State the postulates of Bhore modal atom?

Answer 1

Bohr gives a satisfactory explanation for the ability of an electron to orbit a nucleus without collapsing by giving 2 important postulates.
1. an electron can only revolve round a nucleus without lossing energy in certain allowed orbits only.
This is only possible when the angular momentum of the electron is quantised, that is L= nh / [2(22/7)], n= 1, 2, 3...
where L is angular momentum, n is no. of orbit, h is Planck's constant.

2. electromagnetic photon energy is radiated when an electron makes a transition from a higher energy level to a lower one and the frequency of the electromagnetic wave radiated is given by dE/h, where dE is difference in energy level.

Answer 2

The Bohr model, named after Niels Bohr, pictures atoms as a nucleus of neutrons and protons clumped together surrounded by electrons which orbit the nucleus like the planets in our solar system orbit the sun. Usually the pictures you see of this exaggerate the size of the nucleus compared to the electron orbits; in reality the nucleus is only about 1/10,000 the size of the atom, although it does contain nearly all of its mass.

The Bohr model turned out to be incorrect in its depiction of electron 'orbits': electrons actually exist in 'probability clouds' of various shapes hovering around the nucleus, and the nucleus itself does not have an absolutely precise location - both of these being a consequence of the Uncertainty Principle of quantum mechanics.

PS: Sorry, I was describing the planetary model, which preceded Bohr's. Bohr did figure out that electrons had to be restricted to certain shells or energy levels, but his model only worked for hydrogen, the simplest atom.