Definition of the Rutherford Model
The Rutherford atomic model has 2 main parts: the nucleus, and the atom’s remaining space, occupied by electrons.
According to the model, the nucleus is a very small portion of the atom’s volume. It occupies a small space in the very center of the atom. Protons and neutrons make up the nucleus and define the atom’s chemical properties.
Rutherford also claimed in his model that electrons revolved around the nucleus in set orbits, like planets revolving around the Sun. This part of the theory was inaccurate, as explained in the last section.
Rutherford’s Gold Foil Experiment
The Rutherford gold foil experiment, also known as the scattering experiment, led to the creation of the model and explained the parts of the atom. In 1909, graduate student Ernest Marsden (under Ernest Rutherford’s supervision) fired alpha particles at a gold foil piece. Most of the particles passed directly through the foil, meaning that a majority of the space in each atom was unoccupied. However, a few particles were deflected, and some even backward. This must have been caused by tiny pockets of positive charge in the foil repelling the alpha particles back. Their discovery led to the creation of Rutherford’s model, in which the dense, positively-charged nucleus occupies a very small area in the center of each atom.
Shortcomings of the Rutherford Model
While common models today are based on the Rutherford atomic theory, it does not paint the complete picture:
- The model is missing parts and does not account for the location or distribution of electrons.
- Rutherford proposed that electrons orbit around the nucleus in set paths, but according to Maxwell’s theory, this is not possible because the atom would not be stable. Electromagnetic radiation from the electrons in orbit would cause the atom to collapse into the nucleus in 10-8 seconds.
- Electrons increase and decrease energy levels randomly due to the acceleration and are not always in a standard circular orbit. They give off electromagnetic radiation due to the circular motion of orbiting; thus they must have some initial energy by the law of conservation of energy. The Rutherford atomic model does not account for the initial energy and subsequent energy level changes.