The mass of an atom primarily comes from its constituent particles, namely protons, neutrons, and electrons.
Protons and neutrons are located in the nucleus of an atom, which is located at its center. Protons have a positive charge, while neutrons have no charge (they are neutral). Both protons and neutrons are collectively referred to as nucleons. The nucleons contribute significantly to the mass of an atom, as they have a relatively large mass compared to electrons.
Electrons, on the other hand, have a negligible mass compared to protons and neutrons. They are negatively charged particles that orbit around the nucleus in specific energy levels or orbitals. Although electrons contribute little to the overall mass of an atom, they play a crucial role in determining its chemical and electrical properties.
The mass of an atom is primarily determined by the sum of the masses of its protons and neutrons. Electrons contribute very little to the total mass due to their relatively small mass compared to protons and neutrons. The atomic mass unit (amu) is the standard unit used to express the mass of an atom, and it is defined as one-twelfth the mass of a carbon-12 atom.
In summary, the mass of an atom comes from its protons and neutrons in the nucleus, while the electrons contribute minimally to the total mass.