Short Answer

The quantum mechanical model differs from Bohr’s model in how it describes the behavior and location of electrons. Bohr’s model assumes that electrons move in fixed circular orbits around the nucleus, with specific energy levels.

In contrast, the quantum mechanical model, based on Schrödinger’s equation, describes electrons as wave-like particles that exist in regions called orbitals, where they are most likely to be found. This model accounts for electron behavior more accurately, including multi-electron atoms and chemical bonding, which Bohr’s model could not explain.

Detailed Explanation :

Differences Between Quantum Mechanical Model and Bohr’s Model

Bohr’s atomic model, proposed in 1913, was an important step in explaining atomic structure. It introduced quantized energy levels, successfully explaining hydrogen’s spectral lines. However, Bohr’s model had limitations, such as its inability to explain multi-electron atoms, chemical bonding, and electron behavior beyond hydrogen. The quantum mechanical model emerged to address these limitations.

1. Electron Position and Motion

• Bohr’s Model: Electrons move in fixed circular orbits around the nucleus. The exact path and position of an electron at any time are assumed to be known.
• Quantum Mechanical Model: Electrons behave like both particles and waves. Their position cannot be pinpointed exactly. Instead, they exist in orbitals, which are regions around the nucleus where electrons are most likely to be found. This concept is derived from the Heisenberg Uncertainty Principle, which states that we cannot know both the position and momentum of an electron simultaneously.

2. Energy Levels and Orbits

• Bohr’s Model: Electrons can only occupy discrete circular orbits with fixed energy. Energy is absorbed or emitted when electrons jump between these levels.
• Quantum Mechanical Model: Electrons occupy energy sublevels within shells, and orbitals have different shapes (s, p, d, f). Energy levels are more complex, allowing a more accurate description of multi-electron atoms.

3. Explanation of Spectra

• Bohr’s Model: Works well for hydrogen’s simple spectral lines but fails for atoms with more than one electron.
• Quantum Mechanical Model: Explains the spectra of multi-electron atoms and the fine structure of spectral lines using electron wave functions.

4. Electron Behavior

• Bohr’s Model: Electrons move in predictable paths around the nucleus, and their motion is classical.
• Quantum Mechanical Model: Electrons behave as wave-particles, showing probabilistic behavior. Their exact path is unknown; only the probability of finding an electron in a region can be determined.

5. Chemical Bonding and Electron Configuration

• Bohr’s Model: Cannot explain chemical bonding in multi-electron atoms or molecules.
• Quantum Mechanical Model: Accurately describes electron configuration, bonding, and molecular geometry using orbitals and Pauli Exclusion Principle, which Bohr’s model does not.

6. Compatibility with Modern Physics

• Bohr’s Model: Partly compatible with classical physics but fails for complex systems and phenomena.
• Quantum Mechanical Model: Fully compatible with quantum mechanics, including Schrödinger’s wave mechanics and Heisenberg’s uncertainty principle. It explains atomic and molecular properties more accurately.

Significance of the Quantum Mechanical Model

The quantum mechanical model provides a complete and realistic picture of atoms:

1. Accounts for electron behavior in all atoms, not just hydrogen.
2. Explains the shapes of molecules and periodic properties.
3. Provides a foundation for modern chemistry and technologies like semiconductors, lasers, and quantum computing.
4. Corrects the limitations of Bohr’s model while retaining the concept of quantized energy levels.

Conclusion

The quantum mechanical model differs from Bohr’s model in that it describes electrons as wave-like particles in orbitals rather than moving in fixed circular paths. It explains multi-electron atoms, chemical bonding, and spectral lines accurately, overcoming Bohr’s model limitations. The quantum mechanical model is the foundation of modern atomic theory and provides a detailed and realistic description of atomic structure.