Question

Write down the postulates of Bohr atom model.

Answer 1

1. The electron in an atom moves around the nucleus in circular orbits under the influence of Coulomb electrostatic force of attraction. This Coulomb force gives the necessary centripetal force for the electron to undergo circular motion.
2. Electrons in an atom revolve around the nucleus only in certain discrete orbits called stationary orbits where it does not radiate electromagnetic energy. Only those discrete orbits allowed are stable orbits.
3. The angular momentum of the electrons in these stationary orbits are quantized that is, it can be written as integer or an integral multiple of `"h"/"2h"` called as reduced Planck’s constant – that is, h (read it as h-bar) and the integer n is called as principal quantum number of the orbit.
   l = nh;
   L = `"nh"/(2π)`;
   mvr = `"nh"/(2π)` where h = `"h"/(2π)`
   This condition is known as the angular momentum quantization condition.
4. An electron can jump from one orbit to another orbit by absorbing or emitting a photon whose energy is equal to the difference in energy (∆E) between the two orbital levels.
   energy quantization condition
   ∆E = `"E"_"final" – "E"_"initial" = hν = "hc"/lambda`
   

   λ – Wavelength or radiation
   C – Speed of light
   ν – Frequency of the radiation