The particle of an atom that has the least mass is the electron. Electrons are subatomic particles that carry a negative charge and are found in the electron cloud surrounding the nucleus of an atom.
To understand why electrons have the least mass, let’s compare them to the other two main particles found in an atom: protons and neutrons. Protons, which carry a positive charge, and neutrons, which have no charge, are located in the nucleus at the center of the atom. Both protons and neutrons have a mass that is approximately 1836 times greater than that of an electron.
This significant difference in mass means that when considering the overall mass of an atom, the contributions from its electrons are negligible. For example, while the mass of a proton is about 1.007 atomic mass units (amu) and that of a neutron is approximately 1.008 amu, the mass of an electron is roughly 0.0005 amu. Thus, electrons play a crucial role in determining the chemical properties of elements, while having a minimal impact on the atom’s total mass.