What subatomic particles mainly contribute to the mass of the entire atom?
The nuclear particles, i.e. the protons and neutrons....
Nuclei are composed of massive particles, as compared to the electrons, the which are conserved to whizz around the nucular core. Protons are massive particles with unit positive electric charge; neutrons are massive particles with NO electric charge. Together these constitute MOST (>99.9%) of the mass of the atom.
At short intranuclear distances protons and neutrons engage in the strong nuclear force, the which, at short ranges, is strong enuff to overcome electrostatic repulsion between like-charged particles, and an attractive force results...
Protons and neutrons.
The protons and neutrons make up the nucleus. They both have a relative atomic mass of 1 compared to the electron which has a mass of 0.0005. This means, despite the nucleus being the smallest part of the atom, as the electron shell makes up most of it, the nucleus actually provides most of the mass.