The mass number, also known as the nucleon number, is a concept used in nuclear physics to describe an atomic nucleus. It represents the total number of protons and neutrons in the nucleus of an atom. The mass number is typically denoted by the letter "A."
The mass number provides two important pieces of information about an atomic nucleus:
Number of nucleons: The mass number tells you the total number of nucleons (protons and neutrons) in the nucleus. It is the sum of the number of protons (which determines the element) and the number of neutrons. For example, if an atom has 6 protons (carbon) and 8 neutrons, its mass number would be 14.
Isotopes: Atoms of the same element can have different numbers of neutrons, leading to variations in the mass number. These different forms of an element are called isotopes. Isotopes have the same atomic number (number of protons) but different mass numbers. For instance, carbon-12, carbon-13, and carbon-14 are three isotopes of carbon, with mass numbers 12, 13, and 14, respectively.
In summary, the mass number provides information about the number of nucleons in a nucleus and helps identify different isotopes of an element.