Greek philosopher Democritus was curious to know that a piece of matter can be cut into how many smaller pieces? He thought that it would reach a point where it could not be cut into still smaller pieces. He called these smallest pieces of matter “atomos”. This is an incident of around 450 B.C. However, the idea was forgotten for more than 2000 years. Then, British Chemist John Dalton revived the idea of atom in 1800 and provided evidence for atoms in matter. After the discovery of atom many atomic models were suggested by scientists to describe its structure and discovery of subatomic particles – electron, proton and neutron took place. It was around 1911, when Rutherford discovered the nucleus and suggested Rutherford’s Atomic Model.
On the basis of his experiment, observation and result, Rutherford put forward Rutherford’s atomic model, which had following features –
The entire mass and positive charge of an atom is concentrated in a very small region at the center known as nucleus.
The positive charge on the nucleus is due to protons. Since the number of protons is different for atoms of different elements, therefore, the magnitude of positive charge on the nucleus is different for atoms of different elements.
Nucleus is surrounded by negatively charged electrons. Number of electrons in an atom is equal to the number of protons (positively charged) in the nucleus. Thus, the atom as a whole is neutral.
The electrons are revolving around the nucleus at very high speed.
Most of the space in an atom is empty.
Rutherford’s Atomic Model had Following Limitations –
This atomic model failed to explain stability of atoms.
According to the model, electrons revolve around the positively charged nucleus. It's not possible for a long run as we know atoms are stable while any particle in a circular orbit would undergo acceleration. During acceleration charged particles would radiate energy. Revolving electron will lose energy and finally fall into the nucleus.
This model of atom also failed to explain the existence of definite lines in the hydrogen spectrum.
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