By postulating that electrons revolve in discrete orbits without radiating energy.
Explanation
The primary limitation of Rutherford’s nuclear model was its inability to explain the stability of the atom. According to classical electromagnetic theory (Maxwell’s theory), a charged particle in accelerated motion, such as an electron revolving in a circular orbit, should continuously radiate energy. This energy loss would cause the electron to spiral inward and eventually fall into the nucleus, rendering the atom unstable. Niels Bohr applied quantum theory to address this flaw.Option Analysis:
- By proposing that the nucleus is negatively charged. is Incorrect: Both Rutherford and Bohr agreed that the nucleus is positively charged. The stability issue was related to the electron's motion, not the charge of the nucleus.
- By suggesting that electrons are stationary. is Incorrect: Bohr did not propose that electrons are stationary. He maintained that electrons revolve around the nucleus but restricted their motion to specific paths.
- By postulating that electrons revolve in discrete orbits without radiating energy. is Correct: Bohr postulated that electrons revolve in specific, discrete orbits (also known as stationary states or energy levels) without radiating energy. He suggested that angular momentum is quantized, and as long as an electron remains in one of these allowed orbits, it does not lose energy, thereby ensuring the stability of the atom.
- By discovering the neutron to add mass to the nucleus. is Incorrect: The neutron was discovered by James Chadwick in 1932, long after Bohr proposed his model (1913). While neutrons contribute to nuclear mass and stability, their discovery was not the theoretical improvement Bohr used to explain why electrons do not collapse into the nucleus.
Key Takeaway: Bohr’s model overcame the instability problem of Rutherford’s model by introducing the concept of quantized, non-radiating orbits, where electrons can revolve without losing energy.