The Road to Atomic Physics:-

As we know from previous article atomic physics is nothing but,
the scientific study of the structure of the atom, its energy states, and its
interactions with other particles and with electric and magnetic fields.

Now let’s take a look on journey behind today’s atomic physics-its discoveries the things we cannot see. The notion that matter is made of fundamental building blocks dates to the ancient rishis, who speculated that earth, air, fire, and water might form the basic elements from which the physical world is constructed. 

For the first time some disturbance was noted by British physicist J. J. Thomson that proved atoms were not the most basic form of matter. He demonstrated that cathode rays could be deflected, or bent, by magnetic or electric fields, which indicated that cathode rays consist of charged particles. These particles which show deflection were negatively charged cathode because these rays were repelled by the negative terminal of an electric field. As according to law of attraction same charges repel each other and opposite charges attract. Thomson concluded that the particles had a net negative charge; these particles are now called electrons.

Similarly, anode rays or better called as canal rays were discovered with some slight changes in the experimental set up used for cathode rays performed by Thomson. So, the credit of discovery of canal rays goes to a German scientist, Eugen Goldstein. These positively charged particles were named as protons by a British scientist, Ernest Rutherford.

The second line of investigation began in 1896, when the
French physicist Henri Becquerel discovered that certain minerals, such as
uranium salts, emitted a new form of energy. Becquerel’s work was greatly
extended by Marie Curie and her husband, Pierre. Marie Curie coined the term
radioactivity (from the Latin radius, meaning “ray”) to describe the emission
of energy rays by matter. 

Building on the Curies’ work Ernest Rutherford performed
decisive experiments that led to the modern view of the structure of the atom. Rutherford's
α-ray scattering experiment was the basic of atomic model. Rutherford passed
beams of alpha particles through a  thin
gold foil to observe the atom and noted how the alpha particles scattered from
the foil. 

Observations of Rutherford's alpha ray scattering
experiment:

1. Most of the α-particles passed straight through the gold
foil without any deviation.

2. Some of the α-particles were deflected by the foil by
some angles.

 3. Interestingly one
out of every 12,000 alpha particles appeared to rebound







Conclusion of Rutherford's scattering experiment:

1. Most of the space inside the atom is empty because most
of the α-particles passed through the gold foil without getting deflected.

2. Very few particles were deflected from their path,
indicating that the positive charge of the atom occupies very little space.





 3. A very small
fraction of α-particles were deflected by very large angles, indicating that
all the positive charge and mass of the gold atom were concentrated in a very
small volume within the atom.