yep they do .. electrons have mass .. so do protons and neutrons ... and when atoms make up material the way they are arranged affects the density of that material ..
The majority of the volume in an atom is filled by the neutrons and the protons. Although the electrons do have a volume, they occupy significantly less space than the other two subatomic particles
It can be determined by the size of it's electron. The reason for this being is because of the mass that is calculated by the protons to the neutrons of the atoms within the nucleus.