Electrons, which are negatively charged subatomic particles, are the constituents of an atom that have negligible mass. While electrons do have a mass, it is significantly smaller compared to the mass of protons and neutrons.
The mass of an electron is approximately 9.10938356 × 10^-31 kilograms, which is about 1/1836th the mass of a proton or neutron. In comparison to the overall mass of an atom, the mass of electrons is considered negligible for most practical purposes.
Protons and neutrons, on the other hand, are located in the nucleus of an atom and contribute the majority of the atom's mass. Protons have a positive charge, while neutrons have no charge. Together, they form the nucleus of an atom and account for almost the entire mass of the atom.