# Difference Between Thomson and Rutherford Model of Atom

## Main Difference – Thomson vs Rutherford Model of Atom

Thomson model of atom is one of the earliest models to describe the structure of atoms. This model is also known as the plum pudding model due to its resemblance to a plum pudding. This explains that this atom is a spherical structure made out of a positively charged solid material and the electrons are embedded in that solid. But this model was rejected after the discovery of atomic nucleus. Rutherford model of atom describes the atomic nucleus and the location of electrons in an atom. It was proposed who described that an atom is composed of a central solid core which is positively charged and electrons are located surrounding this solid core. However, this model was also rejected because it could not explain why the electrons are not attracted to the nucleus. The main difference between Thomson and Rutherford model of atom is that Thomson model does not give details about the atomic nucleus whereas Rutherford model explains about the nucleus.

### Key Areas Covered

1. What is Thomson Model of Atom
– Definition, Model, Drawbacks
2. What is Rutherford Model of Atom
– Definition, Model, Drawbacks
3. What is the Difference Between Thomson and Rutherford Model of Atom
– Comparison of Key Differences

Key Terms: Alpha Particles, Atom, Electron, Gold Foil Experiment, Nucleus, Plum Pudding Model, Rutherford Model of Atom, Thomson Model of Atom

## What is Thomson Model of Atom

Thomson model of atom is the structure of an atom proposed by the scientist, J.J.Thomson, who was the first person to discover the electron. Soon after the discovery of the electron, the atomic model was proposed saying that the structure of an atom is like a “plum pudding”.

Thomson model of atom is described base on three main facts:

• Atoms are composed of electrons.
• Electrons are negatively charged particles.
• Atoms are neutrally charged.

Figure 1: Thomson Model of Atom

Thomson proposed that since electrons are negatively charged and atoms are neutrally charged, there should be a positive charge in the atom in order to neutralize the negative charge of electrons. He proposed that the atom is a solid, positively charged, spherical structure and electrons are embedded in that sphere. Since this structure looks like a pudding with plums scattered on it, it was called the plum pudding structure of atom. However, this structure was rejected after the discovery of atomic nucleus.

### Drawbacks of Thomson Model of Atom

• No details about atomic nucleus.
• No details about atomic orbitals.
• No explanation about the protons or neutrons.
• States that the atom has a uniform distribution of mass, which is wrong.

## What is Rutherford Model of Atom

Rutherford model of atom describes that the atom is composed of an atomic nucleus and electrons surrounding the nucleus. This model caused to reject the Thomson model of atom. Rutherford model was proposed by Ernst Rutherford after the discovery of the atomic nucleus.

The gold foil experiment was used by Rutherford to propose this atomic model. 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. This experiment indicated that there is a positively charged, solid material in the middle of the atom while the rest of the atom has more empty space. This solid core was named as the nucleus.

Figure 2: Rutherford Atomic Model

According to this model,

• The atom is composed of a positively charged center which is called the nucleus. This center contained the mass of the atom.
• Electrons are located outside the nucleus in orbitals at a considerable distance.
• The number of electrons is equal to the number of positive charges (later called protons) in the nucleus.
• The volume of the nucleus is negligible when compared to the volume of the atom. Hence, most of the space in the atom is empty.

### Drawbacks of Rutherford Model of Atom

Later, Rutherford model was also rejected because it could not explain why the positively charged nucleus and electrons are not attracted to each other.

## Difference Between Thomson and Rutherford Model of Atom

### Definition

Thomson Model of Atom: Thomson model of atom states that electrons are embedded in a positively charged solid material which is spherical in shape.

Rutherford Model of Atom: Rutherford model of atom describes that an atom is composed of an atomic nucleus and electrons surrounding the nucleus.

### Nucleus

Thomson Model of Atom: Thomson model of atom does not give any details about the atomic nucleus.

Rutherford Model of Atom: Rutherford model of atom explains about the atomic nucleus.

### Electrons

Thomson Model of Atom: Thomson model of atom states that electrons are embedded in a solid material.

Rutherford Model of Atom: Rutherford model of atom states that electrons are located around a central solid material.

### Shape of Atom

Thomson Model of Atom: Thomson model of atom indicates that the atom is a spherical structure.

Rutherford Model of Atom: Rutherford model of atom indicates that an atom has a central solid core surrounded by electrons.

### Conclusion

Thomson model of atom and Rutherford model of atom are two models proposed by J.J.Thomson and Ernest Rutherford, respectively in order to explain the structure of an atom. The main difference between Thomson and Rutherford model of atom is that Thomson model does not give details about the atomic nucleus whereas Rutherford model explains about the nucleus.

##### References:

1. “Thomson Atomic Model & its Limitations | Development Of Atomic Model.” Chemistry, Byjus Classes, 7 Nov. 2017, Available here.
2. “Thomson atomic model.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 27 Dec. 2013, Available here.
3. “Geiger–Marsden experiment.” Wikipedia, Wikimedia Foundation, 8 Nov. 2017, Available here.

##### Image Courtesy:

1. “PlumPuddingModel ManyCorpuscles” By Tjlafave – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Rutherfordsches Atommodell” (Public Domain) via Commons Wikimedia