What is the relationship between the number of protons and the mass number?

The relationship between the number of protons and the mass number is reflected in the fundamental definition of mass number itself. Mass number is defined as the total number of protons and neutrons present in an atom's nucleus. Since protons are positively charged particles that contribute significantly to the mass of an atom, an increase in the number of protons will generally result in an increase in the mass number, assuming the number of neutrons remains constant or increases as well.

Every element has a unique number of protons that defines it, known as the atomic number. When the number of protons increases, the element changes, and the resulting atom will likely have a greater mass number because it inherently contains more matter. This demonstrates that the mass number is not only influenced by protons but also by neutrons, but the overall statement holds true that more protons contribute to a larger mass number. This understanding helps to clarify the relationship between atomic structure and mass, providing foundational knowledge in chemistry.