According to Bohr’s model, where are electrons found in an atom?

Question

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The correct answer is Option A: Moving in fixed circular orbits around the nucleus. According to Bohr's atomic model, electrons revolve around the nucleus in discrete, stable, circular paths called stationary orbits or shells. These orbits have fixed energy levels, meaning an electron in a specific orbit possesses a constant amount of energy.

Step-by-Step Solution & Concepts:
According to Bohr's atomic model, electrons revolve around the nucleus in discrete, stable, circular paths called stationary orbits or shells. These orbits have fixed energy levels, meaning an electron in a specific orbit possesses a constant amount of energy.

Working Principle: Bohr postulated that electrons move in orbits where their angular momentum is quantized, defined by the condition $mvr = \frac{nh}{2\pi}$. Electrons do not radiate energy while moving in these stationary states, contrary to classical electromagnetic theory. Radiation occurs only when an electron jumps from a higher energy shell ($E_2$) to a lower one ($E_1$), emitting a photon with energy $\Delta E = E_2 - E_1 = h
u$.

Key Formulas: $L = mvr = \frac{nh}{2\pi}$ — Angular momentum quantization condition; $\Delta E = h
u$ — Energy of emitted or absorbed photon

Key Points: Electrons revolve only in orbits with specific, fixed energy levels.; The energy of an orbit is quantized, represented by the principal quantum number '$n$'.; No energy is lost or gained by an electron as long as it stays in its designated orbit.; Electrons emit or absorb radiation only during 'quantum jumps' between energy levels.

Advantages: Successfully explained the stability of the atom.; Provided a theoretical basis for the hydrogen line spectrum (Rydberg formula).

Disadvantages: Failed to explain the spectra of multi-electron atoms.; Could not explain the Zeeman effect or Stark effect.; Violates the Heisenberg Uncertainty Principle.

Applications: Foundation for quantum mechanics; Spectroscopy and analytical chemistry

Additional Info: The principal quantum number $n$ can take positive integer values 1, 2, 3... corresponding to K, L, M shells.. Option B is incorrect because the nucleus contains only protons and neutrons.. Option C is incorrect as it describes the modern electron cloud model, which replaced Bohr's fixed orbits.. Option D is incorrect as electrons are bound to the nucleus by electrostatic force.

Answer: A is correct — Bohr proposed that electrons move in fixed, non-radiating circular orbits around the nucleus, each associated with a specific energy level.

Exam Tip: In competitive exams, remember that Bohr's model is valid specifically for single-electron species like $H$, $He^+$, and $Li^{2+}$.

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Option B: Fixed positions inside the nucleus

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Option C: Randomly scattered inside the atom

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Option D: Resting outside the atom in free space

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