What are the Defects of Bohr’s Atomic Model?
In 1913 Neil Bohr’s presented a new model for an atom, known as Bohr’s atomic model. It has the following defects:
1. Spectrum of poly electrons atoms:
Bohr’s atomic model cannot explain the spectrum of complicated (poly electrons) atoms.
It only explains the spectrum of H-atom and hydrogen-like ions. e.g. He+, Li +2, Be +3.
All these ions have one electron like hydrogen.
2. Fine structure of the Hydrogen spectrum:
It cannot explain the fine structure of the hydrogen spectrum.
For example, when the hydrogen spectrum is observed by a powerful spectrometer, the Balmer series consists of five components.
3. Motion of electrons :
Bohr model cannot explain the motion of electrons in three-dimensional space.
It only explains that electrons revolve in circular paths called orbits around the nucleus in a single plane but it is proved that the electrons are in three-dimensional space, not in a single plane.
It gives no idea of the distribution and arrangement of electrons around the nucleus of an atom.
4. Zeeman Effect and Stark Effect:
Bohr’s theory cannot explain Zeeman Effect or Stark Effect.
When the excited hydrogen atom is placed in a strong magnetic field then the spectral lines further split into more fine lines. The splitting of spectral lines is called Zeeman Effect.
Similarly when the excited hydrogen atom is placed in a strong electrical field spectral lines of the hydrogen atom split up into more fine lines by applying an electric field. It is called the Stark effect.
5. Exact position and velocity of an electron:
Bohrs assumes the exact position and velocity of an electron simultaneously which is not possible.
According to Heisenberg’s uncertainty principle, both the exact position and velocity of an electron cannot measure simultaneously so Bohr’s picture of an atom is not satisfactory.
To solve this problem, Schrodinger gave a wave equation for a hydrogen atom.
Bohr’s Atomic Model