JEE Main 2025 · 3 April · morning · Single correct · +4 / −1
Which of the following postulate of Bohr's model of hydrogen atom is not in agreement with quantum mechanical model of an atom?
- (a) The electron in a H atom's stationary state moves in a circle around the nucleus.
- (b) An atom can take only certain distinct energies E₁, E₂, E₃, etc. These allowed states of constant energy are called the stationary states of atom.
- (c) An atom in a stationary state does not emit electromagnetic radiation as long as it stays in the same state.
- (d) When an electron makes a transition from a higher energy stationary state to a lower energy stationary state, then it emits a photon of light.
Answer and solution
Answer (a) The electron in a H atom's stationary state moves in a circle around the…
Solution
Chemistry ma’am · 3 steps
Bohr's quantised energies survive in quantum mechanics; his neat circular track for the electron does not.
- What QM keeps. The quantum mechanical model also gives an atom only certain allowed energies. An electron in such a state does not radiate, and it emits a photon of energy hν = E₂ - E₁ when it drops to a lower state.
- What QM rejects. A circular orbit means the electron has an exact position and an exact momentum at every instant. The Heisenberg uncertainty principle says both cannot be known together, so a definite path is not allowed.
Postulate Quantum mechanical model Agrees? (a) Electron moves in a circle Only a probability of finding the electron (orbital), no fixed path No (b) Only certain energies allowed Energies come out quantised from the Schrödinger equation Yes (c) No radiation in a stationary state A stationary state has constant energy, so nothing is emitted Yes (d) Photon emitted on going down Δ E = hν is released as light Yes - So. The postulate in conflict with quantum mechanics is the circular orbit, option (a).
The idea to keep. Quantum mechanics keeps the energy levels but gives up the idea of a path. Any statement about a definite orbit or trajectory of the electron is the Bohr idea that fails.
Answer from the NTA final answer key. Solution by PrepWiser.