Atomic Structure: Bohr Model, Quantum Numbers & Electronic Configuration
Study atomic models, Bohr theory, quantum mechanical model, quantum numbers, electronic configuration and principles for JEE Main Chemistry.
The central idea of this chapter
Atoms consist of nucleus and electrons in quantized energy states. This chapter connects classical and quantum models with electronic arrangement and periodic properties.
What should you understand first?
Atomic Structure is fundamental for entire Chemistry. Master Bohr model, quantum numbers and electronic configuration rules. This chapter links with periodic table and chemical bonding.
Core concepts
- Bohr model Eₙ = −13.6Z²/n² eV
- Quantum numbers n, l, m, s
- De Broglie λ = h/mv
- Heisenberg ΔxΔp ≥ h/4π
- Electronic config Aufbau, Pauli, Hund
Useful building blocks
- Orbit radius rₙ = 0.529n²/Z Å
- Velocity v = 2.18×¹⁰Z/n m/s
- Angular momentum mvr = nh/2π
- Orbital shape l = 0,1,2,3
- Electron capacity 2n² electrons
Atomic Structure formula sheet
Use consistent units. Apply Bohr formulas for hydrogen-like species (H, He+, Li2+) with proper atomic number Z.
| Topic | Formula / Relation | Meaning or use |
|---|---|---|
| Bohr radius | rn = 0.529 n2/Z Å | Radius of nth orbit |
| Bohr energy | En = −13.6 Z2/n2 eV | Energy of electron in nth orbit |
| Electron velocity | v = 2.18×¹⁰ Z/n m/s | Velocity in nth orbit |
| Angular momentum | mvr = nh/2π | Quantization condition |
| De Broglie wavelength | λ = h/mv = h/p | Wave nature of electron |
| Heisenberg uncertainty | Δx × Δp ≥ h/4π | Position-momentum uncertainty |
| Principal quantum no | n = 1, 2, 3... | Shell number, size, energy |
| Azimuthal quantum no | l = 0 to (n−1) | Subshell, shape (s,p,d,f) |
| Magnetic quantum no | m = −l to +l | Orbital orientation |
| Spin quantum no | s = +1/2 or −1/2 | Electron spin direction |
| Number of orbitals | n² | Total orbitals in nth shell |
| Max electrons | 2n2 electrons | Maximum electrons in nth shell |
| Aufbau principle | (n+l) rule | Order of filling orbitals |
| Hund's rule | Maximize unpaired spins | Degenerate orbitals filling |
How to approach Atomic Structure problems
First identify topic (Bohr, quantum numbers, configuration), then apply appropriate formula. Use quantum number rules systematically for electron arrangement.
Bohr model & dual nature
- Energy of orbit? Eₙ = −13.6Z²/n² eV
- Radius? rₙ = 0.529n²/Z Å
- Transition energy? ΔE = Ef − Ei
- De Broglie? λ = h/mv
- Uncertainty? ΔxΔp ≥ h/4π
Quantum numbers & configuration
- Valid quantum nos? Check rules
- Orbital from l? 0=s,1=p,2=d,3=f
- Filling order? (n+l) rule
- Electronic config? 1s 2s 2p...
- Unpaired electrons? Hund's rule
How to prepare Atomic Structure
Start with atomic models and Bohr theory, then master quantum numbers and their rules. Finish with electronic configuration and principles (Aufbau, Pauli, Hund).
What to do
- Learn Bohr model formulas for hydrogen-like species
- Understand de Broglie and Heisenberg concepts
- Master all four quantum numbers and their ranges
- Practise electronic configuration writing
- Revise Aufbau, Pauli and Hund's rules
Common mistakes
- Wrong sign in Bohr energy formula (negative)
- Confusing quantum number rules and ranges
- Wrong orbital filling order (remember (n+l) rule)
- Forgetting exceptions (Cr, Cu, etc.)
- Mixing up azimuthal and magnetic quantum numbers
Ready to test Atomic Structure?
Revise the formula sheet, then solve mixed JEE Main problems on Bohr model, quantum numbers and electronic configuration.
Atomic Structure FAQ
Short answers to frequently tested ideas in this chapter.
Quantum numbers describe electron's position and energy. Four quantum numbers are n (principal), l (azimuthal), m (magnetic) and s (spin).
Bohr model describes electrons in fixed circular orbits around nucleus. Energy En = −13.6Z2/n2 eV for hydrogen-like atoms.
Electronic configuration shows distribution of electrons in orbitals. It follows Aufbau principle, Pauli exclusion and Hund's rule.