinger wave equation
- Concept of wave functions (ψ) and probability distribution
- Significance of ψ and ψ²
2. Quantum Numbers (In-Depth Discussion)
- Principal quantum number (n)
- Azimuthal quantum number (l)
- Magnetic quantum number (mₗ)
- Spin quantum number (mₛ)
- Rules for valid quantum number combinations
3. Shapes of Orbitals
- Representation of s, p, and d orbitals
- Nodal planes and radial nodes
- Importance of shapes in chemical bonding
4. Electronic Configuration
- Aufbau principle
- Pauli’s exclusion principle
- Hund’s rule of maximum multiplicity
- Writing electronic configurations for elements
- Exceptions to electronic configuration (Cr, Cu, etc.)
5. Degeneracy & Energy Levels
- Degenerate orbitals
- Variation of energy with increasing n and l
- Role of shielding and penetration effect
6. Important Short Tricks for NDA/CDS
- Quick rules for identifying last electron
- Fast methods to find quantum numbers
- How to eliminate options using configuration logic
Conclusion
This class strengthens the conceptual understanding of quantum mechanics and the arrangement of electrons in atoms. Mastering these topics will enhance your accuracy and speed in NDA CDS Chemistry questions. A clear grasp of quantum numbers, orbitals, and electronic configurations is essential not just for exam performance but also for future topics like periodic classification and chemical bonding.
