Niels Bohr's atomic model establishes that electrons occupy discrete energy shells defined by specific quantum numbers (n=1,2,3...) rather than continuous orbits within the domain of quantum physics. The core principle dictates that radiation emission or absorption occurs exclusively during transitions between these fixed levels, where the radiated frequency is proportional to the exact energy difference ($\Delta E = h\nu$) involved in the jump from a higher state $E_2$ to a lower state $E_1$. This theoretical framework bridges classical mechanics and quantum theory by introducing quantized angular momentum as a fundamental constraint on electron stability.
Prerequisite chain context: requires Energy Levels and Sublevels in Atoms.