The Rutherford model or planetary model is a model of the atom devised by Ernest Rutherford. Rutherford directed the famous Geiger-Marsden experiment in 1909, which suggested on Rutherford's 1911 analysis that the so-called "plum pudding model" of J. J. Thomson of the atom was incorrect. Rutherford's new model[1] for the atom, based on the experimental results, had the new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and containing the bulk of the atomic mass (the nucleus of the atom).
Rutherford's model did not make any new headway in explaining the electron-structure of the atom; in this regard Rutherford merely mentioned earlier atomic models in which a number of tiny electrons circled the nucleus like planets around the sun, or a ring around a planet (such as Saturn). However, by implication, Rutherford's concentration of most of the atom's mass into a very small core made a planetary model an even more likely metaphor than before, as such a core would contain most of the atom's mass, in an analogous way to the Sun containing most of the solar system's mass. Rutherford's model was later corrected by Niels Bohr.
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In 1911, Rutherford came forth with his own physical model for subatomic structure, as an interpretation for the unexpected experimental results. In it, the atom is made up of a central charge (this is the modern atomic nucleus, though Rutherford did not use the term "nucleus" in his paper) surrounded by a cloud of (presumably) orbiting electrons. In this May 1911 paper, Rutherford only commits himself to a small central region of very high positive or negative charge in the atom.
"For concreteness, consider the passage of a high speed α particle through an atom having a positive central charge N e, and surrounded by a compensating charge of N electrons." [2]
From purely energetic considerations of how far particles of known speed would be able to penetrate toward a central charge of 100 e, Rutherford was able to calculate that the radius of his gold central charge would need to be less (how much less could not be told) than 3.4 x (the modern value is only about a fifth of this). This was in a gold atom known to be 10−10 metres or so in radius—a very surprising finding, as it implied a strong central charge less than 1/3000th of the diameter of the atom.
The Rutherford model served to concentrate a great deal of the atom's charge and mass to a very small core, but didn't attribute any structure to the remaining electrons and remaining atomic mass. It did mention the atomic model of Hantaro Nagaoka, in which the electrons are arranged in one or more rings, with the specific metaphorical structure of the stable rings of Saturn. The so-called plum pudding model of J.J. Thomson had also had rings of orbiting electrons.
The Rutherford paper suggested that the central charge of an atom might be "proportional" to its atomic mass in hydrogen mass units u (roughly 1/2 of it, in Rutherford's model). For gold, this mass number is 197 (not then known to great accuracy) and was therefore modeled by Rutherford to be possibly 196 u. However, Rutherford did not attempt to make the direct connection of central charge to atomic number, since gold's place on the periodic table was known to be about 79 u, and gold's "atomic number" (at that time merely its place number in the periodic table) that Rutherford did not formally suggest the two numbers (atomic number and nuclear charge) might be exactly the same.
A month after Rutherford's paper appeared, the proposal regarding the exact identity of atomic number and nuclear charge was made by Antonius van den Broek, and later confirmed experimentally within two years, by Henry Moseley.
After Rutherford's discovery, scientists started to realize that the atom is not ultimately a single particle, but is made up of far smaller subatomic particles. Following research was done to figure out the exact atomic structure which led to Rutherford’s gold foil experiment. They eventually discovered that atoms have a positively-charged nucleus (with an exact atomic number of charges) in the center, with a radius of about 1.2 x 10−15 meters x [Atomic Mass Number]1/3. Since electrons were found to be even smaller, this meant that the atom consists of mostly empty space.
Later on, scientists found the expected number of electrons (the same as the atomic number) in an atom by using X-rays. When an X-ray passes through an atom, some of it is scattered, while the rest passes through the atom. Since the X-ray loses its intensity primarily due to scattering at electrons, by noting the rate of decrease in X-ray intensity, the number of electrons contained in an atom can be accurately estimated.
Despite its inaccuracy, the Rutherford model caught the imagination of the public in a way that the more correct Bohr model did not, and has continually been used as a symbol for atoms and atomic energy. Examples of its use over the past century include:
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