Drawbacks of Rutherford's Atomic Model

Rutherford Atomic model is also known as the Rutherford model, nuclear atom, or planetary model of the atom was established in the year 1911 which explained the structure of atoms and was developed by the New Zealand-born physicist Ernest Rutherford. The model derived that the atom is nothing but a small tiny dense mass that has a positively charged body present in the core which is presently known as the nucleus where the entire mass of the atom is concentrated and around it revolves the negatively charged light electrons at a certain distance much like the planets revolving around the sun. 

In the gold foil experiment, the nucleus was postulated as a dense and small mass which was responsible for the scattering of the alpha particles. It was observed in a series of experiments that were carried out by the undergraduate Ernest Marsden under the guidance of Rutherford and German physicist Hans Geiger in 1909. The Rutherford model as a supplement for the  “plum-pudding” atomic model of English physicist Sir J.J. Thomson worked on the fact claimed by the plum-pudding atomic model that the electrons are embedded into the positively charged mass that was claimed as the atom-like plums in a pudding. 

Rutherford's model was also obsoleted by Bhor’s atomic model purely based on classical physics. Bohr’s atomic model has also been seen to be incorporating some of the early concepts of quantum theory.     

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Rutherford’s Alpha Scattering Experiment Explanation

Rutherford conducted a light scattering experiment where he placed a gold foil and bombarded the gold sheet with the alpha particles. The trajectory of the alpha particles was then studied after they interacted with the gold foil. There was a radioactive source that emitted Alpha particles which are positively charged particles that were enclosed within a lead shield in a protective manner.

The radiation then passed in a narrow beam after it passed through a slit which was made in the lead screen. A very thin section of a gold foil is placed before the lead screen and the LED screen was covered with zinc sulphide so as to give it a fluorescent nature that served as a counter detection to the Alpha particles. 

As soon as the Alpha particles right the fluorescent screen it's shattered into a burst of light which is known as scintillation. It was visible from the viewing microscope that was attached to the back of the screen. As the screen was movable, it allowed Rutherford to study whether or not Alpha particles get deflected by the gold foil.

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Observations of Rutherford’s Alpha Scattering Experiment

The observation that was made by Rutherford let him conclude that:-

1. Most of the Alpha particles that bombarded the gold fell passed through without any deflection that shows that the nucleus is made up of a large empty space.

2. Few of the Alpha particles that bombarded against the gold foil experienced a very minor deflection that shows that there is a presence of a counter positive charge.

3. Still, some of the Alpha particles that bombarded against the gold foil deflected to a larger angle and some of them even bounced back showing that the positive charge is concentrated in a very small volume and its distribution is non-uniform.

4. All the above points show that the volume occupied by positively charged particles in an atom is very small as compared to the total volume of the atom.

Result of Rutherford’s Alpha Scattering Experiment 

On the basis of his experiment, observation and result, Rutherford put forward Rutherford’s atomic model, which had the following features:

• The entire mass and positive charge of an atom are concentrated in a very small region at the centre known as the nucleus. 

• The positive charge on the nucleus is due to protons. Since the number of protons is different for atoms of different elements, therefore, the magnitude of positive charge on the nucleus is different for atoms of different elements. 

• The nucleus is surrounded by negatively charged electrons. The number of electrons in an atom is equal to the number of protons (positively charged) in the nucleus. Thus, the atom as a whole is neutral. 

• The electrons are revolving around the nucleus at a very high speed. 

• Most of the space in an atom is empty.

Drawbacks of Rutherford’s Atomic Model

Rutherford’s Atomic Model had the Following Limitations:

• This atomic model failed to explain the stability of atoms.

• According to the model, electrons revolve around the positively charged nucleus. It's not possible for the long run as we know atoms are stable while any particle in a circular orbit would undergo acceleration. During acceleration charged particles would radiate energy. Revolving electrons will lose energy and finally fall into the nucleus. 

• This model of the atom also failed to explain the existence of definite lines in the hydrogen spectrum.

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