Rutherford's model of an atom, often referred to as the "planetary model," depicted electrons orbiting the nucleus in a manner similar to planets orbiting the Sun. According to classical electromagnetic theory, an accelerating charged particle, such as an electron moving in a circular orbit, should continuously radiate energy in the form of electromagnetic waves. This emission of energy would cause the electron to lose momentum and eventually spiral into the nucleus, resulting in the collapse of the atom. This phenomenon is known as the "classical electron collapse problem."
Bohr's model of the atom, proposed by Niels Bohr in 1913, addressed the stability issue of Rutherford's model by incorporating the principles of quantization and the newly emerging theory of quantum mechanics. Bohr introduced the idea that electrons could only occupy specific energy levels or orbits around the nucleus, and these orbits were quantized, meaning they had discrete energy values. Electrons were confined to these specific orbits without radiating energy, which prevented them from collapsing into the nucleus.
Bohr's model resolved the instability problem by suggesting that electrons could only transition between these quantized energy levels by absorbing or emitting energy in discrete amounts, known as quanta or photons. When an electron absorbs energy, it moves to a higher energy level or orbit. Conversely, when an electron emits energy, it transitions to a lower energy level or orbit. This emission and absorption of energy occur in fixed quantities, corresponding to the difference in energy between the orbits.
The stability of Bohr's model arises from the fact that electrons remain in their energy levels without losing energy as they orbit the nucleus. The model successfully explained the spectral lines observed in the emission and absorption spectra of atoms, providing a theoretical foundation for understanding atomic structure and the behavior of electrons within an atom.
However, it is important to note that Bohr's model is a simplified representation of atomic structure and has its limitations. It was later replaced by more accurate and comprehensive models, such as the quantum mechanical model, which describes the behavior of electrons using wave functions and probability distributions rather than definite orbits. Nonetheless, Bohr's model played a crucial role in the development of quantum theory and paved the way for further advancements in our understanding of atomic physics.