<P> The mass number ( symbol A , from the German word Atomgewicht ( atomic weight ) , also called atomic mass number or nucleon number , is the total number of protons and neutrons ( together known as nucleons ) in an atomic nucleus . It determines the atomic mass of atoms . Because protons and neutrons both are baryons , the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion . The mass number is different for each different isotope of a chemical element . This is not the same as the atomic number ( Z ) which denotes the number of protons in a nucleus , and thus uniquely identifies an element . Hence , the difference between the mass number and the atomic number gives the number of neutrons ( N ) in a given nucleus : N = A − Z ( \ displaystyle N = A-Z ) . </P>
<P> The mass number ( symbol A , from the German word Atomgewicht ( atomic weight ) , also called atomic mass number or nucleon number , is the total number of protons and neutrons ( together known as nucleons ) in an atomic nucleus . It determines the atomic mass of atoms . Because protons and neutrons both are baryons , the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion . The mass number is different for each different isotope of a chemical element . This is not the same as the atomic number ( Z ) which denotes the number of protons in a nucleus , and thus uniquely identifies an element . Hence , the difference between the mass number and the atomic number gives the number of neutrons ( N ) in a given nucleus : N = A − Z ( \ displaystyle N = A-Z ) . </P>
what is the sum of the protons and neutrons in an atom
what is the sum of the protons and neutrons in an atom
mass number
mass number