Lord Rutherford’s Atomic model

Rutherford’s model of an atom:

• Rutherford carried out an experiment where fast-moving alpha particles were made to fall on a thin gold foil. The following were his observations:
• Most of the fast moving α-particles passed straight through the gold foil.
• Some of the α-particles were deflected by the foil by small angles.
• Surprisingly one out of every 12000 particles appeared to rebound.

Following were his conclusions from the α-particle scattering experiment:

1. Most of the space inside the atom is empty because most of the α-particles passed through the gold foil without getting deflected.
2. Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.
3. A very small fraction of α-particles were deflected by 1800, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

On the basis of his experiment, Rutherford put forward the nuclear model of an atom, which had the following features:

• There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus.
• The electrons revolve around the nucleus in circular paths.
• The size of the nucleus is very small as compared to the size of the atom.

Drawbacks of Rutherford’s model of the atom:

• Was unable to explain the stability of an atom.
• The theory was incomplete as it did not mention anything about the arrangement of electrons in the orbit.
• Failed to explain line spectra of an atom.