3 Postulates of Rutherford's atomic model (1911)

From this and other experiments Rutherford proposed:

1. The atom has an extremely small size but a complex structure resembling the solar system: a central nucleus (like the Sun) around which the electrons revolve (like planets).
2. The nucleus is much smaller than the atom, with a vast space between it and the electron orbits (so the atom is not solid). It is positively charged and most of the atom's mass is concentrated in it.
3. The electrons
   • have a very small mass, negligible compared with the nucleus;
   • their total negative charge equals the positive charge of the nucleus, so the atom is electrically neutral;
   • orbit the nucleus at high speed in definite orbits. The attraction between nucleus and electrons is balanced by an equal and opposite (centrifugal) force, so the electron does not fall into the nucleus.

Limitation.

• Rutherford's model did not explain the arrangement (system) in which the electrons move around the nucleus, nor the line spectra of elements.
• This was solved in part by Bohr.

Summary table