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Question
Write postulates of Bohr’s Theory of hydrogen atom.
Solution
Postulates of Bohr’s theory of hydrogen atom:
- The electron in the hydrogen atom can move around the nucleus in one of the many possible circular paths of fixed radius and energy. These paths are called orbits, stationary states, or allowed energy states. These orbits are arranged concentrically around the nucleus in increasing order of energy.
- The energy of an electron in the orbit does not change with time. However, the electron will move from a lower stationary state to a higher stationary state if and when the required amount of energy is absorbed by the electron. Energy is emitted when an electron moves from a higher stationary state to a lower stationary state. The energy change does not take place in a continuous manner.
- The frequency of radiation absorbed or emitted when transition occurs between two stationary states that differ in energy by ΔE is given by the following expression:
v = `(Δ"E")/"h"=("E"_2-"E"_1)/"h"` ......(1)
Where E1 and E2 are the energies of the lower and higher allowed energy states respectively. This expression is commonly known as Bohr’s frequency rule. - The angular momentum of an electron in a given stationary state can be expressed as mvr = `"n" × "h"/(2π)`
where, n = 1, 2, 3
Thus, an electron can move only in those orbits for which its angular momentum is an integral multiple of h/2π. Thus, only certain fixed orbits are allowed.
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