Difference Between Rutherford and Bohr Model

Main Difference – Rutherford vs Bohr Model

Rutherford model and Bohr model are models that explain the structure of an atom. Rutherford model was proposed by Ernest Rutherford in 1911. Bohr model was proposed by Niels Bohr in 1915. Bohr model is considered as a modification of Rutherford model. The main difference between Rutherford and Bohr model is that Rutherford model does not explain the energy levels in an atom whereas Bohr model explains the energy levels in an atom.

Key Areas Covered

1. What is Rutherford Model
      – Definition, Explanation of the Model
2. What is Bohr Model
      – Definition, Explanation of the Model
3. What is the Difference Between Rutherford and Bohr Model
      – Comparison of Key Differences

Key Terms: Alpha Particles, Atom, Bohr Model, Electron, Line Spectra, Nucleus, Orbitals, Rutherford Model

What is Rutherford Model

Rutherford model of atom describes that an atom is composed of a central core and nearly all mass of that atom is concentrated and light weight particles move around this central core. It also states that the central core is positively charged and constituents that move around the central core are negatively charged.

Figure 1: Structure of Atom as Suggested by Rutherford

This model was experimentally observed by Ernest Rutherford via the famous “Rutherford gold foil experiment”. In this experiment, alpha particles were bombarded through a gold foil; they were expected to go straight through the gold foil. But instead of straight penetration, alpha particles turned into different directions.

In order to explain this model, Rutherford suggested the followings.

• An atom is composed of a central core which has a positive charge.
• Negatively charged constituents are located around this central core.
• Positive and negative charges balance with each other.

However, this Rutherford model of atom was also rejected because it couldn’t explain why electrons and the positive charges in the nucleus are not attracted to each other.

What is Bohr Model

Bohr model is a modification of the Rutherford model. This model was proposed based on the line spectra of the hydrogen atom. This model proposed that electrons are always traveling in specific shells or orbits around the nucleus. Bohr model also indicated that these shells have different energies and are spherical in shape.

Furthermore, Bohr model explained that electrons in one orbital can move to different orbital by either absorbing energy or releasing energy.

Figure 2: Atomic Structure according to Bohr Model

The line spectra of hydrogen atom had many discrete lines. In order to explain this spectrum, Bohr suggested the followings.

• Electrons move around the nucleus in certain shells or
• These shells have discrete energy levels.
• The energy of an orbit is related to the size of the orbit. Smallest orbit has the lowest energy.
• Electrons can move from one energy level to another.

Although this model perfectly fits the atomic structure of hydrogen atom, there were certain limitations when applying this model to other elements. One such limitation is the inability to explain the Zeeman effect and Stark effect observed in line spectra.

Difference Between Rutherford and Bohr Model

Definition

Rutherford Model: Rutherford model states that an atom is composed of a central core where nearly the whole mass of that atom is concentrated, and light weight particles move around this central core.

Bohr Model: Bohr model explains that the electrons always travel in specific shells or orbits which are located around the nucleus and these shells have discrete energy levels.

Observation

Rutherford Model: Rutherford model was developed based on observations of gold foil experiment.

Bohr Model:  Bohr model was developed based on observations of line spectra of the hydrogen atom.

Energy Levels

Rutherford Model: Rutherford model does not describe the presence of discrete energy levels.

Bohr Model: Bohr model describes the presence of discrete energy levels.

Size of Orbitals

Rutherford Model: Rutherford model does not explain the relationship between orbital size and the energy of the orbital.

Bohr Model: Bohr model explains the relationship between orbital size and the energy of the orbital; smallest orbital has the lowest energy.

Conclusion

Both Rutherford model and Bohr model explain the same concept of atomic structure with slight variations. The main difference between Rutherford model and Bohr model is that Rutherford model does not explain the energy levels in an atom whereas Bohr model explains the energy levels in an atom.

References:

1. “Rutherford atomic model.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 10 Aug. 2017, Available here.
2. Helmenstine, Anne Marie. “What is the Bohr Model of the Atom?” ThoughtCo, Available here.
3. “The Bohr Model”, University of Rochester. Available here.

Image Courtesy:

1. “Rutherford atom” By Own work (CreateJODER Xd Xd) (CC BY-SA 3.0) via Commons Wikimedia
2. “Bohr atom model English” By Brighterorange – Created by Brighterorange, based on GFDL/cc image: Bohratommodel.png. (CC BY-SA 3.0) via Commons Wikimedia