Discovery of nucleus

 

In 1911, Lord Rutherford, a scientist from New Zealand, directed a stream of alpha partials toward a very thin gold foil. He selected a gold foil because he wanted as a thin a layer as possible and gold is the most malleable metal.

He observed that:

 

1.     ➧ Most of the alpha particles passed straight through the foil.

2.      ➧Some alpha particles were slightly deflected from their straight path.

3.    ➧   Very few alpha particles were either deflected by very large angles or   completely bounced back.

   ➧Later, Rutherford generalised these results of alpha particles scattering experiment and suggested a model of the atom that is known as Rutherford Atomic Model.

    An alpha particle is a doubly charged helium ion He²⁺, containing two protons and two   neutrons. It is formed by removing of two electrons from helium atom.

According to this model:

 

1.      The atom contains a large empty space.

2.    There is a positively charged mass at the center of the atoms, known as the nucleus, in which the entire mass of the atoms is concentrated.

3.    The size of the nucleus is very small.

4.     The electrons revolve around the nucleus at large distances from each other and from the nucleus.

5.     An atom as a whole is electrically neutral, because the total positive charge of the nucleus is balanced by the total negatively charge of the electrons.

Rutherford model of atomic structure is similar to structure of the solar system. Just as in the solar system, the sun is as the center having the maximum mass and the planet revolved around it, similarly in an atom the nucleus contains the main mass and the electrons revolve around it and orbit shells.