The atomic mass of an atom is primarily the sum of its protons and neutrons, which are both found in the nucleus of the atom. Protons are positively charged particles, while neutrons have no charge. Electrons, which are negatively charged and found outside the nucleus, have a negligible mass compared to protons and neutrons and do not significantly contribute to the overall atomic mass.
To put it simply, when you look at the atomic mass listed on the periodic table for an element, it reflects the total number of protons and neutrons in the atom’s nucleus. For example, a carbon atom has 6 protons and usually 6 neutrons, giving it an atomic mass of roughly 12 atomic mass units (amu). This relationship is crucial in understanding the structure of atoms and how they interact in chemical reactions.