Final answer:
Electrons are considered but their mass is often negligible compared to protons and neutrons.
Step-by-step explanation:
When determining the mass of an element, we do consider electrons. However, the mass of an electron is extremely small compared to the mass of protons and neutrons in an atom, so it is often negligible. The mass of an element is primarily determined by the sum of the masses of its protons and neutrons in the nucleus. For example, the mass of a carbon atom is approximately 12 atomic mass units (amu), which is primarily due to the combined mass of its 6 protons and 6 neutrons. Electrons contribute very little to this mass.
Learn more about Mass of elements and the role of electrons