What are #"atomic number"#, and #"mass number"#, and how do these terms relate to nuclear structure?

1 Answer
Feb 4, 2016


All of these terms relate to the number of fundamental particles that are present in the atomic nucleus.


The nucleus contains either protons, fundamental particles with positive charge, or neutrons, fundamental particles with neutral charge. The number of protons, #Z#, is the atomic number, and this number determines elemental identity: #Z=1#, hydrogen; #Z=2#, helium; #Z=3#, lithium; #Z=6#, rubidium; #Z=37#, rubidium. Do you have to remember these numbers? No, because in every test in Chemistry and Physics you should and must be supplied with a Periodic Table of elements.

The atomic mass and mass number relate to the SUM of protons and neutrons contained in the atomic nuclei. Electrons, fundamental negative particles that are conceived to orbit atomic nuclei, do have some mass, but it can be ignored to a 1st (or 2nd) approximation. Atomic mass is determined by the number of massive particles, protons and neutrons, and electrons to a much lesser extent, that are present in the atom.