Rutherford's atomic model or atomic theory is one of the earlier atomic models. The model was proposed by Rutherford in 1911. It was a revolutionary at that time and made a major breakthrough in the atomic world.
Ernest Rutherford at McGill University in 1905
A brief history
In the 1900s, Thomson's atomic model was prominent. Thomson depicted an atom as a cloud of uniform positive charge with negatively charged electrons suspended in the cloud.
Some scientists did not agree with Thomson's theory, especially Hantaro Nagaoka, who was a Japanese physicist. In 1904, Nagaoka rejected Thomson's model and suggested a model similar to our planetary system. Nagaoka's predictions turned true when Rutherford had discovered the nucleus.
Ernest Rutherford was a New Zealand-born English Nobel laureates, also known as the father of nuclear physics. From 1908 to 1913, Rutherford along with his colleagues Hans Geiger and Ernest Marsden conducted a series of experiments, which is now called Rutherford's gold foil experiments. The observations of the experiments led him to discover the nucleus. In 1913, he affirmed the presence of the nucleus and formulated a new atomic model, which replaced a decade-old Thomson's theory.
Interesting facts: Rutherford is not only known for the discovery of the nucleus but also for the discovery of alpha, beta, and gamma rays. He was a student of J.J. Thomson, whom he proved wrong.
Postulates
On the basis of the results of the gold foil experiment, Rutherford proposed a nuclear model of the atom. It is described as follows:
Rutherford's atomic model: as we see, the electrons revolve around the nucleus, and most space in the atom is empty.
The atom is mostly empty.
The positive charge is concentrated at the centre of the atom. This centre is called as the nucleus of an atom.
Most mass of the atom is consolidated in the tiny nucleus. In other words, the nucleus of an atom is mostly responsible for the mass of an atom.
The magnitude of the positive charge is proportional to its atomic mass. Thus, the heavier the atom, the more charge it has.
Note: It was this central, heavy region that deflected alpha particles in the gold foil experiment.
The electrons in an atom are orbiting around this tiny nucleus similar to the planets around the sun in our solar system.Our solar system
Rutherford also determined the size of the gold atom and the size of its nucleus. He found that the nucleus is 105 times smaller than the atom itself. It is like a grain of sand placed at the centre of a soccer stadium.Jeonju world cup stadium in South Korea
Drawbacks
Although the model was successful in explaining the gold foil experiment, it has many limitations
Rutherford's model of the atom was unstable. According to Maxwell's classical electromagnetic theory, if a charged particle accelerates, it radiates energy. The energy is emitted in the form of electromagnetic waves. Thus, an electron revolving around the nucleus will lose the energy and its radius will keep shrinking until it collapses into its nucleus.The electron collapsing into the nucleusThe time taken for this collapse is estimated around 10−8 s, which is very small. According to the model, every atom will crumple in 10−8 s, but we know this is not reality.
If the electrons are not revolving but stationary, still the electrons will fall into the nucleus by the electrostatic force between both.
The model failed to mention the distribution of electrons and energy associated with them.
