As we all know Atom is smallest particle of an element still having the same chemical properties of the element. There are 2 sextillion atoms of oxygen in one drop of the water. Particles smaller then Atom are called subatomic particles. Electrons, protons and neutrons are the three major subatomic particles. Today scientists understand that protons and neutrons are made of even smaller particles called quarks which are tied together with particles called gluons.
It is believed that an atom is made of 200 or more than 200 subatomic particles because it is told that in an atom there is so much space and electrons take only 1/1000th volume. That space may have more subatomic particles in it and according to the calculations there may come more than 200 subatomic particles. Bellow is the picture of atoms of gold produced by electronic microscope.