Mass number

The mass number of an atom is the total count of protons and neutrons in its nucleus. It is represented by the symbol \(A\). The mass number provides an indication of the mass of the atom, as protons and neutrons contribute significantly to the atomic mass, while electrons have negligible mass in comparison. For example, if an atom has 6 protons and 6 neutrons, its mass number would be \(6 + 6 = 12\).