Question

Which of the following are true according to the postulates of Bohr's theory?

• A. When an atom gets the required energy from outside, it jumps from lower orbits to higher orbits and remains there forever.
• B. When an atom gets the required energy from outside, it jumps from the lower orbit to a higher orbit and remains there for very short intervals of time and returns back to a lower orbit, radiating energy.
• C. Angular momentum of an electron is proportional to $n$.
• D. Angular momentum of an electron is independent of $n$.

Answer 1

Answer: (B), (C)

Angular momentum of an electron is proportional to $n$.

The main postulates of Bohr's theory was:

a. The electron in the hydrogen atom revolves around the nucleus in a circular path of fixed radius and energy. These paths are called orbits, stationary states, energy shells, or allowed energy states. These stationary states for electrons are numbered as n = 1, 2, 3, . . . . . or designated as K, L, M, N, . . . . . etc. shells. These integral numbers are known as principal quantum numbers. These orbits are arranged concentrically around the nucleus.

b. Electrons revolve only in those orbits where the angular momentum of the electron is quantized. Thus an electron can move only in those orbits for which its angular momentum is an integral multiple of h/2π that is why only certain fixed orbitals are allowed.

$m_{e}vr$ = $\frac{nh}{2\pi }$, or $r$ = $\frac{nh}{2m_{e}v\pi }$ (where $n=1,2,3andsoon.$)

d. The electron will move from a lower stationary state to a higher stationary state when the required amount of energy is absorbed by the electron. It stays in the excited energy level (higher-energy stationary orbit) for a very brief while. The electron jumps back (de-excites) to the lower energy level while emitting the same amount of energy.