Niels Bohr was the first to propose a theoretical model of the atom using quantum theory, which is now known as the Bohr model. This model helped explain the structure of the hydrogen atom and the behavior of electrons in atoms.

Introduction:
The first use of quantum theory to explain the structure of the atom was made by Niels Bohr. This breakthrough in atomic theory laid the foundation for our understanding of the behavior of electrons and the structure of atoms.
Explanation:
Here is a detailed explanation of how Niels Bohr used quantum theory to explain the structure of the atom:
1. Background:
- Prior to Bohr's work, the prevailing model of the atom was the Thomson model, which depicted the atom as a positively charged sphere with electrons scattered throughout.
- However, this model failed to explain certain experimental observations, such as the stability of atoms and the discrete nature of atomic spectra.
2. Quantum Theory:
- Quantum theory, developed by Max Planck and others, proposed that energy is quantized and exists in discrete packets called quanta.
- Bohr applied this concept of quantization to the behavior of electrons in atoms.
3. Bohr's Model:
- Bohr proposed a new model of the atom, known as the Bohr model or the planetary model.
- According to this model, electrons orbit the nucleus in specific energy levels or shells.
- The energy levels are quantized, meaning that electrons can only occupy certain energy states.
- When an electron jumps from one energy level to another, it either absorbs or emits energy in discrete packets, corresponding to the difference in energy between the levels.
4. Balmer Series:
- One of the key successes of Bohr's model was its ability to explain the observed spectral lines of hydrogen.
- Bohr derived an equation, known as the Balmer formula, which accurately predicted the wavelengths of the spectral lines.
- This formula was based on the quantization of energy levels in the hydrogen atom.
5. Contributions and Impact:
- Bohr's model of the atom revolutionized our understanding of atomic structure and paved the way for further developments in quantum mechanics.
- His work earned him the Nobel Prize in Physics in 1922.
- Bohr's ideas laid the foundation for subsequent theories, such as quantum mechanics and quantum electrodynamics, which continue to be widely used in modern physics.
Conclusion:
Niels Bohr was the first to use quantum theory to explain the structure of the atom. His model, which incorporated the concept of quantized energy levels, provided a comprehensive explanation for the behavior of electrons in atoms. Bohr's contributions to atomic theory have had a lasting impact on the field of physics.

Niels Bohr.