The three particles of the atom are the proton, neutron and electron. The proton and neutron both reside in the nucleus of the atom and are positively charged and neutral, respectively. The electron is outside the nucleus and has a negative charge.
Neutrons are the most massive of the three sub-atomic particles with a mass of 1.674 x 10^-27 kilograms. Protons have a mass very similar to neutrons, but slightly smaller. A proton has a mass of 1.672 x 10^-27 kilograms. Electrons are by far the smallest of the three sub-atomic particles, with a mass of only 9.109 x 10^-31 kilograms.