The atomic mass of an atom is primarily made up of the total mass of its protons and neutrons, which are located in the nucleus. Protons and neutrons each have a mass of approximately 1 atomic mass unit (amu). Electrons also contribute to the atomic mass but their mass is so small compared to protons and neutrons that it is usually negligible. Therefore, the atomic mass is basically the sum of the number of protons and neutrons in the nucleus of the atom. To summarize:
- Protons and neutrons each contribute about 1 amu to the atomic mass.
- Electrons have a much smaller mass and contribute very little to the atomic mass.
- The total atomic mass is approximately the mass number, which is the sum of protons and neutrons.
This explains why the atomic mass is roughly equal to the number of protons plus the number of neutrons in an atom.
