Dear Student,
The particles present inside the atom, which are smaller in size than the atom are called sub atomic particles.
The three subatomic particles are electrons, protons and neutrons.
Electrons are negatively charged particle of negligible mass which revolves around the nucleus on an atom in fixed orbits.
Protons are positively charged particles that constitutes the mass of an atom along with the neutrons. Neutrons are neutral particles. Protons and neutrons are present in the centre of an atom i.e. in the nucleus of an atom.
Regards,