| Feature | Bohr Model | Quantum Mechanical Model |
|---|---|---|
| Electron trajectory | Fixed circular orbits | No definite trajectory (probability clouds) |
| Position | Precisely known (orbit radius r_n) | Described by probability density ψ^{2} |
| Basis | Postulates + classical mechanics | Schrödinger wave equation |
| Energy (H atom) | E_n = −13.6/ eV ✓ | Same formula (exact for H) |
| Works for | Hydrogen and hydrogen-like ions only | All atoms |
| Handles multi-electron | No (ignores e-e repulsion) | Yes (approximations available) |
| Angular momentum | L = nh/2π (always quantized, never zero) | L = √[l(l+1)]ℏ (can be zero for s orbitals!) |
| Explains Zeeman effect? | Partially (normal) | Yes (fully) |
| Inconsistency | Violates Heisenberg principle | Fully consistent |
| Orbital concept | Orbits (defined paths) | Orbitals (probability regions) |
| Magnetic properties | Cannot explain | Explained by spin and orbital quantum numbers |
Key Insight: Bohr's energy formula E_n = −13.6/ is still used for NEET calculations in hydrogen-like atoms, even though the orbital model replaces fixed orbits with probability distributions.