Rutherford model of atom

Rutherford model of the atom experiment

Rutherford and his students study alpha particle scattering experiments. But the behavior of alpha particles in electric and magnetic fields which already established from the helium ion.

A beam of alpha particles directed to very thin platinum or gold foil which obtained from spontaneously disintegrating polonium.

With the help of fluorescent zinc sulfide screen around the platinum or gold foil and any deflection of the alpha particle was observed.

Rutherford model of atom
Rutherford model

Rutherford conclusion

The vast majority of the alpha particles passed the straight line through the foil. But a very limited few particles found to be deflected back from the foil. Some even appear on the side of incidence.

Rutherford concluded that since most of the alpha particles passed straight. Thus a very large volume of empty space in the atom of the platinum or gold.

But a very small part of the platinum or gold atom must be responsible for the large scattering of the few alpha particles. This central part called the atomic nucleus.

Gold foil experiment by Ernest Rutherford

Conclusions from the gold foil experiment

  1. All the positively charged and entirely mass of the atom concentrated in a very small part of the atom. These central core called the atomic nucleus.
  2. The large deflection of an alpha particle from its original path was due to Coulombic repulsion between the alpha particle and the positive nucleus of an atom. The simple impact between the two such massive particles can lead to a scattering of the order of only 10.
  3. Some alpha particle suffers little deflection while passing by an electron.
  4. The Radius of the atomic nucleus is ∼ 10-13 being the same as that of an electron. Since the radius of an atom ∼ 10-8, it is obvious that an atom must have a very empty structure. From the above conclusions, Rutherford proposed a structure of an atom.

Gold foil experiment results

According to Rutherford’s model, the entire mass of the atom was concentrated in a tiny positively charged nucleus.
And around which the extranuclear electrons were moving in a circular orbital.
Thus Rutherford divided the atom into two-part –

The nucleus of an atom

Almost the entire mass of the atom concentrated in a very small central core called the atomic nucleus.
Since the extranuclear electrons contribute negligibly to the total mass of the atom.

But an atom is electrically neutral, so it follows that the nucleus must carry particles that will account both for the mass and positive charge of the atom.

Extranuclear electrons definition

A very small positive nucleus considered surrounded by electrons. Such a system cannot be stable if the election were in rest.

Thus the electron moving in circular orbits around the nucleus and Coulombic attraction between the nucleus and the electron was equal to the centrifugal force of attraction.

Limitations of the Rutherford model

  1. The Rutherford model is not in conformity with the classical model of electromagnetic radiation. A moving charged particle emits radiation. Thus the loss of kinetic energy eventually will hit the nucleus.
  2. If the electrons lose energy continuously the observed atomic spectra should be continuous, which consisting of broad bands merging one into the other.