Explain where most of the mass of an atom is located. also, explain why some particles that make up the atom do not contribute much to its mass.

Within an atom, there are three elementary particles: the proton, neutron, and electron. Most of the mass of an atom is situated within the nucleus, which is the central part of the atom. It is made up of protons and neutrons, which are the heaviest subatomic particles. The electrons within the atom, orbit around the nucleus at a very far distance. Electrons are also a part of the lightest group of subatomic particles called leptons. That is why these electrons don't contribute much to the majority of an atoms mass. They are very light and they orbit at very far distances.

Most mass of the atom is concentrated in the nucleus of the atom. The nucleus is located at the center of the atom which contains the subatomic particles such as neutrons and protons. Neutrons bear no charge while protons are subatomic particles with positive charges. The electron do not make up much of the mass because they just surround the nucleus