That's a common misconception! While it's true that protons are much more massive than electrons (about 1836 times heavier), you cannot simply neglect the mass of electrons when determining an atom's mass. Here's why:

* Significant Contribution: Even though individual electrons are much lighter, the number of electrons in an atom is usually equal to the number of protons. This means the total mass of electrons is a substantial fraction of the atom's mass, especially for lighter elements.

* Chemical Reactions: Electrons are the primary players in chemical reactions, and their mass influences the energy levels and stability of atoms and molecules. Neglecting their mass would lead to inaccurate predictions about chemical behavior.

* Atomic Mass Units: The standard atomic mass unit (amu) is defined based on the mass of a carbon-12 atom. This definition accounts for the masses of both protons and neutrons, as well as the electrons.

In Summary:

While the mass of an individual electron is tiny compared to a proton, the collective mass of electrons in an atom is significant enough to impact its overall mass and influence chemical reactions. It's essential to consider the mass of both protons and electrons for accurate calculations and understanding of atomic behavior.