Which scientist gave the concept of fixed energy levels around the nucleus ?

Question

Accepted Answer

The concept of fixed energy levels around the nucleus was introduced by Neils Bohr, making Option 2 the correct answer. Here is a detailed explanation supporting this choice:

1. **Explanation for Option 2 (Neils Bohr):**
   Neils Bohr, a Danish physicist, proposed the Bohr model of the atom in 1913. This model introduced the idea that electrons orbit the nucleus in specific, quantized energy levels or shells. According to Bohr's theory, electrons can only occupy certain allowed orbits with fixed energies, and they can move between these orbits by absorbing or emitting energy in the form of photons. This concept was revolutionary because it explained the stability of atoms and the emission spectra of hydrogen, providing a foundation for modern quantum mechanics.

2. **Explanation for why other options are incorrect:**

- **Option 1 (J. J. Thomson):**
     J. J. Thomson is best known for his discovery of the electron and his "plum pudding" model of the atom, which depicted the atom as a sphere of positive charge with electrons embedded within it. This model did not include the concept of fixed energy levels or orbits around the nucleus, making it fundamentally different from Bohr's model.

- **Option 3 (Ernest Rutherford):**
     Ernest Rutherford is credited with the discovery of the atomic nucleus through his gold foil experiment. He proposed the nuclear model of the atom, where a dense, positively charged nucleus is surrounded by electrons. However, Rutherford's model did not specify fixed energy levels for the electrons; it was Bohr who later refined this model by introducing quantized orbits.

- **Option 4 (William Crooks):**
     William Crooks was a chemist and physicist known for his work with cathode rays and the invention of the Crookes tube. His contributions were significant in the study of electrical discharge in gases, but he did not develop a model of the atom or propose the concept of fixed energy levels.

In conclusion, Neils Bohr's introduction of fixed energy levels was a pivotal advancement in atomic theory, distinguishing his work from that of other scientists mentioned in the options. This is why Option 2 is the correct answer.