The Bohr Atomic model : Quantisation of matter
After the Einstein’s photon theory and James Clerk Maxwell’s electricity and light manifestations theory things was getting heated up to form the first model of the Atom.Basically the Atom is the smallest particle of a chemical element that can exist. Every solid, liquid, gas and ions on the universe are composed with Atom.
By the dawn of the 20th century the evidence required a model of the atom with a diffuse cloud of negatively charged electrons surrounding a small, dense, positively charged nucleus. All these properties suggested a model in which electrons circle around the nucleus. Imagine solar system, planets orbiting a sun. Where sun is nucleus and planets are electrons. But, According to the classical theory the atom in this model would be unstable. The orbiting electrons experience the centripetal acceleration, and should therefore give off electromagnetic radiation, and loss of energy which cause them to spiral toward the nucleus. So the Atom collide with it in a fraction of a second.
In 1931 Neil Bohr come up with his quantised model of atom often known as Bohr Atomic model. This model can explain how electron can have stable orbits around the nucleus. Earlier the Rutherford model which was unstable because the charged particle moving on a curved path emits electromagnetic radiation; thus, the electrons would lose energy and spiral into the nucleus. The Bohr modified this model by requiring that the electrons move in orbits of fixed size and energy.
As might expected in classical theory, when an atom emitted or absorbed energy, the electron did not move in a continuous trajectory from one orbit around the nucleus to another. But, the electron would jump instantaneously from one orbit to another, giving off the emitted light in the form of a photon. The radiation only occur when the electron jumps from one orbit to another. The atom will be completely stable in the state with the smallest orbit, since there is no orbit of lower energy into which the electron can jump.
So, just with one simple assumption, the Bohr Atomic model was able to relate the observed spectral lines in the emission spectrum of hydrogen to previously known constants. Well, the this model electrons simply wasn’t allowed to emit energy continuously and crash into the nucleus. Once the electron closest permitted orbit, it become stable forever.
However, the Bohr Atomic model didn’t explain why orbits should be quantised in that way, nor was it able to make accurate predictions for atoms with more than one electron, or to explain why some spectral lines are brighter than others.
The Bohr model can predict the emission spectrum of hydrogen in terms of fundamental constants. However, it was not able to make accurate predictions for multi-electron atoms, or to explain why some spectral lines are brighter than others. But later on some of the fundamental assumptions of model were found to be wrong.