Short Answer

Bohr’s atomic model was proposed by Niels Bohr in 1913 to explain the stability of atoms and the behavior of electrons. According to this model, electrons move in fixed circular orbits around the nucleus without losing energy. Each orbit has a specific energy level, and electrons can jump between levels by absorbing or emitting energy.

The model explained the spectral lines of hydrogen and introduced the concept of quantized energy levels. Bohr’s postulates helped refine Rutherford’s nuclear model and became the foundation for modern atomic theory and quantum mechanics.

Detailed Explanation :

Main Postulates of Bohr’s Model

Bohr refined Rutherford’s nuclear model to explain how electrons can orbit the nucleus without falling into it, solving the problem of atomic stability. His model introduced several key postulates:

1. Electrons Move in Fixed Orbits

Bohr proposed that electrons move in circular paths called orbits or shells around the positively charged nucleus. While moving in these orbits, electrons do not emit energy, which prevents them from spiraling into the nucleus, a limitation in Rutherford’s model.

2. Quantized Energy Levels

Each orbit corresponds to a specific energy level, meaning electrons can only occupy certain discrete energy levels. These quantized levels are numbered as n = 1, 2, 3…, with n = 1 being the closest to the nucleus. Electrons cannot exist between these levels.

3. Energy Absorption and Emission

Electrons can jump from one energy level to another by absorbing or emitting a specific amount of energy called a quantum of energy. When an electron moves to a higher level, it absorbs energy; when it falls to a lower level, it emits energy as light or radiation. This explained the spectral lines of hydrogen.

4. Stability of Orbits

The orbits where electrons move are stable and do not radiate energy. This solved the problem in Rutherford’s model, where electrons moving around the nucleus should continuously lose energy and collapse into the nucleus. Bohr showed that only certain orbits are allowed, ensuring atomic stability.

5. Relation of Energy and Orbit

Bohr derived a mathematical relationship between the energy of an electron and its orbit. The energy of an electron in a particular orbit is proportional to 1/n². This formula could accurately calculate the energy levels in hydrogen atoms and predict the wavelengths of spectral lines.

6. Spectral Lines Explained

Bohr’s model explained why hydrogen produces discrete spectral lines. Each line corresponds to a transition of electrons between specific energy levels. For example, the Balmer series in the visible spectrum is explained by electrons falling to the n = 2 energy level from higher levels.

Significance of Bohr’s Model

Bohr’s model was revolutionary for several reasons:

1. Explained hydrogen spectra: It successfully predicted the wavelengths of hydrogen’s emission lines.
2. Introduced quantum concepts: The idea of quantized energy levels laid the groundwork for quantum mechanics.
3. Refined atomic structure: It improved Rutherford’s nuclear model by explaining electron stability.
4. Basis for modern chemistry: The model helped explain chemical behavior, bonding, and periodic properties.

Limitations

Despite its success, Bohr’s model had limitations:

• It could not explain spectra of multi-electron atoms.
• It could not account for electron-electron interactions or fine spectral details.
• It was later replaced by the quantum mechanical model, which describes electrons as probability clouds rather than fixed orbits.

Even with these limitations, Bohr’s postulates were a critical step in understanding atomic structure and paved the way for modern atomic theory.

Conclusion

Bohr’s atomic model proposed that electrons move in fixed orbits with specific energy levels around the nucleus. Electrons absorb or emit energy when they jump between levels, explaining atomic stability and spectral lines. Bohr’s postulates refined Rutherford’s model, introduced the concept of quantization, and formed the foundation of modern atomic theory and quantum mechanics.