Structure of Atom — Chemistry STD 11 Science — Question

ii. 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 electron moves from a higher stationary state to a lower stationary state. The energy change does not take place in a continuous manner.

iii. 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:

$v=\frac{\Delta E}{h}=\frac{E_2-E_1}{h}$

Where $E_1$ and $E_2$ are the energies of the lower and higher allowed energy states respectively. This expression is commonly known as Bohr's frequency rule.
iv. The angular momeñtum of an electron in a given stationary state can be expressed as $m v r=n \times h / 2 \pi$ where, $n 1,2,3$
Thus, an electron can move only in those orbits for which its angular momentum is integral multiple of $h / 2 \pi$.
Thus, only certain fixed orbits are allowed.