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Write the postulates of Bohr’s Model. What are the demerits of the Bohr’s Model?

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Bohr’s Atomic:

Bohr (1913) gave an atomic model based on the study of Plank’s quantum theory and Radiation which over come, the short comings of Rutherfords atomic model and explains the general characters of structure and spectrum of hydrogen atom. Indeed, following two points were important for development of this model

(a) Dual nature of electro magnetic radiation

(b) Experimental observations of atomic spectrum indicate the electrons are quantized in atom

Neils Bohr (1913) was the first to explain quantitatively the general features of hydrogen atom structure and its spectrum. On the basis of Planck’s quantum theory, Bohr’s gave following assumptions.
1. In hydrogen atom electron revolves around nucleus in closed circular orbit.
2. There are various closed circular orbits around the nucleus that revolves only such orbits in which the angular momentum of electron is
integral multiple of \(\frac{h}{2 \pi}\)
\(m v r=\frac{n h}{2 \pi}\)
3. Each circular orbit possess a certain energy level, so there orbits are also known as energy level. Since in these orbits energy of revolving electron in constant so these are also known as stationary orbits. These orbits are denoted by K L M N or 1, 2,3,4.
4. The energy of orbit does not change with time but when an electron jumps to high or low level then it absorbs or emits the necessary amount of energy. This energy change is not continuous
5. During the transmission between two states absorbed or emitted radiation is given by following expression.

Where E2 and E1 are higher and lower energy states. This equation is known as law of Bohr’s frequency.
6. For revolving electron centrifugal force is equal to centripetal force.

Where Z = Atomic number, m = mass of electron
v = Velocity of electron, e- charge of electron
r = distance of electron from nucleus (atomic radius)

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