Models of atoms: Limitation of Rutherford’s model

Introduction

An atom contains electrons, neutrons, and protons. 

Many scientists have formulated the structure of atoms. But the most fundamental and well-explained model was given by scientist Ernest Rutherford. This model is Rutherford’s atomic model. 

So, let us discuss Rutherford’s atomic model and its limitations, theories, and experiments in detail.

Atomic Model of Rutherford

1904. J. Thomson suggested a plum pudding model of the atomic structure in 1904. However, the model couldn’t hold because of a lack of experimental evidence.  

Later in 1911, physicist Ernest Rutherford conducted his famous alpha scattering experiment to study the Thomson model. In his investigation, he fired a beam of alpha particles at a thin foil of gold and observed the trajectory of those particles. Based on his inferences, he proposed a structural model for the atom.

Differences between atomic models of Rutherford and JJ Thomson:

According to Thomson, atoms have a spherical shape, and their radius is near 10-10 m with a uniform distribution of the positive charges. In this sphere of the atoms, electrons are embedded and maintain stable electrostatic configurations.

Since the electrons of 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. 

On the other hand, Rutherford’s model finds similarities with the solar system’s arrangement. Hence, it is also called the planetary model of atoms. 

As per him, the nucleus occupies the atom’s centre with the electrons surrounding it. The nucleus comprises positively charged particles, while the electrons have a negative charge. Overall, the atom has a net-zero charge. Further, the concentration of the atomic mass is in the nucleus.

Models of an Atom: Limitations of Rutherford’s Model

Rutherford’s atomic model was experimentally successful and found acceptance within the scientific community. However, it could not explain certain vital things about atoms.

Let us discuss in detail the limitations of Rutherford’s atomic model.

1. His theory and model could not 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 behaviour contradicted Maxwell’s observations. Maxwell explained that the acceleration of the charged particles in the atoms causes them to release electromagnetic radiation. Thus, the electrons moving around the nucleus in an atom must constantly emit electromagnetic radiation. Rutherford’s atomic model did not explain these facts.
2. The electromagnetic radiations of the electron have energy due to their kinetic motion. However, it will cause their orbit to shrink as they continuously emit energy and collapse in the nucleus. And if we compare this with Maxwell’s theory, it will happen 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 orbit, so it remains incomplete. It is one of the major limitations of Rutherford’s atomic model.
4. An atom is composed of positively charged particles. A small region in the atom, called the nucleus, concentrates most of this positive charge. Later discoveries of protons and neutrons nullify this hypothesis of the Rutherford model. 
5. Many negatively charged particles termed electrons surround the nucleus of the atoms. These electrons move around the nucleus at faster rates in circular orbits. Again, later research disproved this assumption. 

Conclusion

This model correctly surmised the nature of neutrality of atoms, but its propositions were not correct when matched with later experimental results. 

Apart from this fact, the model contradicted Maxwell’s theory and also could not find out why atoms don’t emit a linear spectrum. However, Rutherford successfully explained the true nature of atoms, and everyone accepted his theory.

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.