In this postulate, Bohr incorporated early quantum concepts into the atomic theory. Hence, the angular momentum (L) of the orbiting electron is: L = nh/2p.The angular momentum of revolution is an integral multiple of h/2p – where hàPlanck’s constant.An electron revolves around the nucleus in orbits.Postulate IIīohr defined these stable orbits in his second postulate. Also, each state has a definite total energy. Further, he stated that each atom can exist in certain stable states. In a radical departure from the established principles of classical mechanics and electromagnetism, Bohr postulated that in an atom, electron/s could revolve in stable orbits without emitting radiant energy. Watch Modern Atomic Theory –īohr, in an attempt to understand the structure of an atom better, combined classical theory with the early quantum concepts and gave his theory in three postulates: Postulate I

However, actual observation tells us that the electron emits a line spectrum. In other words, it would emit a continuous spectrum. This would mean that, as the electron spirals inwards, it would emit electromagnetic waves of changing frequencies. The classical electromagnetic theory also states that the frequency of the electromagnetic waves emitted by an accelerating electron is equal to the frequency of revolution. Therefore, the energy of such an electron should constantly decrease and the electron should collapse into the nucleus. Also, an object moving in a circle undergoes constant acceleration due to the centripetal force.įurther, electromagnetic theory teaches us that an accelerating charged particle emits radiation in the form of electromagnetic waves. This is because the nucleus and electrons are charged particles.

However, the fundamental difference between the two is that, while the planetary system is held in place by the gravitational force, the nucleus-electron system interacts by Coulomb’s Law of Force. According to Rutherford’s model, an atom has a central nucleus and electron/s revolve around it like the sun-planet system. Bohr model of the hydrogen atom attempts to plug in certain gaps as suggested by Rutherford’s model by including ideas from the newly developing Quantum hypothesis.

Bohr's model of an atom