Ernest Rutherford’s Model of an Atom
Structure of an atom includes electrons, protons, and neutrons. In history, several scientists had come up with different models of an atom. The classic model presented by Ernest Rutherford came to be known as the Rutherford atomic model. It should be noted that it is no longer considered the accurate representation of an atom.
An atom is composed of empty space. The electrons will orbit in a set, expected path around a fixed, positively charged nucleus.
The concept of an atom was introduced by Greek philosopher Democritus in 400 BCE. A new idea of the atom was proposed by John Dalton in 1803. Atoms were considered indivisible particles until 1897. Negatively charged particles (electrons) were discovered by British Physicist J.J. Thomson.
J.J. Thomson’s model of an atom was called the plum pudding model. It had certain limitations. As per the model, electrons were embedded in a uniformly charged matrix.
Rutherford conducted an experiment in which he bombarded α-particles in a thin sheet of gold. He observed the trajectory of the α-particles after their interaction with the thin sheet of gold.
In the experiment, high energy streams of α-particles were bombarded on a thin gold foil of 100 nm thickness. The α- particles were directed from a radioactive source. Rutherford conducted the experiment for studying the deflection produced in the trajectory of α- particles post their interaction within the thin sheet of gold. Inorder to study the deflection, a screen made up of zinc sulfide was placed around the gold foil. His observations were in contradiction to the plum pudding model given by J.J. Thomson.
After the experiment, Rutherford observed that,
- Major fraction of α-particles passed through the gold sheet without any sort of deflection. This suggests that a large part of an atom is empty.
- The positive charge inside an atom is not distributed uniformly. It is rather concentrated in a very small volume.
- Since very few α-particles deflected at large angles or deflected back, Rutherford came to the conclusion that positively charged particles cover only a small volume of an atom, compared to the total volume of an atom.
- It was discovered that the very small and dense nucleus of an atom consists of neutrons and protons.
- It was noted that electrons revolve around the nucleus in a fixed circular path at very high speed. The circular paths were called ‘orbits’.
- An atom is electrically neutral. It was noted that a strong electrostatic force of attraction holds together the nucleus and electrons.
- The nucleus of an atom is very small when compared to the total size of an atom.
There were certain things that Rutherford’s experiment was unable to explain.
- Rutherford’s experiment failed to explain the stability of an atom. According to J.C. Maxwell, electrons revolving around the nucleus will release electromagnetic radiation. Rutherford’s model did not take this aspect into consideration.
- In short, Rutherford’s model of an atom was not following Maxwell’s theory and was unable to explain the stability of an atom.
- In fact, nothing was mentioned about the arrangement of electrons in the orbit. This was considered as one of the major shortcomings of Rutherford’s atomic model.
The early atomic models proved inaccurate and failed to explain the structure of an atom and the experimental results in a proper manner. However they formed the basis of quantum mechanics which proved useful in the later years.
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Check your knowledge
Answer) Protons, neutrons and electrons.
Answer) J.J. Thomson.
Answer) Zinc Sulfide.