Structure of ATOM

As you are aware, the atom is composed of three basic particles:
(a) Electrons
(b) Protons
(c) Neutrons 
Protons and Neutrons form the central portion ofthe atom which is called Nucleus while electrons move in approximately elliptic orbit about the nucleus. The mass of the protons and neutron is approximately same The difference between the two is that the proton is a positively charged particle and neutron is an electrically neutral particle.
          The electrons which revolve around the nucleus are very light in weight. An electrons is 1850 times lighter than a proton orneutron, this is because almost total mass of an is concentrated in its nucleus. Also electrons are negatively charged particles atom. The number of orbiting electrons are always equal to number of protons for any atom thus making atom electrically neutral.