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.

Niels Bohr model describes an atom as a small positively charged nucleus surrounded by electrons that travel in circular orbits around the positively charged nucleus like planets around the sun in our solar system, with electrostatic forces providing attraction. This model is popularly known as Bohr’s atomic model. Essentially, it was an enhanced version of Rutherford’s atomic model that overcame its constraints.

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Drawbacks of Niels Bohr’s atomic model

Bohr’s atomic model has the following defects(drawbacks):

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’s 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.

Recommended video!

Bohr Model Video Lecture

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Frequently Asked Questions – FAQs

What is the limitation of Bohr Atomic Model Theory?

Bohr was the first to discover that electrons move in distinct orbits around the nucleus and that the number of electrons in an element’s valence shell determines its properties.

How do electrons move in Bohr’s model?

According to Bohr, electrons move in a fixed circular orbit around the central nucleus. These circles of distinct energies are also known as energy levels or energy shells.

What is the significance of Bohr Atomic Model Theory?

Bohr was the first to discover that electrons move in distinct orbits around the nucleus and that the number of electrons in an element’s valence shell determines its properties.

How did Bohr discover electrons?

Bohr was the first to discover that electrons move in distinct orbits around the nucleus and that the quantity of electrons in the outer orbit determines an element’s properties.

What were the weaknesses or limitations of Bohr’s model?

Bohr’s atomic model has certain limitations:

• It defies Heisenberg’s uncertainty principle, which says an electron’s position and momentum can’t be accurately computed simultaneously. Bohr’s atomic model theory assumes electrons have a defined radius and orbit, which Heisenberg says is impossible.
• The Bohr atomic model hypothesis correctly predicted smaller atoms like hydrogen, while larger atoms had poor spectrum predictions.
• It didn’t explain the Zeeman effect when a magnetic field splits a spectral line.
• It didn’t explain the Stark effect, in which an electric field splits spectral lines into fine lines.
• Schrodinger’s equation yields the quantum mechanical atom model. The solution requires quantization of electron energy. In the Bohr model, quantization was assumed without math. Wave functions offer the chance of finding an electron at a certain position around the nucleus. Electrons don’t orbit the nucleus in circles.

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