Structure of the atom consists of two parts:
The atomic structure of an element refers to the constitution of its nucleus and the arrangement of the electrons around it. Primarily, the atomic structure of matter is made up of protons, electrons and neutrons. The protons and neutrons make up the nucleus of the atom, which is surrounded by the electrons belonging to the atom. The atomic number of an element describes the total number of protons in its nucleus.
In the year 1897, a British Physicist named J.J Thompson proposed that an atom constitutes of at least one negatively charged particle. He named it corpuscles which was later called electron. e represents an electron and it contributes to the negative charge of an atom.
Proton was discovered by Rutherford when he conducted the famous gold foil experiment. In 1886 Goldstein discovered the presence of positively charged rays while experimenting with the discharged tube using perforated cathode. The rays were named as anode rays or canal rays. A series of experiments led to the discovery of protons. Protons are the particles that contribute to the positive charge of the atom. “p” represents proton.
The discovery of neutron didn't happen until the year 1932. James Chadwick discovered the neutron. He used scattered particle to calculate the mass of the neutral particle. The subatomic particle "neutron" is present in an atom's nucleus."n" represents neutron. It is a neutral particle. Gram is not an appropriate unit for the calculation of such tiny subatomic particles. But Dalton or amu (atomic mass unit) is appropriate.