Rutherford’s Atomic Model and its Limitations

An atom contains electrons, neutrons, and protons. The structure of atoms has been formulated by many scientists. But the most favourable and well-explained model was given by scientist Ernest Rutherford. This model is recognized as Rutherford’s atomic model. So, let us discuss in detail Rutherford’s atomic model and their limitations, his theories, and experiments.

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Atomic Model of Rutherford:

Firstly, a plum pudding model on the atomic structure was suggested by JJ Thomson. Due to a lack of experimental evidence, it was not accepted. But, Ernest Rutherford successfully researched the structure of atoms and proposed the atomic structure of the elements.

In his experiment with the elements, he fired a beam of alpha particles at a thin foil of gold and observed the trajectory of those particles.

Rutherford’s Alpha Scattering Experiment:

Rutherford took 100mm gold sheets to bombard high-energy alpha particles during his experiment. The alpha particles were seen from a radioactive stream. His main aim was to study the deflections of the alpha particles after it’s interaction with the thin sheet of gold generated in the trajectory. He then placed a screen made up of zinc sulphide around the gold sheet to observe the deflection. His experimental results were contradictory to that of the pudding method proposed by JJ Thomson.

Observations of Rutherford in his alpha scattering experiment:

His views after his experimentation with alpha particles are noted below:

1. After his observations in the experiment, he concluded that the maximum space of the atoms is empty. During the experimentation, a major part of the alpha particles passed through the gold foil undeflected.
2. Some alpha particles get deflected. However, the particles were deflected at negligible angles and therefore, positive charge is not uniformly distributed in an atom. A very small volume of the atom is concentrated with positive charges.
3. There were very few alpha particles that showed higher angle deflections. Also, very few of them deflected at 180° angles. This confirmed that a smaller portion of the atom has positive charges.

Differences between atomic models of Rutherford and JJ Thomson:

JJ Thomson proposed the structure of the atoms much earlier than other scientists. According to him, atoms are shaped like spheres, and their radius is near 10-10m  with a uniform distribution of the positive charges. In this sphere of the atom’s, electrons are embedded and maintain stable electrostatic configurations.

Since the electrons of the Thomson’s model looked like raisins in a pudding, it was named the plum pudding model. This model explains that there is a uniform mass distribution over the atoms. 

Based on Rutherford’s observations and conclusions the atomic models are-

• There is a small region in the atoms which is densely surrounded by positive energy. Rutherford named this region the nucleus of the atom.
• The electrons move around the nucleus at higher speeds following circular paths known as orbits. We can refer to the solar system for further understanding of this model as this arrangement resembles the solar system. If we assume the nucleus is the sun, the electrons become the planets revolving around the sun. Hence, we can call this model a planetary model too.
• The electrons and the nucleus are held together with the help of electrostatic forces.

Rutherford’s postulates on the atomic model based on his experimentation:

• An atom is composed of positively charged particles. The majority of this positive charge is concentrated in a small region called the nucleus of the atom. The fact that the nucleus consists of neutrons and protons was found much later.
• The nucleus of the atoms is surrounded by many negatively charged particles termed as electrons. These electrons move around the nucleus at faster rates in circular orbits.
• The atoms are neutral. They don’t have any net charge as the electrons are negatively charged, and the dense nucleus is positively charged. A strong electrostatic force of attraction acts on it to hold it together, and hence they are electrically neutral.
• The size of the nucleus of an atom is very small when compared to the full size of an atom.

Limitations of Rutherford’s atomic model:

Rutherford’s atomic model was accepted and experimentally successful, but it could not explain certain important things about atoms.

Let us discuss in detail these drawbacks of Rutherford’s atomic model-

1. His theory and model were not able to explain the stability of the atoms. According to Rutherford’s observation, the electrons in an atom move at higher speeds around its nucleus in circular orbits. This contradicted Maxwell’s observations. Maxwell explained that the charged particles in the atoms are accelerated, and they release electromagnetic radiation. Thus, the electrons moving around the nucleus in an atom must emit electromagnetic radiation. These facts are not explained in the Rutherford atomic model.
2. The orbits made by the electrons will shrink due to the electromagnetic radiation. These electromagnetic radiations have energy due to electronic motion. As a result of this, the orbits will collapse in the nucleus. And if we compare this with Maxwell’s theory then the nucleus will collapse within 10-8 seconds. And therefore, we can say that Rutherford’s model does not comply with Maxwell’s theory, and it fails to explain the stability of the atoms.
3. Rutherford’s atomic model does not explain any arrangement of electrons in the orbit, and hence, it remains incomplete. And this can be one of the major limitations of Rutherford’s atomic model.

Conclusion:

This model was successful in explaining the nature of neutrality of atoms, but its propositions were not correct when matched with later experimental results. However, Rutherford was successful in explaining the true nature of atoms, and his theory was accepted by all.

While there are many limitations of the Rutherford atomic model, Rutherford was successful in explaining the true nature of atoms, and his theory was accepted by all. Rutherford’s atomic model first gave the idea of the structure of atoms. It marked the basis of quantum mechanics. The Rutherford atomic model also helped in the further development of quantum mechanics.