atomimassalukuihin

Atomimassalukuihin are the integers that express the total number of protons and neutrons in the nucleus of an atom. They are denoted by A and are used to describe isotopes, where atoms of the same element have the same atomic number Z (the number of protons) but different mass numbers A because they contain different numbers of neutrons N (N = A − Z).

The mass number A is determined by adding the number of protons and neutrons in the nucleus: A = Z + N. For example, carbon-12 has Z = 6 and N = 6, giving A = 12 (written as 12C). Iron-56 has Z = 26 and N = 30, so A = 56 (written as 56Fe). Isotopes of an element share the same Z but have different A values due to varying neutron counts.

Mass number is distinct from atomic mass or molar mass. A is an integer that counts nucleons, whereas atomic mass is a weighted average of the masses of all natural isotopes of an element, expressed in atomic mass units (amu). The molar mass, measured in grams per mole, is related closely to the atomic mass but reflects natural isotopic abundances. Real nuclear masses differ slightly from the mass number because of binding energy (mass defect).

In practice, A is useful in nuclear chemistry and physics for identifying isotopes, balancing nuclear equations, and understanding nuclear stability and reactions. It helps distinguish isotopes in research, dating methods, and astrophysical contexts where neutron-rich or neutron-poor nuclei play a role.