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Chemistry Question 52 – JEE-MAIN 2025

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Which of the following postulate of Bohr's model of hydrogen atom is not in agreement with quantum mechanical model of an atom?

Consider the core principles and descriptions of electron behavior in Bohr's model versus the quantum mechanical model.

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Ninja Strategy•Fundamental Difference in Electron Description

The most significant conceptual difference between Bohr's model and quantum mechanics is how they describe the electron's 'path' or 'location' within the atom.

Step 1: Review Bohr's Postulates✦ Active

Bohr's model of the hydrogen atom is based on several postulates:

1. Electrons revolve around the nucleus in fixed circular orbits (stationary states) without radiating energy.

2. Electrons can only exist in specific, quantized energy levels.

3. Energy is emitted or absorbed (as photons) when an electron transitions between these stationary states.

Step 2: Understand the Quantum Mechanical Model○ Expand

The quantum mechanical model describes electrons using wave functions and probability distributions (orbitals), not definite classical orbits. It also predicts quantized energy levels and photon emission/absorption during transitions, but fundamentally differs in the description of electron motion and location due to the Heisenberg Uncertainty Principle.

Step 3: Identify the Disagreement○ Expand

Comparing Bohr's postulates with the quantum mechanical model:

- Quantized energy levels (Option 1) and non-radiation in stationary states (Option 2) are consistent with quantum mechanics.

- Photon emission during transitions (Option 3) is also consistent.

- However, the postulate that electrons move in definite circular orbits (Option 4) is a classical concept and is directly contradicted by the quantum mechanical model, which describes electrons in terms of probability clouds (orbitals) rather than fixed paths.

💡 Teacher's Secret Hint

The key difference lies in the nature of electron 'motion' or 'location' within the atom.

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