No, adding or removing an electron from an atom does not change its mass significantly. The mass of an electron is extremely small compared to the mass of protons and neutrons in the atomic nucleus.
The mass of an atom is determined by the combined mass of its protons, neutrons, and electrons. The protons and neutrons, located in the nucleus, contribute the majority of the atom's mass, while the electrons, which orbit around the nucleus in energy levels or shells, have a negligible mass compared to the other two particles.
When an electron is added or removed from an atom, it does not significantly affect the overall mass of the atom. This is because the mass of an electron is approximately 1/1836th the mass of a proton or neutron. Therefore, even if electrons are added or removed, the change in mass is virtually negligible.
However, it's worth noting that there can be extremely rare cases where the removal or addition of an electron can result in a very tiny change in the atom's mass due to the conversion of mass to energy or vice versa, according to Einstein's mass-energy equivalence (E=mc²). Nonetheless, these effects are typically negligible and do not have a noticeable impact on the atom's mass in most practical situations.